Introduced the LFS_O_SNAPSHOT flag

LFS_O_SNAPSHOT brings back some of littlefs's idiosyncratic behavior
removed in the changes to open file syncing in a form that may be more
useful for users.

LFS_O_SNAPSHOT allows you to open a "snapshot" of a file. This is a cheap,
local copy of a file who's changes are not reflected on disk.

Internally, snapshot files use the same mechanism as pending writes. A
separate, copy-on-write CTZ skip-list is created, with read-only
references to the existing data blocks until a write occurs. The
difference is that snapshot files are not enrolled in the mlist, meaning
they won't get updates from open file syncs, and during close their
contents are simply discarded.

As an extra benefit, LFS_O_CREAT | LFS_O_SNAPSHOT is equivalent to
Linux's O_TMPFILE, making it easy to create temporary, unnamed files.

This may be useful for embedded development, where unnamed flash-backed
buffers may provide a slower, but larger, alternative to RAM-backed
buffers.

.travis.yml

@@ -208,6 +208,38 @@ jobs:
     script:
       - make test TFLAGS+="-k --valgrind"
 
+  # test compilation in read-only mode
+  - stage: test
+    env:
+      - NAME=littlefs-readonly
+      - CC="arm-linux-gnueabi-gcc --static -mthumb"
+      - CFLAGS="-Werror -DLFS_READONLY"
+    if: branch !~ -prefix$
+    install:
+      - *install-common
+      - sudo apt-get install
+            gcc-arm-linux-gnueabi
+            libc6-dev-armel-cross
+      - arm-linux-gnueabi-gcc --version
+    # report-size will compile littlefs and report the size
+    script: [*report-size]
+
+  # test compilation in thread-safe mode
+  - stage: test
+    env:
+      - NAME=littlefs-threadsafe
+      - CC="arm-linux-gnueabi-gcc --static -mthumb"
+      - CFLAGS="-Werror -DLFS_THREADSAFE"
+    if: branch !~ -prefix$
+    install:
+      - *install-common
+      - sudo apt-get install
+            gcc-arm-linux-gnueabi
+            libc6-dev-armel-cross
+      - arm-linux-gnueabi-gcc --version
+    # report-size will compile littlefs and report the size
+    script: [*report-size]
+
   # self-host with littlefs-fuse for fuzz test
   - stage: test
     env:

README.md

@@ -221,6 +221,11 @@ License Identifiers that are here available: http://spdx.org/licenses/
 - [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][littlefs-js-demo].
+  
+- [littlefs-python] - A Python wrapper for littlefs. The project allows you
+  to create images of the filesystem on your PC. Check if littlefs will fit
+  your needs, create images for a later download to the target memory or
+  inspect the content of a binary image of the target memory.
 
 - [mklfs] - A command line tool built by the [Lua RTOS] guys for making
   littlefs images from a host PC. Supports Windows, Mac OS, and Linux.
@@ -250,3 +255,4 @@ License Identifiers that are here available: http://spdx.org/licenses/
 [LittleFileSystem]: https://os.mbed.com/docs/mbed-os/v5.12/apis/littlefilesystem.html
 [SPIFFS]: https://github.com/pellepl/spiffs
 [Dhara]: https://github.com/dlbeer/dhara
+[littlefs-python]: https://pypi.org/project/littlefs-python/

bd/lfs_testbd.c

@@ -207,7 +207,7 @@ int lfs_testbd_prog(const struct lfs_config *cfg, lfs_block_t block,
         bd->power_cycles -= 1;
         if (bd->power_cycles == 0) {
             // sync to make sure we persist the last changes
-            assert(lfs_testbd_rawsync(cfg) == 0);
+            LFS_ASSERT(lfs_testbd_rawsync(cfg) == 0);
             // simulate power loss
             exit(33);
         }
@@ -254,7 +254,7 @@ int lfs_testbd_erase(const struct lfs_config *cfg, lfs_block_t block) {
         bd->power_cycles -= 1;
         if (bd->power_cycles == 0) {
             // sync to make sure we persist the last changes
-            assert(lfs_testbd_rawsync(cfg) == 0);
+            LFS_ASSERT(lfs_testbd_rawsync(cfg) == 0);
             // simulate power loss
             exit(33);
         }

lfs.h

@@ -9,6 +9,7 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include "lfs_util.h"
 
