Added revision sum as tracking for filesystem stability

The idea is pretty simple: The revision count for each metadata block only really needs 3 distinct states. The additional bit-width of the revision count is available for other information. In this case, we can sum all revision counts in the filesystem to encode state that can be updated for free during any metadata block update. The obvious state to store first is if the filesystem is in a bad state that requires a deorphan step. The allows us to sidestep the expensive O(n^2) operation for the O(n) sum in the much more common case. This patch adds the following rule: If the sum of all revision count is odd, the filesystem was caught mid-operation and must be deorphaned.
2025-11-01 16:14:13 +01:00 · 2017-10-10 18:27:56 -05:00
22 changed files with 887 additions and 2487 deletions
--- a/.gitignore
+++ b/.gitignore
@@ -1,9 +0,0 @@
 # Compilation output
 *.o
 *.d
 *.a
 # Testing things
 blocks/
 lfs
 test.c
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,223 +1,48 @@
 # Environment variables
 env:
  global:
    - CFLAGS=-Werror
 # Common test script
 script:
-  # make sure example can at least compile
+    # make sure example can at least compile
-  - sed -n '/``` c/,/```/{/```/d; p;}' README.md > test.c &&
+    - sed -n '/``` c/,/```/{/```/d; p;}' README.md > test.c &&
-    make all CFLAGS+="
+      CFLAGS='
        -Duser_provided_block_device_read=NULL
        -Duser_provided_block_device_prog=NULL
        -Duser_provided_block_device_erase=NULL
        -Duser_provided_block_device_sync=NULL
-        -include stdio.h"
+        -include stdio.h -Werror' make all size
-  # run tests
+    # run tests
-  - make test QUIET=1
+    - make test
-  # run tests with a few different configurations
+    # run tests with a few different configurations
-  - make test QUIET=1 CFLAGS+="-DLFS_READ_SIZE=1      -DLFS_PROG_SIZE=1"
+    - CFLAGS="-DLFS_READ_SIZE=1   -DLFS_PROG_SIZE=1"   make test
-  - make test QUIET=1 CFLAGS+="-DLFS_READ_SIZE=512    -DLFS_PROG_SIZE=512"
+    - CFLAGS="-DLFS_READ_SIZE=512 -DLFS_PROG_SIZE=512" make test
-  - make test QUIET=1 CFLAGS+="-DLFS_BLOCK_COUNT=1023 -DLFS_LOOKAHEAD=2048"
+    - CFLAGS="-DLFS_BLOCK_COUNT=1023" make test
-
+    - CFLAGS="-DLFS_LOOKAHEAD=2047"   make test
  - make clean test QUIET=1 CFLAGS+="-DLFS_NO_INTRINSICS"
  # compile and find the code size with the smallest configuration
  - make clean size
        OBJ="$(ls lfs*.o | tr '\n' ' ')"
        CFLAGS+="-DLFS_NO{ASSERT,DEBUG,WARN,ERROR}"
        | tee sizes
  # update status if we succeeded, compare with master if possible
  - |
    if [ "$TRAVIS_TEST_RESULT" -eq 0 ]
    then
        CURR=$(tail -n1 sizes | awk '{print $1}')
        PREV=$(curl https://api.github.com/repos/$TRAVIS_REPO_SLUG/status/master \
            | jq -re "select(.sha != \"$TRAVIS_COMMIT\")
                | .statuses[] | select(.context == \"$STAGE/$NAME\").description
                | capture(\"code size is (?<size>[0-9]+)\").size" \
            || echo 0)
        STATUS="Passed, code size is ${CURR}B"
        if [ "$PREV" -ne 0 ]
        then
            STATUS="$STATUS ($(python -c "print '%+.2f' % (100*($CURR-$PREV)/$PREV.0)")%)"
        fi
    fi
 # CI matrix
 jobs:
  include:
    # native testing
    - stage: test
      env:
        - STAGE=test
        - NAME=littlefs-x86
    # cross-compile with ARM (thumb mode)
    - stage: test
      env:
        - STAGE=test
        - NAME=littlefs-arm
        - CC="arm-linux-gnueabi-gcc --static -mthumb"
        - EXEC="qemu-arm"
      install:
        - sudo apt-get install gcc-arm-linux-gnueabi qemu-user
        - arm-linux-gnueabi-gcc --version
        - qemu-arm -version
    # cross-compile with PowerPC
    - stage: test
      env:
        - STAGE=test
        - NAME=littlefs-powerpc
        - CC="powerpc-linux-gnu-gcc --static"
        - EXEC="qemu-ppc"
      install:
        - sudo apt-get install gcc-powerpc-linux-gnu qemu-user
        - powerpc-linux-gnu-gcc --version
        - qemu-ppc -version
    # cross-compile with MIPS
    - stage: test
      env:
        - STAGE=test
        - NAME=littlefs-mips
        - CC="mips-linux-gnu-gcc --static"
        - EXEC="qemu-mips"
      install:
        - sudo add-apt-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial main universe"
        - sudo apt-get -qq update
        - sudo apt-get install gcc-mips-linux-gnu qemu-user
        - mips-linux-gnu-gcc --version
        - qemu-mips -version
    # self-host with littlefs-fuse for fuzz test
-    - stage: test
+    - make -C littlefs-fuse
      env:
        - STAGE=test
        - NAME=littlefs-fuse
      install:
        - sudo apt-get install libfuse-dev
        - git clone --depth 1 https://github.com/geky/littlefs-fuse
        - fusermount -V
        - gcc --version
      before_script:
        # setup disk for littlefs-fuse
        - rm -rf littlefs-fuse/littlefs/*
        - cp -r $(git ls-tree --name-only HEAD) littlefs-fuse/littlefs
-        - mkdir mount
+    - littlefs-fuse/lfs --format /dev/loop0
-        - sudo chmod a+rw /dev/loop0
+    - littlefs-fuse/lfs /dev/loop0 mount
        - dd if=/dev/zero bs=512 count=2048 of=disk
        - losetup /dev/loop0 disk
      script:
        # self-host test
        - make -C littlefs-fuse
-        - littlefs-fuse/lfs --format /dev/loop0
+    - ls mount
-        - littlefs-fuse/lfs /dev/loop0 mount
+    - mkdir mount/littlefs
    - cp -r $(git ls-tree --name-only HEAD) mount/littlefs
    - cd mount/littlefs
    - ls
    - make -B test_dirs
        - ls mount
        - mkdir mount/littlefs
        - cp -r $(git ls-tree --name-only HEAD) mount/littlefs
        - cd mount/littlefs
        - ls
        - make -B test_dirs test_files QUIET=1
      # Automatically update releases
    - stage: deploy
      env:
        - STAGE=deploy
        - NAME=deploy
      script:
        # Update tag for version defined in lfs.h
        - LFS_VERSION=$(grep -ox '#define LFS_VERSION .*' lfs.h | cut -d ' ' -f3)
        - LFS_VERSION_MAJOR=$((0xffff & ($LFS_VERSION >> 16)))
        - LFS_VERSION_MINOR=$((0xffff & ($LFS_VERSION >>  0)))
        - LFS_VERSION="v$LFS_VERSION_MAJOR.$LFS_VERSION_MINOR"
        - echo "littlefs version $LFS_VERSION"
        - |
          curl -u $GEKY_BOT_RELEASES -X POST \
            https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs \
            -d "{
              \"ref\": \"refs/tags/$LFS_VERSION\",
              \"sha\": \"$TRAVIS_COMMIT\"
            }"
        - |
          curl -f -u $GEKY_BOT_RELEASES -X PATCH \
            https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs/tags/$LFS_VERSION \
            -d "{
              \"sha\": \"$TRAVIS_COMMIT\"
            }"
        # Create release notes from commits
        - LFS_PREV_VERSION="v$LFS_VERSION_MAJOR.$(($LFS_VERSION_MINOR-1))"
        - |
          if [ $(git tag -l "$LFS_PREV_VERSION") ]
          then
            curl -u $GEKY_BOT_RELEASES -X POST \
                https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases \
                -d "{
                    \"tag_name\": \"$LFS_VERSION\",
                    \"name\": \"$LFS_VERSION\"
                }"
            RELEASE=$(
                curl -f https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases/tags/$LFS_VERSION
            )
            CHANGES=$(
                git log --oneline $LFS_PREV_VERSION.. --grep='^Merge' --invert-grep
            )
            curl -f -u $GEKY_BOT_RELEASES -X PATCH \
                https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases/$(
                    jq -r '.id' <<< "$RELEASE"
                ) \
                -d "$(
                    jq -s '{
                        "body": ((.[0] // "" | sub("(?<=\n)#+ Changes.*"; ""; "mi"))
                            + "### Changes\n\n" + .[1])
                    }' <(jq '.body' <<< "$RELEASE") <(jq -sR '.' <<< "$CHANGES")
                )"
          fi
 # Manage statuses
 before_install:
-  - |
+    - fusermount -V
-    curl -u $GEKY_BOT_STATUSES -X POST \
+    - gcc --version
        https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
        -d "{
            \"context\": \"$STAGE/$NAME\",
            \"state\": \"pending\",
            \"description\": \"${STATUS:-In progress}\",
            \"target_url\": \"https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$TRAVIS_JOB_ID\"
        }"
-after_failure:
+install:
-  - |
+    - sudo apt-get install libfuse-dev
-    curl -u $GEKY_BOT_STATUSES -X POST \
+    - git clone --depth 1 https://github.com/geky/littlefs-fuse
        https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
        -d "{
            \"context\": \"$STAGE/$NAME\",
            \"state\": \"failure\",
            \"description\": \"${STATUS:-Failed}\",
            \"target_url\": \"https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$TRAVIS_JOB_ID\"
        }"
-after_success:
+before_script:
-  - |
+    - rm -rf littlefs-fuse/littlefs/*
-    curl -u $GEKY_BOT_STATUSES -X POST \
+    - cp -r $(git ls-tree --name-only HEAD) littlefs-fuse/littlefs
        https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
        -d "{
            \"context\": \"$STAGE/$NAME\",
            \"state\": \"success\",
            \"description\": \"${STATUS:-Passed}\",
            \"target_url\": \"https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$TRAVIS_JOB_ID\"
        }"
-# Job control
+    - mkdir mount
-stages:
+    - sudo chmod a+rw /dev/loop0
-    - name: test
+    - dd if=/dev/zero bs=512 count=2048 of=disk
-    - name: deploy
+    - losetup /dev/loop0 disk
      if: branch = master AND type = push
--- a/DESIGN.md
+++ b/DESIGN.md
@@ -1,6 +1,6 @@
 ## The design of the little filesystem
-A little fail-safe filesystem designed for embedded systems.
+The littlefs is a little fail-safe filesystem designed for embedded systems.
 ```
   | | |     .---._____
@@ -16,9 +16,9 @@ more about filesystem design by tackling the relative unsolved problem of
 managing a robust filesystem resilient to power loss on devices
 with limited RAM and ROM.
-The embedded systems the littlefs is targeting are usually 32 bit
+The embedded systems the littlefs is targeting are usually 32bit
-microcontrollers with around 32KB of RAM and 512KB of ROM. These are
+microcontrollers with around 32Kbytes of RAM and 512Kbytes of ROM. These are
-often paired with SPI NOR flash chips with about 4MB of flash storage.
+often paired with SPI NOR flash chips with about 4Mbytes of flash storage.
 Flash itself is a very interesting piece of technology with quite a bit of
 nuance. Unlike most other forms of storage, writing to flash requires two
@@ -27,23 +27,22 @@ cheap, and can be very granular. For NOR flash specifically, byte-level
 programs are quite common. Erasing, however, requires an expensive operation
 that forces the state of large blocks of memory to reset in a destructive
 reaction that gives flash its name. The [Wikipedia entry](https://en.wikipedia.org/wiki/Flash_memory)
-has more information if you are interested in how this works.
+has more information if you are interesting in how this works.
 This leaves us with an interesting set of limitations that can be simplified
 to three strong requirements:
-1. **Power-loss resilient** - This is the main goal of the littlefs and the
+1. **Fail-safe** - This is actually the main goal of the littlefs and the focus
-   focus of this project.
+   of this project. Embedded systems are usually designed without a shutdown
-
+   routine and a notable lack of user interface for recovery, so filesystems
-   Embedded systems are usually designed without a shutdown routine and a
+   targeting embedded systems should be prepared to lose power an any given
-   notable lack of user interface for recovery, so filesystems targeting
+   time.
   embedded systems must be prepared to lose power at any given time.
   Despite this state of things, there are very few embedded filesystems that
-   handle power loss in a reasonable manner, and most can become corrupted if
+   handle power loss in a reasonable manner, and can become corrupted if the
-   the user is unlucky enough.
+   user is unlucky enough.
-2. **Wear leveling** - Due to the destructive nature of flash, most flash
+2. **Wear awareness** - Due to the destructive nature of flash, most flash
   chips have a limited number of erase cycles, usually in the order of around
   100,000 erases per block for NOR flash. Filesystems that don't take wear
   into account can easily burn through blocks used to store frequently updated
@@ -53,8 +52,7 @@ to three strong requirements:
   which stores a file allocation table (FAT) at a specific offset from the
   beginning of disk. Every block allocation will update this table, and after
   100,000 updates, the block will likely go bad, rendering the filesystem
-   unusable even if there are many more erase cycles available on the storage
+   unusable even if there are many more erase cycles available on the storage.
   as a whole.