 #ifdef __cplusplus
 extern "C"
@@ -21,7 +22,7 @@ extern "C"
 // Software library version
 // Major (top-nibble), incremented on backwards incompatible changes
 // Minor (bottom-nibble), incremented on feature additions
-#define LFS_VERSION 0x00020002
+#define LFS_VERSION 0x00020003
 #define LFS_VERSION_MAJOR (0xffff & (LFS_VERSION >> 16))
 #define LFS_VERSION_MINOR (0xffff & (LFS_VERSION >>  0))
 
@@ -122,21 +123,30 @@ enum lfs_type {
 // File open flags
 enum lfs_open_flags {
     // open flags
-    LFS_O_RDONLY = 1,         // Open a file as read only
-    LFS_O_WRONLY = 2,         // Open a file as write only
-    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_EXCL   = 0x0200,    // Fail if a file already exists
-    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_RDONLY    = 1,        // Open a file as read only
+#ifndef LFS_READONLY
+    LFS_O_WRONLY    = 2,        // Open a file as write only
+    LFS_O_RDWR      = 3,        // Open a file as read and write
+#endif
+
+#ifndef LFS_READONLY
+    LFS_O_CREAT     = 0x0100,   // Create a file if it does not exist
+    LFS_O_EXCL      = 0x0200,   // Fail if a file already exists
+    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_SNAPSHOT  = 0x1000,   // Open a temporary snapshot, ignore changes
+#endif
 
     // internally used flags
-    LFS_F_DIRTY   = 0x010000, // File does not match storage
-    LFS_F_WRITING = 0x020000, // File has been written since last flush
-    LFS_F_READING = 0x040000, // 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
-    LFS_F_OPENED  = 0x200000, // File has been opened
+#ifndef LFS_READONLY
+    LFS_F_DIRTY     = 0x010000, // File does not match storage
+#endif
+    LFS_F_READING   = 0x020000, // File has been read since last flush
+#ifndef LFS_READONLY
+    LFS_F_WRITING   = 0x040000, // File has been written since last flush
+    LFS_F_ZOMBIE    = 0x080000, // An error occurred during write
+#endif
+    LFS_F_INLINE    = 0x100000, // Currently inlined in directory entry
 };
 
 // File seek flags
@@ -174,6 +184,16 @@ struct lfs_config {
     // are propogated to the user.
     int (*sync)(const struct lfs_config *c);
 
+#ifdef LFS_THREADSAFE
+    // Lock the underlying block device. Negative error codes
+    // are propogated to the user.
+    int (*lock)(const struct lfs_config *c);
+
+    // Unlock the underlying block device. Negative error codes
+    // are propogated to the user.
+    int (*unlock)(const struct lfs_config *c);
+#endif
+
     // Minimum size of a block read. All read operations will be a
     // multiple of this value.
     lfs_size_t read_size;
@@ -278,16 +298,15 @@ struct lfs_file_config {
     void *buffer;
 
     // Optional list of custom attributes related to the file. If the file
-    // is opened with read access, these attributes will be read from disk
-    // during the open call. If the file is opened with write access, the
-    // attributes will be written to disk every file sync or close. This
-    // write occurs atomically with update to the file's contents.
+    // is opened for reading, these attributes will be read from disk during
+    // open. If the file is open for writing, these attribute will be atomically
+    // written to disk when the file is written to disk. Note that these
+    // attributes are not written unless the file is modified.
     //
     // Custom attributes are uniquely identified by an 8-bit type and limited
-    // to LFS_ATTR_MAX bytes. When read, if the stored attribute is smaller
-    // than the buffer, it will be padded with zeros. If the stored attribute
-    // is larger, then it will be silently truncated. If the attribute is not
-    // found, it will be created implicitly.
+    // to LFS_ATTR_MAX bytes. If the stored attribute is larger than the
+    // provided buffer, it will be silently truncated. If no attribute is
+    // found, and the file is open for writing, it will be created implicitly.
     struct lfs_attr *attrs;
 
     // Number of custom attributes in the list
@@ -399,6 +418,7 @@ typedef struct lfs {
 