 3. **Bounded RAM/ROM** - Even with the design difficulties presented by the
   previous two limitations, we have already seen several flash filesystems
@@ -74,32 +72,33 @@ to three strong requirements:
 ## Existing designs?
-There are of course, many different existing filesystem. Here is a very rough
+There are of course, many different existing filesystem. Heres a very rough
 summary of the general ideas behind some of them.
 Most of the existing filesystems fall into the one big category of filesystem
 designed in the early days of spinny magnet disks. While there is a vast amount
 of interesting technology and ideas in this area, the nature of spinny magnet
-disks encourage properties, such as grouping writes near each other, that don't
+disks encourage properties such as grouping writes near each other, that don't
 make as much sense on recent storage types. For instance, on flash, write
-locality is not important and can actually increase wear.
+locality is not as important and can actually increase wear destructively.
 One of the most popular designs for flash filesystems is called the
 [logging filesystem](https://en.wikipedia.org/wiki/Log-structured_file_system).
 The flash filesystems [jffs](https://en.wikipedia.org/wiki/JFFS)
-and [yaffs](https://en.wikipedia.org/wiki/YAFFS) are good examples. In a
+and [yaffs](https://en.wikipedia.org/wiki/YAFFS) are good examples. In
-logging filesystem, data is not stored in a data structure on disk, but instead
+logging filesystem, data is not store in a data structure on disk, but instead
 the changes to the files are stored on disk. This has several neat advantages,
-such as the fact that the data is written in a cyclic log format and naturally
+such as the fact that the data is written in a cyclic log format naturally
 wear levels as a side effect. And, with a bit of error detection, the entire
 filesystem can easily be designed to be resilient to power loss. The
-journaling component of most modern day filesystems is actually a reduced
+journalling component of most modern day filesystems is actually a reduced
 form of a logging filesystem. However, logging filesystems have a difficulty
 scaling as the size of storage increases. And most filesystems compensate by
-caching large parts of the filesystem in RAM, a strategy that is inappropriate
+caching large parts of the filesystem in RAM, a strategy that is unavailable
 for embedded systems.
-Another interesting filesystem design technique is that of [copy-on-write (COW)](https://en.wikipedia.org/wiki/Copy-on-write).
+Another interesting filesystem design technique that the littlefs borrows the
 most from, is the [copy-on-write (COW)](https://en.wikipedia.org/wiki/Copy-on-write).
 A good example of this is the [btrfs](https://en.wikipedia.org/wiki/Btrfs)
 filesystem. COW filesystems can easily recover from corrupted blocks and have
 natural protection against power loss. However, if they are not designed with
@@ -109,14 +108,14 @@ where the COW data structures are synchronized.
 ## Metadata pairs
 The core piece of technology that provides the backbone for the littlefs is
-the concept of metadata pairs. The key idea here is that any metadata that
+the concept of metadata pairs. The key idea here, is that any metadata that
 needs to be updated atomically is stored on a pair of blocks tagged with
 a revision count and checksum. Every update alternates between these two
 pairs, so that at any time there is always a backup containing the previous
 state of the metadata.
 Consider a small example where each metadata pair has a revision count,
-a number as data, and the XOR of the block as a quick checksum. If
+a number as data, and the xor of the block as a quick checksum. If
 we update the data to a value of 9, and then to a value of 5, here is
 what the pair of blocks may look like after each update:
 ```
@@ -132,7 +131,7 @@ what the pair of blocks may look like after each update:
 After each update, we can find the most up to date value of data by looking
 at the revision count.
-Now consider what the blocks may look like if we suddenly lose power while
+Now consider what the blocks may look like if we suddenly loss power while
 changing the value of data to 5:
 ```
  block 1   block 2        block 1   block 2        block 1   block 2
@@ -151,19 +150,19 @@ check our checksum we notice that block 1 was corrupted. So we fall back to
 block 2 and use the value 9.
 Using this concept, the littlefs is able to update metadata blocks atomically.
-There are a few other tweaks, such as using a 32 bit CRC and using sequence
+There are a few other tweaks, such as using a 32bit crc and using sequence
 arithmetic to handle revision count overflow, but the basic concept
 is the same. These metadata pairs define the backbone of the littlefs, and the
 rest of the filesystem is built on top of these atomic updates.
-## Non-meta data
+## Files
 Now, the metadata pairs do come with some drawbacks. Most notably, each pair
 requires two blocks for each block of data. I'm sure users would be very
 unhappy if their storage was suddenly cut in half! Instead of storing
 everything in these metadata blocks, the littlefs uses a COW data structure
 for files which is in turn pointed to by a metadata block. When
-we update a file, we create copies of any blocks that are modified until
+we update a file, we create a copies of any blocks that are modified until
 the metadata blocks are updated with the new copy. Once the metadata block
 points to the new copy, we deallocate the old blocks that are no longer in use.
@@ -186,7 +185,7 @@ Here is what updating a one-block file may look like:
            update data in file        update metadata pair
 ```
-It doesn't matter if we lose power while writing new data to block 5,
+It doesn't matter if we lose power while writing block 5 with the new data,
 since the old data remains unmodified in block 4. This example also
 highlights how the atomic updates of the metadata blocks provide a
 synchronization barrier for the rest of the littlefs.
@@ -201,14 +200,14 @@ Now we could just leave files here, copying the entire file on write
 provides the synchronization without the duplicated memory requirements
 of the metadata blocks. However, we can do a bit better.
-## CTZ skip-lists
+## CTZ linked-lists
 There are many different data structures for representing the actual
 files in filesystems. Of these, the littlefs uses a rather unique [COW](https://upload.wikimedia.org/wikipedia/commons/0/0c/Cow_female_black_white.jpg)
 data structure that allows the filesystem to reuse unmodified parts of the
 file without additional metadata pairs.
-First lets consider storing files in a simple linked-list. What happens when we
+First lets consider storing files in a simple linked-list. What happens when
 append a block? We have to change the last block in the linked-list to point
 to this new block, which means we have to copy out the last block, and change
 the second-to-last block, and then the third-to-last, and so on until we've
@@ -225,12 +224,12 @@ Exhibit A: A linked-list
 To get around this, the littlefs, at its heart, stores files backwards. Each
 block points to its predecessor, with the first block containing no pointers.
-If you think about for a while, it starts to make a bit of sense. Appending
+If you think about this, it makes a bit of sense. Appending blocks just point
-blocks just point to their predecessor and no other blocks need to be updated.
+to their predecessor and no other blocks need to be updated. If we update
-If we update a block in the middle, we will need to copy out the blocks that
+a block in the middle, we will need to copy out the blocks that follow,
-follow, but can reuse the blocks before the modified block. Since most file
+but can reuse the blocks before the modified block. Since most file operations
-operations either reset the file each write or append to files, this design
+either reset the file each write or append to files, this design avoids
-avoids copying the file in the most common cases.
+copying the file in the most common cases.
 ```
 Exhibit B: A backwards linked-list
@@ -242,24 +241,24 @@ Exhibit B: A backwards linked-list
 ```
 However, a backwards linked-list does come with a rather glaring problem.
-Iterating over a file _in order_ has a runtime cost of O(n^2). Gah! A quadratic
+Iterating over a file _in order_ has a runtime of O(n^2). Gah! A quadratic
-runtime to just _read_ a file? That's awful. Keep in mind reading files is
+runtime to just _read_ a file? That's awful. Keep in mind reading files are
 usually the most common filesystem operation.
 To avoid this problem, the littlefs uses a multilayered linked-list. For
-every nth block where n is divisible by 2^x, the block contains a pointer
+every block that is divisible by a power of two, the block contains an
-to block n-2^x. So each block contains anywhere from 1 to log2(n) pointers
+additional pointer that points back by that power of two. Another way of
-that skip to various sections of the preceding list. If you're familiar with
+thinking about this design is that there are actually many linked-lists
-data-structures, you may have recognized that this is a type of deterministic
+threaded together, with each linked-lists skipping an increasing number
-skip-list.
+of blocks. If you're familiar with data-structures, you may have also
 recognized that this is a deterministic skip-list.
-The name comes from the use of the
+To find the power of two factors efficiently, we can use the instruction
-[count trailing zeros (CTZ)](https://en.wikipedia.org/wiki/Count_trailing_zeros)
+[count trailing zeros (CTZ)](https://en.wikipedia.org/wiki/Count_trailing_zeros),
-instruction, which allows us to calculate the power-of-two factors efficiently.
+which is where this linked-list's name comes from.
 For a given block n, the block contains ctz(n)+1 pointers.
 ```
-Exhibit C: A backwards CTZ skip-list
+Exhibit C: A backwards CTZ linked-list
 .--------.  .--------.  .--------.  .--------.  .--------.  .--------.
 | data 0 |<-| data 1 |<-| data 2 |<-| data 3 |<-| data 4 |<-| data 5 |
 |        |<-|        |--|        |<-|        |--|        |  |        |
@@ -267,9 +266,6 @@ Exhibit C: A backwards CTZ skip-list
 '--------'  '--------'  '--------'  '--------'  '--------'  '--------'
 ```
 The additional pointers allow us to navigate the data-structure on disk
 much more efficiently than in a singly linked-list.
 Taking exhibit C for example, here is the path from data block 5 to data
 block 1. You can see how data block 3 was completely skipped:
 ```
@@ -289,132 +285,15 @@ The path to data block 0 is even more quick, requiring only two jumps:
 '--------'  '--------'  '--------'  '--------'  '--------'  '--------'
 ```
-We can find the runtime complexity by looking at the path to any block from
+The CTZ linked-list has quite a few interesting properties. All of the pointers
-the block containing the most pointers. Every step along the path divides
+in the block can be found by just knowing the index in the list of the current
-the search space for the block in half. This gives us a runtime of O(log n).
+block, and, with a bit of math, the amortized overhead for the linked-list is
-To get to the block with the most pointers, we can perform the same steps
+only two pointers per block.  Most importantly, the CTZ linked-list has a
-backwards, which puts the runtime at O(2 log n) = O(log n). The interesting
+worst case lookup runtime of O(logn), which brings the runtime of reading a
-part about this data structure is that this optimal path occurs naturally
+file down to O(n logn). Given that the constant runtime is divided by the
-if we greedily choose the pointer that covers the most distance without passing
+amount of data we can store in a block, this is pretty reasonable.
 our target block.
-So now we have a representation of files that can be appended trivially with
+Here is what it might look like to update a file stored with a CTZ linked-list:
 a runtime of O(1), and can be read with a worst case runtime of O(n log n).
 Given that the the runtime is also divided by the amount of data we can store
 in a block, this is pretty reasonable.
 Unfortunately, the CTZ skip-list comes with a few questions that aren't
 straightforward to answer. What is the overhead? How do we handle more
 pointers than we can store in a block? How do we store the skip-list in
 a directory entry?
 One way to find the overhead per block is to look at the data structure as
 multiple layers of linked-lists. Each linked-list skips twice as many blocks
 as the previous linked-list. Another way of looking at it is that each 
 linked-list uses half as much storage per block as the previous linked-list.
 As we approach infinity, the number of pointers per block forms a geometric
 series. Solving this geometric series gives us an average of only 2 pointers
 per block.
 ![overhead_per_block](https://latex.codecogs.com/svg.latex?%5Clim_%7Bn%5Cto%5Cinfty%7D%5Cfrac%7B1%7D%7Bn%7D%5Csum_%7Bi%3D0%7D%5E%7Bn%7D%5Cleft%28%5Ctext%7Bctz%7D%28i%29&plus;1%5Cright%29%20%3D%20%5Csum_%7Bi%3D0%7D%5Cfrac%7B1%7D%7B2%5Ei%7D%20%3D%202)
 Finding the maximum number of pointers in a block is a bit more complicated,
 but since our file size is limited by the integer width we use to store the
 size, we can solve for it. Setting the overhead of the maximum pointers equal
 to the block size we get the following equation. Note that a smaller block size
 results in more pointers, and a larger word width results in larger pointers.
 ![maximum overhead](https://latex.codecogs.com/svg.latex?B%20%3D%20%5Cfrac%7Bw%7D%7B8%7D%5Cleft%5Clceil%5Clog_2%5Cleft%28%5Cfrac%7B2%5Ew%7D%7BB-2%5Cfrac%7Bw%7D%7B8%7D%7D%5Cright%29%5Cright%5Crceil)
 where:  
 B = block size in bytes  
 w = word width in bits  
 Solving the equation for B gives us the minimum block size for various word
 widths:  
 32 bit CTZ skip-list = minimum block size of 104 bytes  
 64 bit CTZ skip-list = minimum block size of 448 bytes  
 Since littlefs uses a 32 bit word size, we are limited to a minimum block
 size of 104 bytes. This is a perfectly reasonable minimum block size, with most
 block sizes starting around 512 bytes. So we can avoid additional logic to
 avoid overflowing our block's capacity in the CTZ skip-list.
 So, how do we store the skip-list in a directory entry? A naive approach would
 be to store a pointer to the head of the skip-list, the length of the file
 in bytes, the index of the head block in the skip-list, and the offset in the
 head block in bytes. However this is a lot of information, and we can observe
 that a file size maps to only one block index + offset pair. So it should be
 sufficient to store only the pointer and file size.
 But there is one problem, calculating the block index + offset pair from a
 file size doesn't have an obvious implementation.
 We can start by just writing down an equation. The first idea that comes to
 mind is to just use a for loop to sum together blocks until we reach our
 file size. We can write this equation as a summation:
 ![summation1](https://latex.codecogs.com/svg.latex?N%20%3D%20%5Csum_i%5En%5Cleft%5BB-%5Cfrac%7Bw%7D%7B8%7D%5Cleft%28%5Ctext%7Bctz%7D%28i%29&plus;1%5Cright%29%5Cright%5D)
 where:  
 B = block size in bytes  
 w = word width in bits  
 n = block index in skip-list  
 N = file size in bytes  
 And this works quite well, but is not trivial to calculate. This equation
 requires O(n) to compute, which brings the entire runtime of reading a file
 to O(n^2 log n). Fortunately, the additional O(n) does not need to touch disk,
 so it is not completely unreasonable. But if we could solve this equation into
 a form that is easily computable, we can avoid a big slowdown.
 Unfortunately, the summation of the CTZ instruction presents a big challenge.
 How would you even begin to reason about integrating a bitwise instruction?
 Fortunately, there is a powerful tool I've found useful in these situations:
 The [On-Line Encyclopedia of Integer Sequences (OEIS)](https://oeis.org/).
 If we work out the first couple of values in our summation, we find that CTZ
 maps to [A001511](https://oeis.org/A001511), and its partial summation maps
 to [A005187](https://oeis.org/A005187), and surprisingly, both of these
 sequences have relatively trivial equations! This leads us to a rather
 unintuitive property:
 ![mindblown](https://latex.codecogs.com/svg.latex?%5Csum_i%5En%5Cleft%28%5Ctext%7Bctz%7D%28i%29&plus;1%5Cright%29%20%3D%202n-%5Ctext%7Bpopcount%7D%28n%29)
 where:  
 ctz(x) = the number of trailing bits that are 0 in x  
 popcount(x) = the number of bits that are 1 in x  
 It's a bit bewildering that these two seemingly unrelated bitwise instructions
 are related by this property. But if we start to dissect this equation we can
 see that it does hold. As n approaches infinity, we do end up with an average
 overhead of 2 pointers as we find earlier. And popcount seems to handle the
 error from this average as it accumulates in the CTZ skip-list.
 Now we can substitute into the original equation to get a trivial equation
 for a file size:
 ![summation2](https://latex.codecogs.com/svg.latex?N%20%3D%20Bn%20-%20%5Cfrac%7Bw%7D%7B8%7D%5Cleft%282n-%5Ctext%7Bpopcount%7D%28n%29%5Cright%29)
 Unfortunately, we're not quite done. The popcount function is non-injective,
 so we can only find the file size from the block index, not the other way
 around. However, we can solve for an n' block index that is greater than n
 with an error bounded by the range of the popcount function. We can then
 repeatedly substitute this n' into the original equation until the error
 is smaller than the integer division. As it turns out, we only need to
 perform this substitution once. Now we directly calculate our block index:
 ![formulaforn](https://latex.codecogs.com/svg.latex?n%20%3D%20%5Cleft%5Clfloor%5Cfrac%7BN-%5Cfrac%7Bw%7D%7B8%7D%5Cleft%28%5Ctext%7Bpopcount%7D%5Cleft%28%5Cfrac%7BN%7D%7BB-2%5Cfrac%7Bw%7D%7B8%7D%7D-1%5Cright%29&plus;2%5Cright%29%7D%7BB-2%5Cfrac%7Bw%7D%7B8%7D%7D%5Cright%5Crfloor)
 Now that we have our block index n, we can just plug it back into the above
 equation to find the offset. However, we do need to rearrange the equation
 a bit to avoid integer overflow:
 ![formulaforoff](https://latex.codecogs.com/svg.latex?%5Cmathit%7Boff%7D%20%3D%20N%20-%20%5Cleft%28B-2%5Cfrac%7Bw%7D%7B8%7D%5Cright%29n%20-%20%5Cfrac%7Bw%7D%7B8%7D%5Ctext%7Bpopcount%7D%28n%29)
 The solution involves quite a bit of math, but computers are very good at math.
 Now we can solve for both the block index and offset from the file size in O(1).
 Here is what it might look like to update a file stored with a CTZ skip-list:
 ```
                                      block 1   block 2
                                    .---------.---------.
@@ -488,7 +367,7 @@ v
 ## Block allocation
 So those two ideas provide the grounds for the filesystem. The metadata pairs
-give us directories, and the CTZ skip-lists give us files. But this leaves
+give us directories, and the CTZ linked-lists give us files. But this leaves
 one big [elephant](https://upload.wikimedia.org/wikipedia/commons/3/37/African_Bush_Elephant.jpg)
 of a question. How do we get those blocks in the first place?
@@ -501,17 +380,16 @@ scanned to find the most recent free list, but once the list was found the
 state of all free blocks becomes known.
 However, this approach had several issues:
 - There was a lot of nuanced logic for adding blocks to the free list without
  modifying the blocks, since the blocks remain active until the metadata is
  updated.
- The free list had to support both additions and removals in FIFO order while
+- The free list had to support both additions and removals in fifo order while
  minimizing block erases.
 - The free list had to handle the case where the file system completely ran
  out of blocks and may no longer be able to add blocks to the free list.
 - If we used a revision count to track the most recently updated free list,
  metadata blocks that were left unmodified were ticking time bombs that would
-  cause the system to go haywire if the revision count overflowed.
+  cause the system to go haywire if the revision count overflowed
 - Every single metadata block wasted space to store these free list references.
 Actually, to simplify, this approach had one massive glaring issue: complexity.
@@ -541,7 +419,7 @@ would have an abhorrent runtime.
 So the littlefs compromises. It doesn't store a bitmap the size of the storage,
 but it does store a little bit-vector that contains a fixed set lookahead
 for block allocations. During a block allocation, the lookahead vector is
-checked for any free blocks. If there are none, the lookahead region jumps
+checked for any free blocks, if there are none, the lookahead region jumps
 forward and the entire filesystem is scanned for free blocks.
 Here's what it might look like to allocate 4 blocks on a decently busy
@@ -624,7 +502,7 @@ So, as a solution, the littlefs adopted a sort of threaded tree. Each
 directory not only contains pointers to all of its children, but also a
 pointer to the next directory. These pointers create a linked-list that
 is threaded through all of the directories in the filesystem. Since we
-only use this linked list to check for existence, the order doesn't actually
+only use this linked list to check for existance, the order doesn't actually
 matter. As an added plus, we can repurpose the pointer for the individual
 directory linked-lists and avoid using any additional space.
@@ -775,17 +653,9 @@ deorphan step that simply iterates through every directory in the linked-list
 and checks it against every directory entry in the filesystem to see if it
 has a parent. The deorphan step occurs on the first block allocation after
 boot, so orphans should never cause the littlefs to run out of storage
-prematurely. Note that the deorphan step never needs to run in a read-only
+prematurely.
 filesystem.
-## The move problem
+And for my final trick, moving a directory:
 Now we have a real problem. How do we move things between directories while
 remaining power resilient? Even looking at the problem from a high level,
 it seems impossible. We can update directory blocks atomically, but atomically
 updating two independent directory blocks is not an atomic operation.
 Here's the steps the filesystem may go through to move a directory:
 ```
         .--------.
         |root dir|-.
@@ -846,142 +716,25 @@ v
     '--------'
 ```
-We can leave any orphans up to the deorphan step to collect, but that doesn't
+Note that once again we don't care about the ordering of directories in the
-help the case where dir A has both dir B and the root dir as parents if we
+linked-list, so we can simply leave directories in their old positions. This
-lose power inconveniently.
+does make the diagrams a bit hard to draw, but the littlefs doesn't really
 care.
-Initially, you might think this is fine. Dir A _might_ end up with two parents,
+It's also worth noting that once again we have an operation that isn't actually
-but the filesystem will still work as intended. But then this raises the
+atomic. After we add directory A to directory B, we could lose power, leaving
-question of what do we do when the dir A wears out? For other directory blocks
+directory A as a part of both the root directory and directory B. However,
-we can update the parent pointer, but for a dir with two parents we would need
+there isn't anything inherent to the littlefs that prevents a directory from
-work out how to update both parents. And the check for multiple parents would
+having multiple parents, so in this case, we just allow that to happen. Extra
-need to be carried out for every directory, even if the directory has never
+care is taken to only remove a directory from the linked-list if there are
-been moved.
+no parents left in the filesystem.
 It also presents a bad user-experience, since the condition of ending up with
 two parents is rare, it's unlikely user-level code will be prepared. Just think
 about how a user would recover from a multi-parented directory. They can't just
 remove one directory, since remove would report the directory as "not empty".
 Other atomic filesystems simple COW the entire directory tree. But this
 introduces a significant bit of complexity, which leads to code size, along
 with a surprisingly expensive runtime cost during what most users assume is
 a single pointer update.
 Another option is to update the directory block we're moving from to point
 to the destination with a sort of predicate that we have moved if the
 destination exists. Unfortunately, the omnipresent concern of wear could
 cause any of these directory entries to change blocks, and changing the
 entry size before a move introduces complications if it spills out of
 the current directory block.
 So how do we go about moving a directory atomically?
 We rely on the improbableness of power loss.
 Power loss during a move is certainly possible, but it's actually relatively
 rare. Unless a device is writing to a filesystem constantly, it's unlikely that
 a power loss will occur during filesystem activity. We still need to handle
 the condition, but runtime during a power loss takes a back seat to the runtime
 during normal operations.
 So what littlefs does is inelegantly simple. When littlefs moves a file, it
 marks the file as "moving". This is stored as a single bit in the directory
 entry and doesn't take up much space. Then littlefs moves the directory,
 finishing with the complete remove of the "moving" directory entry.
 ```
         .--------.
         |root dir|-.
         | pair 0 | |
 .--------|        |-'
 |        '--------'
 |        .-'    '-.
 |       v          v
 |  .--------.  .--------.
 '->| dir A  |->| dir B  |
   | pair 0 |  | pair 0 |
   |        |  |        |
   '--------'  '--------'
 |  update root directory to mark directory A as moving
 v
        .----------.
        |root dir  |-.
        | pair 0   | |
 .-------| moving A!|-'
 |       '----------'
 |        .-'    '-.
 |       v          v
 |  .--------.  .--------.
 '->| dir A  |->| dir B  |
   | pair 0 |  | pair 0 |
   |        |  |        |
   '--------'  '--------'
 |  update directory B to point to directory A
 v
        .----------.
        |root dir  |-.
        | pair 0   | |
 .-------| moving A!|-'
 |       '----------'
 |    .-----'    '-.
 |    |             v
 |    |           .--------.
 |    |        .->| dir B  |
 |    |        |  | pair 0 |
 |    |        |  |        |
 |    |        |  '--------'
 |    |     .-------'
 |    v    v   |
 |  .--------. |
 '->| dir A  |-'
   | pair 0 |
   |        |
   '--------'
 |  update root to no longer contain directory A
 v
     .--------.
     |root dir|-.
     | pair 0 | |
 .----|        |-'
 |    '--------'
 |        |
 |        v
 |    .--------.
 | .->| dir B  |
 | |  | pair 0 |
 | '--|        |-.
 |    '--------' |
 |        |      |
 |        v      |
 |    .--------. |
 '--->| dir A  |-'
     | pair 0 |
     |        |
     '--------'
 ```
 Now, if we run into a directory entry that has been marked as "moved", one
 of two things is possible. Either the directory entry exists elsewhere in the
 filesystem, or it doesn't. This is a O(n) operation, but only occurs in the
 unlikely case we lost power during a move.
 And we can easily fix the "moved" directory entry. Since we're already scanning
 the filesystem during the deorphan step, we can also check for moved entries.
 If we find one, we either remove the "moved" marking or remove the whole entry
 if it exists elsewhere in the filesystem.
 ## Wear awareness
 So now that we have all of the pieces of a filesystem, we can look at a more
 subtle attribute of embedded storage: The wear down of flash blocks.
-The first concern for the littlefs, is that perfectly valid blocks can suddenly
+The first concern for the littlefs, is that prefectly valid blocks can suddenly
 become unusable. As a nice side-effect of using a COW data-structure for files,
 we can simply move on to a different block when a file write fails. All
 modifications to files are performed in copies, so we will only replace the
@@ -1153,28 +906,23 @@ develops errors and needs to be moved.
 ## Wear leveling
-The second concern for the littlefs is that blocks in the filesystem may wear
+The second concern for the littlefs, is that blocks in the filesystem may wear
 unevenly. In this situation, a filesystem may meet an early demise where
-there are no more non-corrupted blocks that aren't in use. It's common to
+there are no more non-corrupted blocks that aren't in use. It may be entirely
-have files that were written once and left unmodified, wasting the potential
+possible that files were written once and left unmodified, wasting the
-erase cycles of the blocks it sits on.
+potential erase cycles of the blocks it sits on.
 Wear leveling is a term that describes distributing block writes evenly to
 avoid the early termination of a flash part. There are typically two levels
 of wear leveling:
-1. Dynamic wear leveling - Wear is distributed evenly across all **dynamic**
+1. Dynamic wear leveling - Blocks are distributed evenly during blocks writes.
-   blocks. Usually this is accomplished by simply choosing the unused block
+   Note that the issue with write-once files still exists in this case.
-   with the lowest amount of wear. Note this does not solve the problem of
+2. Static wear leveling - Unmodified blocks are evicted for new block writes.
-   static data.