 /// Filesystem functions ///
 
+#ifndef LFS_READONLY
 // Format a block device with the littlefs
 //
 // Requires a littlefs object and config struct. This clobbers the littlefs
@@ -407,6 +427,7 @@ typedef struct lfs {
 //
 // Returns a negative error code on failure.
 int lfs_format(lfs_t *lfs, const struct lfs_config *config);
+#endif
 
 // Mounts a littlefs
 //
@@ -426,12 +447,15 @@ int lfs_unmount(lfs_t *lfs);
 
 /// General operations ///
 
+#ifndef LFS_READONLY
 // Removes a file or directory
 //
 // If removing a directory, the directory must be empty.
 // Returns a negative error code on failure.
 int lfs_remove(lfs_t *lfs, const char *path);
+#endif
 
+#ifndef LFS_READONLY
 // Rename or move a file or directory
 //
 // If the destination exists, it must match the source in type.
@@ -439,6 +463,7 @@ int lfs_remove(lfs_t *lfs, const char *path);
 //
 // Returns a negative error code on failure.
 int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath);
+#endif
 
 // Find info about a file or directory
 //
@@ -449,10 +474,9 @@ int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info);
 // Get a custom attribute
 //
 // Custom attributes are uniquely identified by an 8-bit type and limited
-// to LFS_ATTR_MAX bytes. When read, if the stored attribute is smaller than
-// the buffer, it will be padded with zeros. If the stored attribute is larger,
-// then it will be silently truncated. If no attribute is found, the error
-// LFS_ERR_NOATTR is returned and the buffer is filled with zeros.
+// to LFS_ATTR_MAX bytes. If the stored attribute is larger than the
+// provided buffer, it will be silently truncated. If no attribute is found,
+// the error LFS_ERR_NOATTR is returned and the buffer is filled with zeros.
 //
 // Returns the size of the attribute, or a negative error code on failure.
 // Note, the returned size is the size of the attribute on disk, irrespective
@@ -461,6 +485,7 @@ int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info);
 lfs_ssize_t lfs_getattr(lfs_t *lfs, const char *path,
         uint8_t type, void *buffer, lfs_size_t size);
 
+#ifndef LFS_READONLY
 // Set custom attributes
 //
 // Custom attributes are uniquely identified by an 8-bit type and limited
@@ -470,13 +495,16 @@ lfs_ssize_t lfs_getattr(lfs_t *lfs, const char *path,
 // Returns a negative error code on failure.
 int lfs_setattr(lfs_t *lfs, const char *path,
         uint8_t type, const void *buffer, lfs_size_t size);
+#endif
 
+#ifndef LFS_READONLY
 // Removes a custom attribute
 //
 // If an attribute is not found, nothing happens.
 //
 // Returns a negative error code on failure.
 int lfs_removeattr(lfs_t *lfs, const char *path, uint8_t type);
+#endif
 
 
 /// File operations ///
@@ -525,6 +553,7 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file);
 lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
         void *buffer, lfs_size_t size);
 
+#ifndef LFS_READONLY
 // Write data to file
 //
 // Takes a buffer and size indicating the data to write. The file will not
@@ -533,6 +562,7 @@ lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
 // Returns the number of bytes written, or a negative error code on failure.
 lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
         const void *buffer, lfs_size_t size);
+#endif
 
 // Change the position of the file
 //
@@ -541,10 +571,12 @@ 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);
 
+#ifndef LFS_READONLY
 // 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);
+#endif
 
 // Return the position of the file
 //
@@ -567,10 +599,12 @@ lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file);
 
 /// Directory operations ///
 
+#ifndef LFS_READONLY
 // Create a directory
 //
 // Returns a negative error code on failure.
 int lfs_mkdir(lfs_t *lfs, const char *path);
+#endif
 
 // Open a directory
 //
@@ -632,6 +666,7 @@ lfs_ssize_t lfs_fs_size(lfs_t *lfs);
 // Returns a negative error code on failure.
 int lfs_fs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data);
 
+#ifndef LFS_READONLY
 #ifdef LFS_MIGRATE
 // Attempts to migrate a previous version of littlefs
 //
@@ -646,6 +681,7 @@ int lfs_fs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data);
 // Returns a negative error code on failure.
 int lfs_migrate(lfs_t *lfs, const struct lfs_config *cfg);
 #endif
+#endif
 