+   This provides the longest lifetime for a flash device.
 2. Static wear leveling - Wear is distributed evenly across all **dynamic**
   and **static** blocks. Unmodified blocks may be evicted for new block
   writes. This does handle the problem of static data but may lead to
   wear amplification.
-In littlefs's case, it's possible to use the revision count on metadata pairs
+Now, it's possible to use the revision count on metadata pairs to approximate
-to approximate the wear of a metadata block. And combined with the COW nature
+the wear of a metadata block. And combined with the COW nature of files, the
-of files, littlefs could provide your usual implementation of dynamic wear
+littlefs could provide a form of dynamic wear leveling.
 leveling.
 However, the littlefs does not. This is for a few reasons. Most notably, even
 if the littlefs did implement dynamic wear leveling, this would still not
@@ -1185,20 +933,19 @@ As a flash device reaches the end of its life, the metadata blocks will
 naturally be the first to go since they are updated most often. In this
 situation, the littlefs is designed to simply move on to another set of
 metadata blocks. This travelling means that at the end of a flash device's
-life, the filesystem will have worn the device down nearly as evenly as the
+life, the filesystem will have worn the device down as evenly as a dynamic
-usual dynamic wear leveling could. More aggressive wear leveling would come
+wear leveling filesystem could anyways. Simply put, if the lifetime of flash
-with a code-size cost for marginal benefit.
+is a serious concern, static wear leveling is the only valid solution.
-
+This is a very important takeaway to note. If your storage stack uses highly
-One important takeaway to note, if your storage stack uses highly sensitive
+sensitive storage such as NAND flash. In most cases you are going to be better
-storage such as NAND flash, static wear leveling is the only valid solution.
+off just using a [flash translation layer (FTL)](https://en.wikipedia.org/wiki/Flash_translation_layer).
 In most cases you are going to be better off using a full [flash translation layer (FTL)](https://en.wikipedia.org/wiki/Flash_translation_layer).
 NAND flash already has many limitations that make it poorly suited for an
 embedded system: low erase cycles, very large blocks, errors that can develop
 even during reads, errors that can develop during writes of neighboring blocks.
 Managing sensitive storage such as NAND flash is out of scope for the littlefs.
 The littlefs does have some properties that may be beneficial on top of a FTL,
-such as limiting the number of writes where possible, but if you have the
+such as limiting the number of writes where possible. But if you have the
 storage requirements that necessitate the need of NAND flash, you should have
 the RAM to match and just use an FTL or flash filesystem.
@@ -1208,18 +955,18 @@ So, to summarize:
 1. The littlefs is composed of directory blocks
 2. Each directory is a linked-list of metadata pairs
-3. These metadata pairs can be updated atomically by alternating which
+3. These metadata pairs can be updated atomically by alternative which
   metadata block is active
 4. Directory blocks contain either references to other directories or files
-5. Files are represented by copy-on-write CTZ skip-lists which support O(1)
+5. Files are represented by copy-on-write CTZ linked-lists
-   append and O(n log n) reading
+6. The CTZ linked-lists support appending in O(1) and reading in O(n logn)
-6. Blocks are allocated by scanning the filesystem for used blocks in a
+7. Blocks are allocated by scanning the filesystem for used blocks in a
-   fixed-size lookahead region that is stored in a bit-vector
+   fixed-size lookahead region is that stored in a bit-vector
-7. To facilitate scanning the filesystem, all directories are part of a
+8. To facilitate scanning the filesystem, all directories are part of a
   linked-list that is threaded through the entire filesystem
-8. If a block develops an error, the littlefs allocates a new block, and
+9. If a block develops an error, the littlefs allocates a new block, and
   moves the data and references of the old block to the new.
-9. Any case where an atomic operation is not possible, mistakes are resolved
+10. Any case where an atomic operation is not possible, it is taken care of
   by a deorphan step that occurs on the first allocation after boot
 That's the little filesystem. Thanks for reading!
--- a/24
+++ b/24
@@ -1,8 +1,8 @@
 TARGET = lfs
-CC ?= gcc
+CC = gcc
-AR ?= ar
+AR = ar
-SIZE ?= size
+SIZE = size
 SRC += $(wildcard *.c emubd/*.c)
 OBJ := $(SRC:.c=.o)
@@ -11,18 +11,16 @@ ASM := $(SRC:.c=.s)
 TEST := $(patsubst tests/%.sh,%,$(wildcard tests/test_*))
 SHELL = /bin/bash -o pipefail
 ifdef DEBUG
-override CFLAGS += -O0 -g3
+CFLAGS += -O0 -g3
 else
-override CFLAGS += -Os
+CFLAGS += -Os
 endif
 ifdef WORD
-override CFLAGS += -m$(WORD)
+CFLAGS += -m$(WORD)
 endif
-override CFLAGS += -I.
+CFLAGS += -I.
-override CFLAGS += -std=c99 -Wall -pedantic
+CFLAGS += -std=c99 -Wall -pedantic
 all: $(TARGET)
@@ -33,14 +31,10 @@ size: $(OBJ)
 	$(SIZE) -t $^
 .SUFFIXES:
-test: test_format test_dirs test_files test_seek test_truncate test_parallel \
+test: test_format test_dirs test_files test_seek test_parallel \
 	test_alloc test_paths test_orphan test_move test_corrupt
 test_%: tests/test_%.sh
 ifdef QUIET
 	@./$< | sed -n '/^[-=]/p'
 else
 	./$<
 endif
 -include $(DEP)
--- a/README.md
+++ b/README.md
@@ -11,17 +11,23 @@ A little fail-safe filesystem designed for embedded systems.
   | | |
 ```
-**Bounded RAM/ROM** - The littlefs is designed to work with a limited amount
+**Fail-safe** - The littlefs is designed to work consistently with random
-of memory. Recursion is avoided and dynamic memory is limited to configurable
+power failures. During filesystem operations the storage on disk is always
-buffers that can be provided statically.
+kept in a valid state. The filesystem also has strong copy-on-write garuntees.
 When updating a file, the original file will remain unmodified until the
 file is closed, or sync is called.
-**Power-loss resilient** - The littlefs is designed for systems that may have
+**Wear awareness** - While the littlefs does not implement static wear
-random power failures. The littlefs has strong copy-on-write guarantees and
+leveling, the littlefs takes into account write errors reported by the
-storage on disk is always kept in a valid state.
+underlying block device and uses a limited form of dynamic wear leveling
 to manage blocks that go bad during the lifetime of the filesystem.
-**Wear leveling** - Since the most common form of embedded storage is erodible
+**Bounded ram/rom** - The littlefs is designed to work in a
-flash memories, littlefs provides a form of dynamic wear leveling for systems
+limited amount of memory, recursion is avoided, and dynamic memory is kept
-that can not fit a full flash translation layer.
+to a minimum. The littlefs allocates two fixed-size buffers for general
 operations, and one fixed-size buffer per file. If there is only ever one file
 in use, all memory can be provided statically and the littlefs can be used
 in a system without dynamic memory.
 ## Example
@@ -88,9 +94,9 @@ int main(void) {
 ## Usage
 Detailed documentation (or at least as much detail as is currently available)
-can be found in the comments in [lfs.h](lfs.h).
+can be cound in the comments in [lfs.h](lfs.h).
-As you may have noticed, littlefs takes in a configuration structure that
+As you may have noticed, the littlefs takes in a configuration structure that
 defines how the filesystem operates. The configuration struct provides the
 filesystem with the block device operations and dimensions, tweakable
 parameters that tradeoff memory usage for performance, and optional
@@ -98,16 +104,14 @@ static buffers if the user wants to avoid dynamic memory.
 The state of the littlefs is stored in the `lfs_t` type which is left up
 to the user to allocate, allowing multiple filesystems to be in use
-simultaneously. With the `lfs_t` and configuration struct, a user can
+simultaneously. With the `lfs_t` and configuration struct, a user can either
 format a block device or mount the filesystem.
-Once mounted, the littlefs provides a full set of POSIX-like file and
+Once mounted, the littlefs provides a full set of posix-like file and
 directory functions, with the deviation that the allocation of filesystem
-structures must be provided by the user.
+structures must be provided by the user. An important addition is that
-
+no file updates will actually be written to disk until a sync or close
-All POSIX operations, such as remove and rename, are atomic, even in event
+is called.
 of power-loss. Additionally, no file updates are actually committed to the
 filesystem until sync or close is called on the file.
 ## Other notes
@@ -115,50 +119,27 @@ All littlefs have the potential to return a negative error code. The errors
 can be either one of those found in the `enum lfs_error` in [lfs.h](lfs.h),
 or an error returned by the user's block device operations.
-In the configuration struct, the `prog` and `erase` function provided by the
+It should also be noted that the littlefs does not do anything to insure
-user may return a `LFS_ERR_CORRUPT` error if the implementation already can
+that the data written to disk is machine portable. It should be fine as
-detect corrupt blocks. However, the wear leveling does not depend on the return
+long as the machines involved share endianness and don't have really
-code of these functions, instead all data is read back and checked for
+strange padding requirements. If the question does come up, the littlefs
-integrity.
+metadata should be stored on disk in little-endian format.
-If your storage caches writes, make sure that the provided `sync` function
+## Design
 flushes all the data to memory and ensures that the next read fetches the data
 from memory, otherwise data integrity can not be guaranteed. If the `write`
 function does not perform caching, and therefore each `read` or `write` call
 hits the memory, the `sync` function can simply return 0.
-## Reference material
+the littlefs was developed with the goal of learning more about filesystem
-
+design by tackling the relative unsolved problem of managing a robust
-[DESIGN.md](DESIGN.md) - DESIGN.md contains a fully detailed dive into how
+filesystem resilient to power loss on devices with limited RAM and ROM.
-littlefs actually works. I would encourage you to read it since the
+More detail on the solutions and tradeoffs incorporated into this filesystem
-solutions and tradeoffs at work here are quite interesting.
+can be found in [DESIGN.md](DESIGN.md). The specification for the layout
-
+of the filesystem on disk can be found in [SPEC.md](SPEC.md).
 [SPEC.md](SPEC.md) - SPEC.md contains the on-disk specification of littlefs
 with all the nitty-gritty details. Can be useful for developing tooling.
 ## Testing
-The littlefs comes with a test suite designed to run on a PC using the
+The littlefs comes with a test suite designed to run on a pc using the
 [emulated block device](emubd/lfs_emubd.h) found in the emubd directory.
-The tests assume a Linux environment and can be started with make:
+The tests assume a linux environment and can be started with make:
 ``` bash
 make test
 ```
 ## Related projects
 [Mbed OS](https://github.com/ARMmbed/mbed-os/tree/master/features/filesystem/littlefs) -
 The easiest way to get started with littlefs is to jump into [Mbed](https://os.mbed.com/),
 which already has block device drivers for most forms of embedded storage. The
 littlefs is available in Mbed OS as the [LittleFileSystem](https://os.mbed.com/docs/latest/reference/littlefilesystem.html)
 class.
 [littlefs-fuse](https://github.com/geky/littlefs-fuse) - A [FUSE](https://github.com/libfuse/libfuse)
 wrapper for littlefs. The project allows you to mount littlefs directly on a
 Linux machine. Can be useful for debugging littlefs if you have an SD card
 handy.
 [littlefs-js](https://github.com/geky/littlefs-js) - A javascript wrapper for
 littlefs. I'm not sure why you would want this, but it is handy for demos.
 You can see it in action [here](http://littlefs.geky.net/demo.html).
--- a/SPEC.md
+++ b/SPEC.md
@@ -46,7 +46,7 @@ Here's the layout of metadata blocks on disk:
 | 0x04   | 32 bits       | dir size       |
 | 0x08   | 64 bits       | tail pointer   |
 | 0x10   | size-16 bytes | dir entries    |
-| 0x00+s | 32 bits       | CRC            |
+| 0x00+s | 32 bits       | crc            |
 **Revision count** - Incremented every update, only the uncorrupted
 metadata-block with the most recent revision count contains the valid metadata.
@@ -75,7 +75,7 @@ Here's an example of a simple directory stored on disk:
 (32 bits) revision count = 10                    (0x0000000a)
 (32 bits) dir size       = 154 bytes, end of dir (0x0000009a)
 (64 bits) tail pointer   = 37, 36                (0x00000025, 0x00000024)
-(32 bits) CRC            = 0xc86e3106
+(32 bits) crc            = 0xc86e3106
 00000000: 0a 00 00 00 9a 00 00 00 25 00 00 00 24 00 00 00  ........%...$...
 00000010: 22 08 00 03 05 00 00 00 04 00 00 00 74 65 61 22  "...........tea"
@@ -121,29 +121,24 @@ Here's the layout of entries on disk:
 **Entry type** - Type of the entry, currently this is limited to the following:
 - 0x11 - file entry
 - 0x22 - directory entry
- 0x2e - superblock entry
+- 0xe2 - superblock entry
-Additionally, the type is broken into two 4 bit nibbles, with the upper nibble
+Additionally, the type is broken into two 4 bit nibbles, with the lower nibble
 specifying the type's data structure used when scanning the filesystem. The
-lower nibble clarifies the type further when multiple entries share the same
+upper nibble clarifies the type further when multiple entries share the same
 data structure.
 The highest bit is reserved for marking the entry as "moved". If an entry
 is marked as "moved", the entry may also exist somewhere else in the
 filesystem. If the entry exists elsewhere, this entry must be treated as
 though it does not exist.