 
 #ifdef __cplusplus

scripts/readtree.py

@@ -106,7 +106,7 @@ def main(args):
             struct.unpack('<HH', superblock[1].data[0:4].ljust(4, b'\xff'))))
     print("%-47s%s" % ("littlefs v%s.%s" % version,
         "data (truncated, if it fits)"
-        if not any([args.no_truncate, args.tags, args.log, args.all]) else ""))
+        if not any([args.no_truncate, args.log, args.all]) else ""))
 
     # print gstate
     print("gstate 0x%s" % ''.join('%02x' % c for c in gstate))

tests/test_attrs.toml

@@ -16,41 +16,39 @@ code = '''
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
-    memcmp(buffer+4,  "bbbbbb", 6) => 0;
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
+    assert(memcmp(buffer+4,  "bbbbbb", 6) == 0);
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "hello", 'B', "", 0) => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 0;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",        5) => 0;
+    assert(memcmp(buffer,    "aaaa",         4) == 0);
+    assert(memcmp(buffer+10, "ccccc",        5) == 0);
 
     lfs_removeattr(&lfs, "hello", 'B') => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => LFS_ERR_NOATTR;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",        5) => 0;
+    assert(memcmp(buffer,    "aaaa",         4) == 0);
+    assert(memcmp(buffer+10, "ccccc",        5) == 0);
 
     lfs_setattr(&lfs, "hello", 'B', "dddddd", 6) => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
-    memcmp(buffer+4,  "dddddd", 6) => 0;
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
+    assert(memcmp(buffer+4,  "dddddd", 6) == 0);
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "hello", 'B', "eee", 3) => 0;
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  6) => 3;
     lfs_getattr(&lfs, "hello", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
-    memcmp(buffer+4,  "eee\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",     5) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
+    assert(memcmp(buffer+4,  "eee",   3) == 0);
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     lfs_setattr(&lfs, "hello", 'A', buffer, LFS_ATTR_MAX+1) => LFS_ERR_NOSPC;
     lfs_setattr(&lfs, "hello", 'B', "fffffffff", 9) => 0;
@@ -65,13 +63,13 @@ code = '''
     lfs_getattr(&lfs, "hello", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "hello", 'B', buffer+4,  9) => 9;
     lfs_getattr(&lfs, "hello", 'C', buffer+13, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
-    memcmp(buffer+4,  "fffffffff", 9) => 0;
-    memcmp(buffer+13, "ccccc",     5) => 0;
+    assert(memcmp(buffer,    "aaaa",      4) == 0);
+    assert(memcmp(buffer+4,  "fffffffff", 9) == 0);
+    assert(memcmp(buffer+13, "ccccc",     5) == 0);
 
     lfs_file_open(&lfs, &file, "hello/hello", LFS_O_RDONLY) => 0;
     lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => strlen("hello");
-    memcmp(buffer, "hello", strlen("hello")) => 0;
+    assert(memcmp(buffer, "hello", strlen("hello")) == 0);
     lfs_file_close(&lfs, &file);
     lfs_unmount(&lfs) => 0;
 '''
@@ -94,41 +92,39 @@ code = '''
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
-    memcmp(buffer+4,  "bbbbbb", 6) => 0;
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
+    assert(memcmp(buffer+4,  "bbbbbb", 6) == 0);
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "/", 'B', "", 0) => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 0;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",        5) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     lfs_removeattr(&lfs, "/", 'B') => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => LFS_ERR_NOATTR;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",         4) => 0;
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",        5) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     lfs_setattr(&lfs, "/", 'B', "dddddd", 6) => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 6;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",   4) => 0;
-    memcmp(buffer+4,  "dddddd", 6) => 0;
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
+    assert(memcmp(buffer+4,  "dddddd", 6) == 0);
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     lfs_setattr(&lfs, "/", 'B', "eee", 3) => 0;
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  6) => 3;
     lfs_getattr(&lfs, "/", 'C', buffer+10, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
-    memcmp(buffer+4,  "eee\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",     5) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
+    assert(memcmp(buffer+4,  "eee",   3) == 0);
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     lfs_setattr(&lfs, "/", 'A', buffer, LFS_ATTR_MAX+1) => LFS_ERR_NOSPC;
     lfs_setattr(&lfs, "/", 'B', "fffffffff", 9) => 0;
@@ -142,13 +138,13 @@ code = '''
     lfs_getattr(&lfs, "/", 'A', buffer,    4) => 4;
     lfs_getattr(&lfs, "/", 'B', buffer+4,  9) => 9;
     lfs_getattr(&lfs, "/", 'C', buffer+13, 5) => 5;
-    memcmp(buffer,    "aaaa",      4) => 0;
-    memcmp(buffer+4,  "fffffffff", 9) => 0;
-    memcmp(buffer+13, "ccccc",     5) => 0;
+    assert(memcmp(buffer,    "aaaa",      4) == 0);
+    assert(memcmp(buffer+4,  "fffffffff", 9) == 0);
+    assert(memcmp(buffer+13, "ccccc",     5) == 0);
 