 **Entry length** - Length in bytes of the entry-specific data. This does
 not include the entry type size, attributes, or name. The full size in bytes
 of the entry is 4 + entry length + attribute length + name length.
 **Attribute length** - Length of system-specific attributes in bytes. Since
-attributes are system specific, there is not much guarantee on the values in
+attributes are system specific, there is not much garuntee on the values in
 this section, and systems are expected to work even when it is empty. See the
 [attributes](#entry-attributes) section for more details.
-**Name length** - Length of the entry name. Entry names are stored as UTF8,
+**Name length** - Length of the entry name. Entry names are stored as utf8,
-although most systems will probably only support ASCII. Entry names can not
+although most systems will probably only support ascii. Entry names can not
 contain '/' and can not be '.' or '..' as these are a part of the syntax of
 filesystem paths.
@@ -180,7 +175,7 @@ Here's the layout of the superblock entry:
 | offset | size                   | description                            |
 |--------|------------------------|----------------------------------------|
-| 0x00   | 8 bits                 | entry type (0x2e for superblock entry) |
+| 0x00   | 8 bits                 | entry type (0xe2 for superblock entry) |
 | 0x01   | 8 bits                 | entry length (20 bytes)                |
 | 0x02   | 8 bits                 | attribute length                       |
 | 0x03   | 8 bits                 | name length (8 bytes)                  |
@@ -213,7 +208,7 @@ Here's an example of a complete superblock:
 (32 bits) revision count   = 3                    (0x00000003)
 (32 bits) dir size         = 52 bytes, end of dir (0x00000034)
 (64 bits) tail pointer     = 3, 2                 (0x00000003, 0x00000002)
-(8 bits)  entry type       = superblock           (0x2e)
+(8 bits)  entry type       = superblock           (0xe2)
 (8 bits)  entry length     = 20 bytes             (0x14)
 (8 bits)  attribute length = 0 bytes              (0x00)
 (8 bits)  name length      = 8 bytes              (0x08)
@@ -222,10 +217,10 @@ Here's an example of a complete superblock:
 (32 bits) block count      = 1024 blocks          (0x00000400)
 (32 bits) version          = 1.1                  (0x00010001)
 (8 bytes) magic string     = littlefs
-(32 bits) CRC              = 0xc50b74fa
+(32 bits) crc              = 0xc50b74fa
 00000000: 03 00 00 00 34 00 00 00 03 00 00 00 02 00 00 00  ....4...........
-00000010: 2e 14 00 08 03 00 00 00 02 00 00 00 00 02 00 00  ................
+00000010: e2 14 00 08 03 00 00 00 02 00 00 00 00 02 00 00  ................
 00000020: 00 04 00 00 01 00 01 00 6c 69 74 74 6c 65 66 73  ........littlefs
 00000030: fa 74 0b c5                                      .t..
 ```
@@ -267,19 +262,15 @@ Here's an example of a directory entry:
 Files are stored in entries with a pointer to the head of the file and the
 size of the file. This is enough information to determine the state of the
-CTZ skip-list that is being referenced.
+CTZ linked-list that is being referenced.
 How files are actually stored on disk is a bit complicated. The full
-explanation of CTZ skip-lists can be found in [DESIGN.md](DESIGN.md#ctz-skip-lists).
+explanation of CTZ linked-lists can be found in [DESIGN.md](DESIGN.md#ctz-linked-lists).
 A terribly quick summary: For every nth block where n is divisible by 2^x,
-the block contains a pointer to block n-2^x. These pointers are stored in
+the block contains a pointer that points x blocks towards the beginning of the
-increasing order of x in each block of the file preceding the data in the
+file. These pointers are stored in order of x in each block of the file
-block.
+immediately before the data in the block.
 The maximum number of pointers in a block is bounded by the maximum file size
 divided by the block size. With 32 bits for file size, this results in a
 minimum block size of 104 bytes.
 Here's the layout of a file entry:
@@ -295,7 +286,7 @@ Here's the layout of a file entry:
 | 0xc+a  | name length bytes      | directory name                     |
 **File head** - Pointer to the block that is the head of the file's CTZ
-skip-list.
+linked-list.
 **File size** - Size of file in bytes.
--- a/emubd/lfs_emubd.c
+++ b/emubd/lfs_emubd.c
@@ -1,19 +1,8 @@
 /*
 * Block device emulated on standard files
 *
- * Copyright (c) 2017 ARM Limited
+ * Copyright (c) 2017 Christopher Haster
- *
+ * Distributed under the Apache 2.0 license
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 #include "emubd/lfs_emubd.h"
@@ -138,8 +127,8 @@ int lfs_emubd_prog(const struct lfs_config *cfg, lfs_block_t block,
    snprintf(emu->child, LFS_NAME_MAX, "%x", block);
    FILE *f = fopen(emu->path, "r+b");
-    if (!f) {
+    if (!f && errno != ENOENT) {
-        return (errno == EACCES) ? 0 : -errno;
+        return -errno;
    }
    // Check that file was erased
@@ -189,14 +178,14 @@ int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {
        return -errno;
    }
-    if (!err && S_ISREG(st.st_mode) && (S_IWUSR & st.st_mode)) {
+    if (!err && S_ISREG(st.st_mode)) {
-        err = unlink(emu->path);
+        int err = unlink(emu->path);
        if (err) {
            return -errno;
        }
    }
-    if (err || (S_ISREG(st.st_mode) && (S_IWUSR & st.st_mode))) {
+    if (err || S_ISREG(st.st_mode)) {
        FILE *f = fopen(emu->path, "w");
        if (!f) {
            return -errno;
--- a/emubd/lfs_emubd.h
+++ b/emubd/lfs_emubd.h
@@ -1,19 +1,8 @@
 /*
 * Block device emulated on standard files
 *
- * Copyright (c) 2017 ARM Limited
+ * Copyright (c) 2017 Christopher Haster
- *
+ * Distributed under the Apache 2.0 license
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 #ifndef LFS_EMUBD_H
 #define LFS_EMUBD_H
--- a/lfs.c
+++ b/lfs.c
--- a/lfs.h
+++ b/lfs.h
@@ -1,19 +1,8 @@
 /*
 * The little filesystem
 *
- * Copyright (c) 2017 ARM Limited
+ * Copyright (c) 2017 Christopher Haster
- *
+ * Distributed under the Apache 2.0 license
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 #ifndef LFS_H
 #define LFS_H
@@ -22,23 +11,6 @@
 #include <stdbool.h>
 /// Version info ///
 // Software library version
 // Major (top-nibble), incremented on backwards incompatible changes
 // Minor (bottom-nibble), incremented on feature additions
 #define LFS_VERSION 0x00010004
 #define LFS_VERSION_MAJOR (0xffff & (LFS_VERSION >> 16))
 #define LFS_VERSION_MINOR (0xffff & (LFS_VERSION >>  0))
 // Version of On-disk data structures
 // Major (top-nibble), incremented on backwards incompatible changes
 // Minor (bottom-nibble), incremented on feature additions
 #define LFS_DISK_VERSION 0x00010002
 #define LFS_DISK_VERSION_MAJOR (0xffff & (LFS_DISK_VERSION >> 16))
 #define LFS_DISK_VERSION_MINOR (0xffff & (LFS_DISK_VERSION >>  0))
 /// Definitions ///
 // Type definitions
@@ -50,78 +22,48 @@ typedef int32_t  lfs_soff_t;
 typedef uint32_t lfs_block_t;
-// Maximum inline file size in bytes. Large inline files require a larger
+// Max name size in bytes
 // read and prog cache, but if a file can be inline it does not need its own
 // data block. LFS_ATTRS_MAX + LFS_INLINE_MAX must be <= 0xffff. Stored in
 // superblock and must be respected by other littlefs drivers.
 #ifndef LFS_INLINE_MAX
 #define LFS_INLINE_MAX 0x3ff
 #endif
 // Maximum size of all attributes per file in bytes, may be redefined but a
 // a smaller LFS_ATTRS_MAX has no benefit. LFS_ATTRS_MAX + LFS_INLINE_MAX
 // must be <= 0xffff. Stored in superblock and must be respected by other
 // littlefs drivers.
 #ifndef LFS_ATTRS_MAX
 #define LFS_ATTRS_MAX 0x3f
 #endif
 // Max name size in bytes, may be redefined to reduce the size of the
 // info struct. Stored in superblock and must be respected by other
 // littlefs drivers.
 #ifndef LFS_NAME_MAX
-#define LFS_NAME_MAX 0xff
+#define LFS_NAME_MAX 255
 #endif
 // Possible error codes, these are negative to allow
 // valid positive return values
 enum lfs_error {
-    LFS_ERR_OK          = 0,    // No error
+    LFS_ERR_OK      = 0,    // No error
-    LFS_ERR_IO          = -5,   // Error during device operation
+    LFS_ERR_IO      = -5,   // Error during device operation
-    LFS_ERR_CORRUPT     = -52,  // Corrupted
+    LFS_ERR_CORRUPT = -52,  // Corrupted
-    LFS_ERR_NOENT       = -2,   // No directory entry
+    LFS_ERR_NOENT   = -2,   // No directory entry
-    LFS_ERR_EXIST       = -17,  // Entry already exists
+    LFS_ERR_EXISTS  = -17,  // Entry already exists
-    LFS_ERR_NOTDIR      = -20,  // Entry is not a dir
+    LFS_ERR_NOTDIR  = -20,  // Entry is not a dir
-    LFS_ERR_ISDIR       = -21,  // Entry is a dir
+    LFS_ERR_ISDIR   = -21,  // Entry is a dir
-    LFS_ERR_NOTEMPTY    = -39,  // Dir is not empty
+    LFS_ERR_INVAL   = -22,  // Invalid parameter
-    LFS_ERR_BADF        = -9,   // Bad file number
+    LFS_ERR_NOSPC   = -28,  // No space left on device
-    LFS_ERR_INVAL       = -22,  // Invalid parameter
+    LFS_ERR_NOMEM   = -12,  // No more memory available
    LFS_ERR_NOSPC       = -28,  // No space left on device
    LFS_ERR_NOMEM       = -12,  // No more memory available
    LFS_ERR_NAMETOOLONG = -36,  // File name too long
 };
 // File types
 enum lfs_type {
-    // file type
+    LFS_TYPE_REG        = 0x11,
-    LFS_TYPE_REG        = 0x01,
+    LFS_TYPE_DIR        = 0x22,
-    LFS_TYPE_DIR        = 0x02,
+    LFS_TYPE_SUPERBLOCK = 0x2e,
    LFS_TYPE_SUPERBLOCK = 0x0e,
    // on disk structure
    LFS_STRUCT_CTZ      = 0x10,
    LFS_STRUCT_DIR      = 0x20,
    LFS_STRUCT_INLINE   = 0x30,
    LFS_STRUCT_MOVED    = 0x80,
 };
 // File open flags
 enum lfs_open_flags {
    // open flags
-    LFS_O_RDONLY = 1,         // Open a file as read only
+    LFS_O_RDONLY = 1,        // Open a file as read only
-    LFS_O_WRONLY = 2,         // Open a file as write only
+    LFS_O_WRONLY = 2,        // Open a file as write only
-    LFS_O_RDWR   = 3,         // Open a file as read and write
+    LFS_O_RDWR   = 3,        // Open a file as read and write
-    LFS_O_CREAT  = 0x0100,    // Create a file if it does not exist
+    LFS_O_CREAT  = 0x0100,   // Create a file if it does not exist
-    LFS_O_EXCL   = 0x0200,    // Fail if a file already exists
+    LFS_O_EXCL   = 0x0200,   // Fail if a file already exists
-    LFS_O_TRUNC  = 0x0400,    // Truncate the existing file to zero size
+    LFS_O_TRUNC  = 0x0400,   // Truncate the existing file to zero size
-    LFS_O_APPEND = 0x0800,    // Move to end of file on every write
+    LFS_O_APPEND = 0x0800,   // Move to end of file on every write
    // internally used flags
-    LFS_F_DIRTY   = 0x010000, // File does not match storage
+    LFS_F_DIRTY   = 0x10000, // File does not match storage
-    LFS_F_WRITING = 0x020000, // File has been written since last flush
+    LFS_F_WRITING = 0x20000, // File has been written since last flush
-    LFS_F_READING = 0x040000, // File has been read since last flush
+    LFS_F_READING = 0x40000, // File has been read since last flush
    LFS_F_ERRED   = 0x080000, // An error occured during write
    LFS_F_INLINE  = 0x100000, // Currently inlined in directory entry
 };
 // File seek flags
@@ -145,14 +87,14 @@ struct lfs_config {
    // Program a region in a block. The block must have previously
    // been erased. Negative error codes are propogated to the user.
-    // May return LFS_ERR_CORRUPT if the block should be considered bad.
+    // The prog function must return LFS_ERR_CORRUPT if the block should
    // be considered bad.
    int (*prog)(const struct lfs_config *c, lfs_block_t block,
            lfs_off_t off, const void *buffer, lfs_size_t size);
    // Erase a block. A block must be erased before being programmed.
    // The state of an erased block is undefined. Negative error codes
    // are propogated to the user.
    // May return LFS_ERR_CORRUPT if the block should be considered bad.
    int (*erase)(const struct lfs_config *c, lfs_block_t block);
    // Sync the state of the underlying block device. Negative error codes
@@ -167,13 +109,11 @@ struct lfs_config {
    // Minimum size of a block program. This determines the size of program
    // buffers. This may be larger than the physical program size to improve
    // performance by caching more of the block device.