     lfs_file_open(&lfs, &file, "hello/hello", LFS_O_RDONLY) => 0;
     lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => strlen("hello");
-    memcmp(buffer, "hello", strlen("hello")) => 0;
+    assert(memcmp(buffer, "hello", strlen("hello")) == 0);
     lfs_file_close(&lfs, &file);
     lfs_unmount(&lfs) => 0;
 '''
@@ -176,52 +172,55 @@ code = '''
     memcpy(buffer,    "aaaa",   4);
     memcpy(buffer+4,  "bbbbbb", 6);
     memcpy(buffer+10, "ccccc",  5);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",   4) => 0;
-    memcmp(buffer+4,  "bbbbbb", 6) => 0;
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
+    assert(memcmp(buffer+4,  "bbbbbb", 6) == 0);
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     attrs1[1].size = 0;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1) => 0;
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",         4) => 0;
-    memcmp(buffer+4,  "\0\0\0\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",        5) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1) => 0;
     memcpy(buffer+4,  "dddddd", 6);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",   4) => 0;
-    memcmp(buffer+4,  "dddddd", 6) => 0;
-    memcmp(buffer+10, "ccccc",  5) => 0;
+    assert(memcmp(buffer,    "aaaa",   4) == 0);
+    assert(memcmp(buffer+4,  "dddddd", 6) == 0);
+    assert(memcmp(buffer+10, "ccccc",  5) == 0);
 
     attrs1[1].size = 3;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1) => 0;
     memcpy(buffer+4,  "eee", 3);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     memset(buffer, 0, 15);
     attrs1[1].size = 6;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",      4) => 0;
-    memcmp(buffer+4,  "eee\0\0\0", 6) => 0;
-    memcmp(buffer+10, "ccccc",     5) => 0;
+    assert(memcmp(buffer,    "aaaa",  4) == 0);
+    assert(memcmp(buffer+4,  "eee",   3) == 0);
+    assert(memcmp(buffer+10, "ccccc", 5) == 0);
 
     attrs1[0].size = LFS_ATTR_MAX+1;
-    lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_WRONLY, &cfg1)
-        => LFS_ERR_NOSPC;
+    lfs_file_opencfg(&lfs, &file, "hello/hello2",
+            LFS_O_WRONLY | LFS_O_CREAT, &cfg1) => LFS_ERR_NOSPC;
 
     struct lfs_attr attrs2[] = {
         {'A', buffer,    4},
@@ -231,6 +230,7 @@ code = '''
     struct lfs_file_config cfg2 = {.attrs=attrs2, .attr_count=3};
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDWR, &cfg2) => 0;
     memcpy(buffer+4,  "fffffffff", 9);
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_close(&lfs, &file) => 0;
     attrs1[0].size = 4;
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg1) => 0;
@@ -249,13 +249,13 @@ code = '''
 
     lfs_file_opencfg(&lfs, &file, "hello/hello", LFS_O_RDONLY, &cfg3) => 0;
     lfs_file_close(&lfs, &file) => 0;
-    memcmp(buffer,    "aaaa",      4) => 0;
-    memcmp(buffer+4,  "fffffffff", 9) => 0;
-    memcmp(buffer+13, "ccccc",     5) => 0;
+    assert(memcmp(buffer,    "aaaa",      4) == 0);
+    assert(memcmp(buffer+4,  "fffffffff", 9) == 0);
+    assert(memcmp(buffer+13, "ccccc",     5) == 0);
 