    // Must be a multiple of the read size.
    lfs_size_t prog_size;
    // Size of an erasable block. This does not impact ram consumption and
    // may be larger than the physical erase size. However, this should be
-    // kept small as each file currently takes up an entire block.
+    // kept small as each file currently takes up an entire block .
    // Must be a multiple of the program size.
    lfs_size_t block_size;
    // Number of erasable blocks on the device.
@@ -198,25 +138,6 @@ struct lfs_config {
    // Optional, statically allocated buffer for files. Must be program sized.
    // If enabled, only one file may be opened at a time.
    void *file_buffer;
    // Optional upper limit on inlined files in bytes. Large inline files
    // require a larger read and prog cache, but if a file can be inlined it
    // does not need its own data block. Must be smaller than the read size
    // and prog size. Defaults to min(LFS_INLINE_MAX, read_size) when zero.
    // Stored in superblock and must be respected by other littlefs drivers.
    lfs_size_t inline_size;
    // Optional upper limit on attributes per file in bytes. No downside for
    // larger attributes size but must be less than LFS_ATTRS_MAX. Defaults to
    // LFS_ATTRS_MAX when zero.Stored in superblock and must be respected by
    // other littlefs drivers.
    lfs_size_t attrs_size;
    // Optional upper limit on length of file names in bytes. No downside for
    // larger names except the size of the info struct which is controlled by
    // the LFS_NAME_MAX define. Defaults to LFS_NAME_MAX when zero. Stored in
    // superblock and must be respected by other littlefs drivers.
    lfs_size_t name_size;
 };
@@ -236,7 +157,6 @@ struct lfs_info {
 /// littlefs data structures ///
 typedef struct lfs_entry {
    lfs_off_t off;
    lfs_size_t size;
    struct lfs_disk_entry {
        uint8_t type;
@@ -268,7 +188,6 @@ typedef struct lfs_file {
    lfs_size_t size;
    uint32_t flags;
    lfs_size_t inline_size;
    lfs_off_t pos;
    lfs_block_t block;
    lfs_off_t off;
@@ -276,7 +195,6 @@ typedef struct lfs_file {
 } lfs_file_t;
 typedef struct lfs_dir {
    struct lfs_dir *next;
    lfs_block_t pair[2];
    lfs_off_t off;
@@ -291,24 +209,26 @@ typedef struct lfs_dir {
 } lfs_dir_t;
 typedef struct lfs_superblock {
    lfs_off_t off;
    struct lfs_disk_superblock {
        uint8_t type;
        uint8_t elen;
        uint8_t alen;
        uint8_t nlen;
        lfs_block_t root[2];
-
+        uint32_t block_size;
-        lfs_size_t block_size;
+        uint32_t block_count;
        lfs_size_t block_count;
        uint32_t version;
-
+        char magic[8];
        lfs_size_t inline_size;
        lfs_size_t attrs_size;
        lfs_size_t name_size;
    } d;
 } lfs_superblock_t;
 typedef struct lfs_free {
    lfs_size_t lookahead;
    lfs_block_t begin;
-    lfs_block_t size;
+    lfs_block_t end;
    lfs_block_t off;
    lfs_block_t ack;
    uint32_t *buffer;
 } lfs_free_t;
@@ -318,17 +238,13 @@ typedef struct lfs {
    lfs_block_t root[2];
    lfs_file_t *files;
    lfs_dir_t *dirs;
    lfs_cache_t rcache;
    lfs_cache_t pcache;
    lfs_free_t free;
-    bool deorphaned;
+    uint8_t unstable;
-
+    uint8_t sum;
    lfs_size_t inline_size;
    lfs_size_t attrs_size;
    lfs_size_t name_size;
 } lfs_t;
@@ -433,11 +349,6 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
 lfs_soff_t lfs_file_seek(lfs_t *lfs, lfs_file_t *file,
        lfs_soff_t off, int whence);
 // Truncates the size of the file to the specified size
 //
 // Returns a negative error code on failure.
 int lfs_file_truncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size);
 // Return the position of the file
 //
 // Equivalent to lfs_file_seek(lfs, file, 0, LFS_SEEK_CUR)
@@ -524,5 +435,8 @@ int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data);
 // Returns a negative error code on failure.
 int lfs_deorphan(lfs_t *lfs);
 // TODO doc
 int lfs_deduplicate(lfs_t *lfs);
 #endif
--- a/lfs_util.c
+++ b/lfs_util.c
@@ -1,27 +1,12 @@
 /*
 * lfs util functions
 *
- * Copyright (c) 2017 ARM Limited
+ * Copyright (c) 2017 Christopher Haster
- *
+ * Distributed under the Apache 2.0 license
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 #include "lfs_util.h"
 // Only compile if user does not provide custom config
 #ifndef LFS_CONFIG
 // Software CRC implementation with small lookup table
 void lfs_crc(uint32_t *restrict crc, const void *buffer, size_t size) {
    static const uint32_t rtable[16] = {
        0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
@@ -38,5 +23,3 @@ void lfs_crc(uint32_t *restrict crc, const void *buffer, size_t size) {
    }
 }
 #endif
--- a/lfs_util.h
+++ b/lfs_util.h
@@ -1,90 +1,19 @@
 /*
 * lfs utility functions
 *
- * Copyright (c) 2017 ARM Limited
+ * Copyright (c) 2017 Christopher Haster
- *
+ * Distributed under the Apache 2.0 license
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 #ifndef LFS_UTIL_H
 #define LFS_UTIL_H
 // Users can override lfs_util.h with their own configuration by defining
 // LFS_CONFIG as a header file to include (-DLFS_CONFIG=lfs_config.h).
 //
 // If LFS_CONFIG is used, none of the default utils will be emitted and must be
 // provided by the config file. To start I would suggest copying lfs_util.h and
 // modifying as needed.
 #ifdef LFS_CONFIG
 #define LFS_STRINGIZE(x) LFS_STRINGIZE2(x)
 #define LFS_STRINGIZE2(x) #x
 #include LFS_STRINGIZE(LFS_CONFIG)
 #else
 // System includes
 #include <stdint.h>
 #include <stdbool.h>
 #include <string.h>
 #ifndef LFS_NO_MALLOC
 #include <stdlib.h>
-#endif
+#include <stdint.h>
 #ifndef LFS_NO_ASSERT
 #include <assert.h>
 #endif
 #if !defined(LFS_NO_DEBUG) || !defined(LFS_NO_WARN) || !defined(LFS_NO_ERROR)
 #include <stdio.h>
 #endif
-// Macros, may be replaced by system specific wrappers. Arguments to these
+// Builtin functions, these may be replaced by more
-// macros must not have side-effects as the macros can be removed for a smaller
+// efficient implementations in the system
 // code footprint
 // Logging functions
 #ifndef LFS_NO_DEBUG
 #define LFS_DEBUG(fmt, ...) \
    printf("lfs debug:%d: " fmt "\n", __LINE__, __VA_ARGS__)
 #else
 #define LFS_DEBUG(fmt, ...)
 #endif
 #ifndef LFS_NO_WARN
 #define LFS_WARN(fmt, ...) \
    printf("lfs warn:%d: " fmt "\n", __LINE__, __VA_ARGS__)
 #else
 #define LFS_WARN(fmt, ...)
 #endif
 #ifndef LFS_NO_ERROR
 #define LFS_ERROR(fmt, ...) \
    printf("lfs error:%d: " fmt "\n", __LINE__, __VA_ARGS__)
 #else
 #define LFS_ERROR(fmt, ...)
 #endif
 // Runtime assertions
 #ifndef LFS_NO_ASSERT
 #define LFS_ASSERT(test) assert(test)
 #else
 #define LFS_ASSERT(test)
 #endif
 // Builtin functions, these may be replaced by more efficient
 // toolchain-specific implementations. LFS_NO_INTRINSICS falls back to a more
 // expensive basic C implementation for debugging purposes
 // Min/max functions for unsigned 32-bit numbers
 static inline uint32_t lfs_max(uint32_t a, uint32_t b) {
    return (a > b) ? a : b;
 }
@@ -93,93 +22,27 @@ static inline uint32_t lfs_min(uint32_t a, uint32_t b) {
    return (a < b) ? a : b;
 }
 // Find the next smallest power of 2 less than or equal to a
 static inline uint32_t lfs_npw2(uint32_t a) {
 #if !defined(LFS_NO_INTRINSICS) && (defined(__GNUC__) || defined(__CC_ARM))
    return 32 - __builtin_clz(a-1);
 #else
    uint32_t r = 0;
    uint32_t s;
    a -= 1;
    s = (a > 0xffff) << 4; a >>= s; r |= s;
    s = (a > 0xff  ) << 3; a >>= s; r |= s;
    s = (a > 0xf   ) << 2; a >>= s; r |= s;
    s = (a > 0x3   ) << 1; a >>= s; r |= s;
    return (r | (a >> 1)) + 1;
 #endif
 }
 // Count the number of trailing binary zeros in a
 // lfs_ctz(0) may be undefined
 static inline uint32_t lfs_ctz(uint32_t a) {
 #if !defined(LFS_NO_INTRINSICS) && defined(__GNUC__)
    return __builtin_ctz(a);
 #else
    return lfs_npw2((a & -a) + 1) - 1;
 #endif
 }
-// Count the number of binary ones in a
+static inline uint32_t lfs_npw2(uint32_t a) {
-static inline uint32_t lfs_popc(uint32_t a) {
+    return 32 - __builtin_clz(a-1);
 #if !defined(LFS_NO_INTRINSICS) && (defined(__GNUC__) || defined(__CC_ARM))
    return __builtin_popcount(a);
 #else
    a = a - ((a >> 1) & 0x55555555);
    a = (a & 0x33333333) + ((a >> 2) & 0x33333333);
    return (((a + (a >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
 #endif
 }
 // Find the sequence comparison of a and b, this is the distance
 // between a and b ignoring overflow
 static inline int lfs_scmp(uint32_t a, uint32_t b) {
    return (int)(unsigned)(a - b);
 }
-// Convert from 32-bit little-endian to native order
+// CRC-32 with polynomial = 0x04c11db7
 static inline uint32_t lfs_fromle32(uint32_t a) {
 #if !defined(LFS_NO_INTRINSICS) && ( \
    (defined(  BYTE_ORDER  ) &&   BYTE_ORDER   ==   ORDER_LITTLE_ENDIAN  ) || \
    (defined(__BYTE_ORDER  ) && __BYTE_ORDER   == __ORDER_LITTLE_ENDIAN  ) || \
    (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__))
    return a;
 #elif !defined(LFS_NO_INTRINSICS) && ( \
    (defined(  BYTE_ORDER  ) &&   BYTE_ORDER   ==   ORDER_BIG_ENDIAN  ) || \
    (defined(__BYTE_ORDER  ) && __BYTE_ORDER   == __ORDER_BIG_ENDIAN  ) || \
    (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__))
    return __builtin_bswap32(a);
 #else
    return (((uint8_t*)&a)[0] <<  0) |
           (((uint8_t*)&a)[1] <<  8) |
           (((uint8_t*)&a)[2] << 16) |
           (((uint8_t*)&a)[3] << 24);
 #endif
 }
 // Convert to 32-bit little-endian from native order
 static inline uint32_t lfs_tole32(uint32_t a) {
    return lfs_fromle32(a);
 }
 // Calculate CRC-32 with polynomial = 0x04c11db7
 void lfs_crc(uint32_t *crc, const void *buffer, size_t size);
 // Allocate memory, only used if buffers are not provided to littlefs
 static inline void *lfs_malloc(size_t size) {
 #ifndef LFS_NO_MALLOC
    return malloc(size);
 #else
    return NULL;
 #endif
 }
-// Deallocate memory, only used if buffers are not provided to littlefs
+// Logging functions, these may be replaced by system-specific
-static inline void lfs_free(void *p) {
+// logging functions
-#ifndef LFS_NO_MALLOC
+#define LFS_DEBUG(fmt, ...) printf("lfs debug: " fmt "\n", __VA_ARGS__)
-    free(p);
+#define LFS_WARN(fmt, ...)  printf("lfs warn: " fmt "\n", __VA_ARGS__)
-#endif
+#define LFS_ERROR(fmt, ...) printf("lfs error: " fmt "\n", __VA_ARGS__)
 }
 #endif
 #endif
--- a/tests/template.fmt
+++ b/tests/template.fmt
@@ -7,11 +7,11 @@
 // test stuff
-static void test_log(const char *s, uintmax_t v) {{
+void test_log(const char *s, uintmax_t v) {{
    printf("%s: %jd\n", s, v);
 }}
-static void test_assert(const char *file, unsigned line,
+void test_assert(const char *file, unsigned line,
        const char *s, uintmax_t v, uintmax_t e) {{
    static const char *last[6] = {{0, 0}};
    if (v != e || !(last[0] == s || last[1] == s ||
@@ -37,8 +37,7 @@ static void test_assert(const char *file, unsigned line,
 // utility functions for traversals
-static int __attribute__((used)) test_count(void *p, lfs_block_t b) {{
+int test_count(void *p, lfs_block_t b) {{
    (void)b;
    unsigned *u = (unsigned*)p;
    *u += 1;
    return 0;
@@ -59,7 +58,7 @@ lfs_size_t size;
 lfs_size_t wsize;
 lfs_size_t rsize;
-uintmax_t test;
+uintmax_t res;
 #ifndef LFS_READ_SIZE
 #define LFS_READ_SIZE 16
@@ -97,7 +96,7 @@ const struct lfs_config cfg = {{
 // Entry point
-int main(void) {{
+int main() {{
    lfs_emubd_create(&cfg, "blocks");
 {tests}
--- a/tests/test.py
+++ b/tests/test.py
@@ -14,34 +14,22 @@ def generate(test):
        match = re.match('(?: *\n)*( *)(.*)=>(.*);', line, re.DOTALL | re.MULTILINE)
        if match:
            tab, test, expect = match.groups()
-            lines.append(tab+'test = {test};'.format(test=test.strip()))
+            lines.append(tab+'res = {test};'.format(test=test.strip()))
-            lines.append(tab+'test_assert("{name}", test, {expect});'.format(
+            lines.append(tab+'test_assert("{name}", res, {expect});'.format(
                    name = re.match('\w*', test.strip()).group(),
                    expect = expect.strip()))
        else:
            lines.append(line)
    # Create test file
    with open('test.c', 'w') as file:
        file.write(template.format(tests='\n'.join(lines)))
    # Remove build artifacts to force rebuild
    try:
        os.remove('test.o')
        os.remove('lfs')
    except OSError:
        pass
 def compile():
-    subprocess.check_call([
+    os.environ['CFLAGS'] = os.environ.get('CFLAGS', '') + ' -Werror'
-            os.environ.get('MAKE', 'make'),
+    subprocess.check_call(['make', '--no-print-directory', '-s'], env=os.environ)
            '--no-print-directory', '-s'])
 def execute():
-    if 'EXEC' in os.environ:
+    subprocess.check_call(["./lfs"])
        subprocess.check_call([os.environ['EXEC'], "./lfs"])
    else:
        subprocess.check_call(["./lfs"])
 def main(test=None):
    if test and not test.startswith('-'):
--- a/tests/test_alloc.sh
+++ b/tests/test_alloc.sh
@@ -121,7 +121,6 @@ tests/test.py << TEST
    size = strlen("exhaustion");
    memcpy(buffer, "exhaustion", size);
    lfs_file_write(&lfs, &file[0], buffer, size) => size;
    lfs_file_sync(&lfs, &file[0]) => 0;
    size = strlen("blahblahblahblah");
    memcpy(buffer, "blahblahblahblah", size);
@@ -143,7 +142,6 @@ tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_RDONLY);
    size = strlen("exhaustion");
    lfs_file_size(&lfs, &file[0]) => size;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "exhaustion", size) => 0;
    lfs_file_close(&lfs, &file[0]) => 0;
@@ -168,7 +166,6 @@ tests/test.py << TEST
    size = strlen("exhaustion");
    memcpy(buffer, "exhaustion", size);
    lfs_file_write(&lfs, &file[0], buffer, size) => size;
    lfs_file_sync(&lfs, &file[0]) => 0;
    size = strlen("blahblahblahblah");
    memcpy(buffer, "blahblahblahblah", size);
@@ -190,7 +187,6 @@ tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_RDONLY);
    size = strlen("exhaustion");
    lfs_file_size(&lfs, &file[0]) => size;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "exhaustion", size) => 0;
    lfs_file_close(&lfs, &file[0]) => 0;
@@ -200,14 +196,14 @@ TEST
 echo "--- Dir exhaustion test ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_stat(&lfs, "exhaustion", &info) => 0;
    lfs_size_t fullsize = info.size;
    lfs_remove(&lfs, "exhaustion") => 0;
    lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_WRONLY | LFS_O_CREAT);
    size = strlen("blahblahblahblah");
    memcpy(buffer, "blahblahblahblah", size);
-    for (lfs_size_t i = 0;
+    for (lfs_size_t i = 0; i < fullsize - 2*512; i += size) {
            i < (cfg.block_count-6)*(cfg.block_size-8);
            i += size) {
        lfs_file_write(&lfs, &file[0], buffer, size) => size;
    }
    lfs_file_close(&lfs, &file[0]) => 0;
@@ -218,11 +214,7 @@ tests/test.py << TEST
    lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_WRONLY | LFS_O_APPEND);
    size = strlen("blahblahblahblah");
    memcpy(buffer, "blahblahblahblah", size);
-    for (lfs_size_t i = 0;
+    lfs_file_write(&lfs, &file[0], buffer, size) => size;
            i < (cfg.block_size-8);
            i += size) {
        lfs_file_write(&lfs, &file[0], buffer, size) => size;
    }
    lfs_file_close(&lfs, &file[0]) => 0;
    lfs_mkdir(&lfs, "exhaustiondir") => LFS_ERR_NOSPC;
@@ -232,14 +224,14 @@ TEST
 echo "--- Chained dir exhaustion test ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
-    lfs_remove(&lfs, "exhaustion") => 0;
+    lfs_stat(&lfs, "exhaustion", &info) => 0;
    lfs_size_t fullsize = info.size;
    lfs_remove(&lfs, "exhaustion") => 0;
    lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_WRONLY | LFS_O_CREAT);
    size = strlen("blahblahblahblah");
    memcpy(buffer, "blahblahblahblah", size);
-    for (lfs_size_t i = 0;
+    for (lfs_size_t i = 0; i < fullsize - 19*512; i += size) {
            i < (cfg.block_count-24)*(cfg.block_size-8);
            i += size) {
        lfs_file_write(&lfs, &file[0], buffer, size) => size;
    }
    lfs_file_close(&lfs, &file[0]) => 0;
@@ -255,9 +247,7 @@ tests/test.py << TEST
    lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_WRONLY | LFS_O_CREAT);
    size = strlen("blahblahblahblah");
    memcpy(buffer, "blahblahblahblah", size);
-    for (lfs_size_t i = 0;
+    for (lfs_size_t i = 0; i < fullsize - 20*512; i += size) {
            i < (cfg.block_count-26)*(cfg.block_size-8);
            i += size) {
        lfs_file_write(&lfs, &file[0], buffer, size) => size;
    }
    lfs_file_close(&lfs, &file[0]) => 0;
@@ -266,46 +256,6 @@ tests/test.py << TEST
    lfs_mkdir(&lfs, "exhaustiondir2") => LFS_ERR_NOSPC;
 TEST
 echo "--- Split dir test ---"
 rm -rf blocks
 tests/test.py << TEST
    lfs_format(&lfs, &cfg) => 0;
 TEST
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    // create one block hole for half a directory
    lfs_file_open(&lfs, &file[0], "bump", LFS_O_WRONLY | LFS_O_CREAT) => 0;
    for (lfs_size_t i = 0; i < cfg.block_size; i += 2) {
        memcpy(&buffer[i], "hi", 2);
    }
    lfs_file_write(&lfs, &file[0], buffer, cfg.block_size) => cfg.block_size;
    lfs_file_close(&lfs, &file[0]) => 0;
    lfs_file_open(&lfs, &file[0], "exhaustion", LFS_O_WRONLY | LFS_O_CREAT);
    size = strlen("blahblahblahblah");
    memcpy(buffer, "blahblahblahblah", size);
    for (lfs_size_t i = 0;
            i < (cfg.block_count-6)*(cfg.block_size-8);
            i += size) {
        lfs_file_write(&lfs, &file[0], buffer, size) => size;
    }
    lfs_file_close(&lfs, &file[0]) => 0;
    // open hole
    lfs_remove(&lfs, "bump") => 0;
    lfs_mkdir(&lfs, "splitdir") => 0;
    lfs_file_open(&lfs, &file[0], "splitdir/bump",
            LFS_O_WRONLY | LFS_O_CREAT) => 0;
    for (lfs_size_t i = 0; i < cfg.block_size; i += 2) {
        memcpy(&buffer[i], "hi", 2);
    }
    lfs_file_write(&lfs, &file[0], buffer, cfg.block_size) => LFS_ERR_NOSPC;
    lfs_file_close(&lfs, &file[0]) => 0;
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Results ---"
 tests/stats.py
--- a/tests/test_corrupt.sh
+++ b/tests/test_corrupt.sh
@@ -73,7 +73,7 @@ lfs_mktree
 lfs_chktree
 echo "--- Block corruption ---"
-for i in {2..33}
+for i in {0..33}
 do 
    rm -rf blocks
    mkdir blocks
@@ -82,17 +82,6 @@ do
    lfs_chktree
 done
 echo "--- Block persistance ---"
 for i in {2..33}
 do 
    rm -rf blocks
    mkdir blocks
    lfs_mktree
    chmod a-w blocks/$(printf '%x' $i) || true
    lfs_mktree
    lfs_chktree
 done
 echo "--- Big region corruption ---"
 rm -rf blocks
 mkdir blocks
--- a/tests/test_dirs.sh
+++ b/tests/test_dirs.sh
@@ -56,7 +56,7 @@ TEST
 echo "--- Directory failures ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
-    lfs_mkdir(&lfs, "potato") => LFS_ERR_EXIST;
+    lfs_mkdir(&lfs, "potato") => LFS_ERR_EXISTS;
    lfs_dir_open(&lfs, &dir[0], "tomato") => LFS_ERR_NOENT;
    lfs_dir_open(&lfs, &dir[0], "burito") => LFS_ERR_NOTDIR;
    lfs_file_open(&lfs, &file[0], "tomato", LFS_O_RDONLY) => LFS_ERR_NOENT;
@@ -118,7 +118,6 @@ tests/test.py << TEST
        sprintf((char*)buffer, "test%d", i);
        lfs_dir_read(&lfs, &dir[0], &info) => 1;
        strcmp(info.name, (char*)buffer) => 0;
        info.type => LFS_TYPE_DIR;
    }
    lfs_dir_read(&lfs, &dir[0], &info) => 0;
    lfs_unmount(&lfs) => 0;
@@ -127,7 +126,7 @@ TEST
 echo "--- Directory remove ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
-    lfs_remove(&lfs, "potato") => LFS_ERR_NOTEMPTY;
+    lfs_remove(&lfs, "potato") => LFS_ERR_INVAL;
    lfs_remove(&lfs, "potato/sweet") => 0;
    lfs_remove(&lfs, "potato/baked") => 0;
    lfs_remove(&lfs, "potato/fried") => 0;
@@ -221,7 +220,7 @@ tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_mkdir(&lfs, "warmpotato") => 0;
    lfs_mkdir(&lfs, "warmpotato/mushy") => 0;
-    lfs_rename(&lfs, "hotpotato", "warmpotato") => LFS_ERR_NOTEMPTY;
+    lfs_rename(&lfs, "hotpotato", "warmpotato") => LFS_ERR_INVAL;
    lfs_remove(&lfs, "warmpotato/mushy") => 0;
    lfs_rename(&lfs, "hotpotato", "warmpotato") => 0;
@@ -256,7 +255,7 @@ tests/test.py << TEST
    lfs_rename(&lfs, "warmpotato/baked", "coldpotato/baked") => 0;
    lfs_rename(&lfs, "warmpotato/sweet", "coldpotato/sweet") => 0;
    lfs_rename(&lfs, "warmpotato/fried", "coldpotato/fried") => 0;
-    lfs_remove(&lfs, "coldpotato") => LFS_ERR_NOTEMPTY;
+    lfs_remove(&lfs, "coldpotato") => LFS_ERR_INVAL;
    lfs_remove(&lfs, "warmpotato") => 0;
    lfs_unmount(&lfs) => 0;
 TEST
@@ -283,53 +282,10 @@ tests/test.py << TEST
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Recursive remove ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_remove(&lfs, "coldpotato") => LFS_ERR_NOTEMPTY;
    lfs_dir_open(&lfs, &dir[0], "coldpotato") => 0;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    while (true) {
        int err = lfs_dir_read(&lfs, &dir[0], &info);
        err >= 0 => 1;
        if (err == 0) {
            break;
        }
        strcpy((char*)buffer, "coldpotato/");
        strcat((char*)buffer, info.name);
        lfs_remove(&lfs, (char*)buffer) => 0;
    }
    lfs_remove(&lfs, "coldpotato") => 0;
 TEST
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_dir_open(&lfs, &dir[0], "/") => 0;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, ".") => 0;
    info.type => LFS_TYPE_DIR;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "..") => 0;
    info.type => LFS_TYPE_DIR;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "burito") => 0;
    info.type => LFS_TYPE_REG;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "cactus") => 0;
    info.type => LFS_TYPE_DIR;
    lfs_dir_read(&lfs, &dir[0], &info) => 0;
    lfs_dir_close(&lfs, &dir[0]) => 0;
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Multi-block remove ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
-    lfs_remove(&lfs, "cactus") => LFS_ERR_NOTEMPTY;
+    lfs_remove(&lfs, "cactus") => LFS_ERR_INVAL;
    for (int i = 0; i < $LARGESIZE; i++) {
        sprintf((char*)buffer, "cactus/test%d", i);
@@ -351,71 +307,9 @@ tests/test.py << TEST
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "burito") => 0;
    info.type => LFS_TYPE_REG;
    lfs_dir_read(&lfs, &dir[0], &info) => 0;
    lfs_dir_close(&lfs, &dir[0]) => 0;
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Multi-block directory with files ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_mkdir(&lfs, "prickly-pear") => 0;
    for (int i = 0; i < $LARGESIZE; i++) {
        sprintf((char*)buffer, "prickly-pear/test%d", i);
        lfs_file_open(&lfs, &file[0], (char*)buffer,
                LFS_O_WRONLY | LFS_O_CREAT) => 0;
        size = 6;
        memcpy(wbuffer, "Hello", size);
        lfs_file_write(&lfs, &file[0], wbuffer, size) => size;
        lfs_file_close(&lfs, &file[0]) => 0;
    }
    lfs_unmount(&lfs) => 0;
 TEST
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_dir_open(&lfs, &dir[0], "prickly-pear") => 0;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
-    strcmp(info.name, ".") => 0;
+    strcmp(info.name, "coldpotato") => 0;
    info.type => LFS_TYPE_DIR;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "..") => 0;
    info.type => LFS_TYPE_DIR;
    for (int i = 0; i < $LARGESIZE; i++) {
        sprintf((char*)buffer, "test%d", i);
        lfs_dir_read(&lfs, &dir[0], &info) => 1;
        strcmp(info.name, (char*)buffer) => 0;
        info.type => LFS_TYPE_REG;
        info.size => 6;
    }
    lfs_dir_read(&lfs, &dir[0], &info) => 0;
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Multi-block remove with files ---"
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_remove(&lfs, "prickly-pear") => LFS_ERR_NOTEMPTY;
    for (int i = 0; i < $LARGESIZE; i++) {
        sprintf((char*)buffer, "prickly-pear/test%d", i);
        lfs_remove(&lfs, (char*)buffer) => 0;
    }
    lfs_remove(&lfs, "prickly-pear") => 0;
    lfs_unmount(&lfs) => 0;
 TEST
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_dir_open(&lfs, &dir[0], "/") => 0;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, ".") => 0;
    info.type => LFS_TYPE_DIR;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "..") => 0;
    info.type => LFS_TYPE_DIR;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "burito") => 0;
    info.type => LFS_TYPE_REG;
    lfs_dir_read(&lfs, &dir[0], &info) => 0;
    lfs_dir_close(&lfs, &dir[0]) => 0;
    lfs_unmount(&lfs) => 0;
--- a/tests/test_files.sh
+++ b/tests/test_files.sh
@@ -34,8 +34,7 @@ tests/test.py << TEST
    lfs_size_t chunk = 31;
    srand(0);
    lfs_mount(&lfs, &cfg) => 0;
-    lfs_file_open(&lfs, &file[0], "$2",
+    lfs_file_open(&lfs, &file[0], "$2", LFS_O_WRONLY | LFS_O_CREAT) => 0;
        ${3:-LFS_O_WRONLY | LFS_O_CREAT | LFS_O_TRUNC}) => 0;
    for (lfs_size_t i = 0; i < size; i += chunk) {
        chunk = (chunk < size - i) ? chunk : size - i;
        for (lfs_size_t b = 0; b < chunk; b++) {
@@ -54,10 +53,7 @@ tests/test.py << TEST
    lfs_size_t chunk = 29;
    srand(0);
    lfs_mount(&lfs, &cfg) => 0;
-    lfs_stat(&lfs, "$2", &info) => 0;
+    lfs_file_open(&lfs, &file[0], "$2", LFS_O_RDONLY) => 0;
    info.type => LFS_TYPE_REG;
    info.size => size;
    lfs_file_open(&lfs, &file[0], "$2", ${3:-LFS_O_RDONLY}) => 0;
    for (lfs_size_t i = 0; i < size; i += chunk) {
        chunk = (chunk < size - i) ? chunk : size - i;
        lfs_file_read(&lfs, &file[0], buffer, chunk) => chunk;
@@ -82,27 +78,10 @@ echo "--- Large file test ---"
 w_test $LARGESIZE largeavacado
 r_test $LARGESIZE largeavacado
 echo "--- Zero file test ---"
 w_test 0 noavacado
 r_test 0 noavacado
 echo "--- Truncate small test ---"
 w_test $SMALLSIZE mediumavacado
 r_test $SMALLSIZE mediumavacado
 w_test $MEDIUMSIZE mediumavacado
 r_test $MEDIUMSIZE mediumavacado
 echo "--- Truncate zero test ---"
 w_test $SMALLSIZE noavacado
 r_test $SMALLSIZE noavacado
 w_test 0 noavacado
 r_test 0 noavacado
 echo "--- Non-overlap check ---"
 r_test $SMALLSIZE smallavacado
 r_test $MEDIUMSIZE mediumavacado
 r_test $LARGESIZE largeavacado
 r_test 0 noavacado
 echo "--- Dir check ---"
 tests/test.py << TEST
@@ -126,33 +105,10 @@ tests/test.py << TEST
    strcmp(info.name, "largeavacado") => 0;
    info.type => LFS_TYPE_REG;
    info.size => $LARGESIZE;
    lfs_dir_read(&lfs, &dir[0], &info) => 1;
    strcmp(info.name, "noavacado") => 0;
    info.type => LFS_TYPE_REG;
    info.size => 0;
    lfs_dir_read(&lfs, &dir[0], &info) => 0;
    lfs_dir_close(&lfs, &dir[0]) => 0;
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Many file test ---"
 tests/test.py << TEST
    lfs_format(&lfs, &cfg) => 0;
 TEST
 tests/test.py << TEST
    // Create 300 files of 6 bytes
    lfs_mount(&lfs, &cfg) => 0;
    lfs_mkdir(&lfs, "directory") => 0;
    for (unsigned i = 0; i < 300; i++) {
        snprintf((char*)buffer, sizeof(buffer), "file_%03d", i);
        lfs_file_open(&lfs, &file[0], (char*)buffer, LFS_O_WRONLY | LFS_O_CREAT) => 0;
        size = 6;
        memcpy(wbuffer, "Hello", size);
        lfs_file_write(&lfs, &file[0], wbuffer, size) => size;
        lfs_file_close(&lfs, &file[0]) => 0;
    }
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Results ---"
 tests/stats.py
--- a/tests/test_format.sh
+++ b/tests/test_format.sh
@@ -30,10 +30,20 @@ echo "--- Invalid mount ---"
 tests/test.py << TEST
    lfs_format(&lfs, &cfg) => 0;
 TEST
-rm -f blocks/0 blocks/1
+rm blocks/0 blocks/1
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => LFS_ERR_CORRUPT;
 TEST
 echo "--- Valid corrupt mount ---"
 tests/test.py << TEST
    lfs_format(&lfs, &cfg) => 0;
 TEST
 rm blocks/0
 tests/test.py << TEST
    lfs_mount(&lfs, &cfg) => 0;
    lfs_unmount(&lfs) => 0;
 TEST
 echo "--- Results ---"
 tests/stats.py
--- a/tests/test_paths.sh
+++ b/tests/test_paths.sh
@@ -108,10 +108,6 @@ tests/test.py << TEST
    lfs_stat(&lfs, "/", &info) => 0;
    info.type => LFS_TYPE_DIR;
    strcmp(info.name, "/") => 0;
    lfs_mkdir(&lfs, "/") => LFS_ERR_EXIST;
    lfs_file_open(&lfs, &file[0], "/", LFS_O_WRONLY | LFS_O_CREAT)
        => LFS_ERR_ISDIR;
    lfs_unmount(&lfs) => 0;
 TEST
--- a/tests/test_seek.sh
+++ b/tests/test_seek.sh
@@ -133,14 +133,6 @@ tests/test.py << TEST
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
    lfs_file_seek(&lfs, &file[0], 0, LFS_SEEK_CUR) => size;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
    lfs_file_seek(&lfs, &file[0], size, LFS_SEEK_CUR) => 3*size;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
    lfs_file_seek(&lfs, &file[0], pos, LFS_SEEK_SET) => pos;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
@@ -182,14 +174,6 @@ tests/test.py << TEST
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
    lfs_file_seek(&lfs, &file[0], 0, LFS_SEEK_CUR) => size;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
    lfs_file_seek(&lfs, &file[0], size, LFS_SEEK_CUR) => 3*size;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
    lfs_file_seek(&lfs, &file[0], pos, LFS_SEEK_SET) => pos;
    lfs_file_read(&lfs, &file[0], buffer, size) => size;
    memcmp(buffer, "kittycatcat", size) => 0;
--- a/tests/test_truncate.sh
+++ b/tests/test_truncate.sh
@@ -1,158 +0,0 @@
 #!/bin/bash
 set -eu
 SMALLSIZE=32
 MEDIUMSIZE=2048
 LARGESIZE=8192
 echo "=== Truncate tests ==="
 rm -rf blocks
 tests/test.py << TEST
    lfs_format(&lfs, &cfg) => 0;
 TEST
 truncate_test() {
 STARTSIZES="$1"
 STARTSEEKS="$2"
 HOTSIZES="$3"
 COLDSIZES="$4"
 tests/test.py << TEST
    static const lfs_off_t startsizes[] = {$STARTSIZES};
    static const lfs_off_t startseeks[] = {$STARTSEEKS};
    static const lfs_off_t hotsizes[]   = {$HOTSIZES};
    lfs_mount(&lfs, &cfg) => 0;
    for (int i = 0; i < sizeof(startsizes)/sizeof(startsizes[0]); i++) {
        sprintf((char*)buffer, "hairyhead%d", i);
        lfs_file_open(&lfs, &file[0], (const char*)buffer,
                LFS_O_WRONLY | LFS_O_CREAT | LFS_O_TRUNC) => 0;
        strcpy((char*)buffer, "hair");
        size = strlen((char*)buffer);
        for (int j = 0; j < startsizes[i]; j += size) {
            lfs_file_write(&lfs, &file[0], buffer, size) => size;
        }
        lfs_file_size(&lfs, &file[0]) => startsizes[i];
        if (startseeks[i] != startsizes[i]) {
            lfs_file_seek(&lfs, &file[0],
                    startseeks[i], LFS_SEEK_SET) => startseeks[i];
        }
        lfs_file_truncate(&lfs, &file[0], hotsizes[i]) => 0;
        lfs_file_size(&lfs, &file[0]) => hotsizes[i];
        lfs_file_close(&lfs, &file[0]) => 0;
    }
    lfs_unmount(&lfs) => 0;
 TEST
 tests/test.py << TEST
    static const lfs_off_t startsizes[] = {$STARTSIZES};
    static const lfs_off_t hotsizes[]   = {$HOTSIZES};
    static const lfs_off_t coldsizes[]  = {$COLDSIZES};
    lfs_mount(&lfs, &cfg) => 0;
    for (int i = 0; i < sizeof(startsizes)/sizeof(startsizes[0]); i++) {
        sprintf((char*)buffer, "hairyhead%d", i);
        lfs_file_open(&lfs, &file[0], (const char*)buffer, LFS_O_RDWR) => 0;
        lfs_file_size(&lfs, &file[0]) => hotsizes[i];
        size = strlen("hair");
        int j = 0;
        for (; j < startsizes[i] && j < hotsizes[i]; j += size) {
            lfs_file_read(&lfs, &file[0], buffer, size) => size;
            memcmp(buffer, "hair", size) => 0;
        }
        for (; j < hotsizes[i]; j += size) {
            lfs_file_read(&lfs, &file[0], buffer, size) => size;
            memcmp(buffer, "\0\0\0\0", size) => 0;
        }
        lfs_file_truncate(&lfs, &file[0], coldsizes[i]) => 0;
        lfs_file_size(&lfs, &file[0]) => coldsizes[i];
        lfs_file_close(&lfs, &file[0]) => 0;
    }
    lfs_unmount(&lfs) => 0;
 TEST
 tests/test.py << TEST
    static const lfs_off_t startsizes[] = {$STARTSIZES};
    static const lfs_off_t hotsizes[]   = {$HOTSIZES};
    static const lfs_off_t coldsizes[]  = {$COLDSIZES};
    lfs_mount(&lfs, &cfg) => 0;
    for (int i = 0; i < sizeof(startsizes)/sizeof(startsizes[0]); i++) {
        sprintf((char*)buffer, "hairyhead%d", i);
        lfs_file_open(&lfs, &file[0], (const char*)buffer, LFS_O_RDONLY) => 0;
        lfs_file_size(&lfs, &file[0]) => coldsizes[i];
        size = strlen("hair");
        int j = 0;
        for (; j < startsizes[i] && j < hotsizes[i] && j < coldsizes[i];
                j += size) {
            lfs_file_read(&lfs, &file[0], buffer, size) => size;
            memcmp(buffer, "hair", size) => 0;
        }
        for (; j < coldsizes[i]; j += size) {
            lfs_file_read(&lfs, &file[0], buffer, size) => size;
            memcmp(buffer, "\0\0\0\0", size) => 0;
        }
        lfs_file_close(&lfs, &file[0]) => 0;
    }
    lfs_unmount(&lfs) => 0;
 TEST
 }
 echo "--- Cold shrinking truncate ---"
 truncate_test \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE"
 echo "--- Cold expanding truncate ---"
 truncate_test \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE"
 echo "--- Warm shrinking truncate ---"
 truncate_test \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "           0,            0,            0,            0,            0"
 echo "--- Warm expanding truncate ---"
 truncate_test \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE"
 echo "--- Mid-file shrinking truncate ---"
 truncate_test \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "  $LARGESIZE,   $LARGESIZE,   $LARGESIZE,   $LARGESIZE,   $LARGESIZE" \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "           0,            0,            0,            0,            0"
 echo "--- Mid-file expanding truncate ---"
 truncate_test \
    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
    "           0,            0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE"
 echo "--- Results ---"
 tests/stats.py