     lfs_file_open(&lfs, &file, "hello/hello", LFS_O_RDONLY) => 0;
     lfs_file_read(&lfs, &file, buffer, sizeof(buffer)) => strlen("hello");
-    memcmp(buffer, "hello", strlen("hello")) => 0;
+    assert(memcmp(buffer, "hillo", strlen("hello")) == 0);
     lfs_file_close(&lfs, &file);
     lfs_unmount(&lfs) => 0;
 '''
@@ -287,17 +287,16 @@ code = '''
     lfs_getattr(&lfs, "hello/hello", 'B', buffer,    9) => 9;
     lfs_getattr(&lfs, "hello/hello", 'C', buffer+9,  9) => 5;
     lfs_getattr(&lfs, "hello/hello", 'D', buffer+18, 9) => LFS_ERR_NOATTR;
-    memcmp(buffer,    "fffffffff",          9) => 0;
-    memcmp(buffer+9,  "ccccc\0\0\0\0",      9) => 0;
-    memcmp(buffer+18, "\0\0\0\0\0\0\0\0\0", 9) => 0;
+    assert(memcmp(buffer,    "fffffffff", 9) == 0);
+    assert(memcmp(buffer+9,  "ccccc",     5) == 0);
 
+    lfs_file_write(&lfs, &file, "hi", 2) => 2;
     lfs_file_sync(&lfs, &file) => 0;
     lfs_getattr(&lfs, "hello/hello", 'B', buffer,    9) => 4;
     lfs_getattr(&lfs, "hello/hello", 'C', buffer+9,  9) => 0;
     lfs_getattr(&lfs, "hello/hello", 'D', buffer+18, 9) => 4;
-    memcmp(buffer,    "gggg\0\0\0\0\0",     9) => 0;
-    memcmp(buffer+9,  "\0\0\0\0\0\0\0\0\0", 9) => 0;
-    memcmp(buffer+18, "hhhh\0\0\0\0\0",     9) => 0;
+    assert(memcmp(buffer,    "gggg", 4) == 0);
+    assert(memcmp(buffer+18, "hhhh", 4) == 0);
 
     lfs_file_close(&lfs, &file) => 0;
     lfs_unmount(&lfs) => 0;

tests/test_interspersed.toml

@@ -1,7 +1,7 @@
 
 [[case]] # interspersed file test
 define.SIZE = [10, 100]
-define.FILES = [4, 10, 26] 
+define.FILES = [4, 10, 26]
 code = '''
     lfs_file_t files[FILES];
     const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
@@ -55,7 +55,7 @@ code = '''
     for (int j = 0; j < FILES; j++) {
         lfs_file_close(&lfs, &files[j]);
     }
-    
+
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -108,7 +108,7 @@ code = '''
         assert(buffer[0] == '~');
     }
     lfs_file_close(&lfs, &file);
-    
+
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -168,13 +168,13 @@ code = '''
     }
     lfs_file_close(&lfs, &files[0]);
     lfs_file_close(&lfs, &files[1]);
-    
+
     lfs_unmount(&lfs) => 0;
 '''
 
 [[case]] # reentrant interspersed file test
 define.SIZE = [10, 100]
-define.FILES = [4, 10, 26] 
+define.FILES = [4, 10, 26]
 reentrant = true
 code = '''
     lfs_file_t files[FILES];
@@ -239,6 +239,698 @@ code = '''
     for (int j = 0; j < FILES; j++) {
         lfs_file_close(&lfs, &files[j]);
     }
-    
+
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # open same file reading from separate file handles
+define.READERS = 3
+define.SIZE = [10, 100, 1000, 10000]
+define.RDMODE = ['LFS_O_RDONLY', 'LFS_O_RDWR']
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_open(&lfs, &file, "shared", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open all files
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t readers[READERS];
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_open(&lfs, &readers[i], "shared", RDMODE) => 0;
+    }
+
+    // perform operations while all readers are open
+    for (int i = 0; i < READERS; i++) {
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == alphas[j % 26]);
+        }
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_close(&lfs, &readers[i]) => 0;
+    }
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # open same file reading and writing from separate file handles
+define.READERS = 3
+define.SIZE = [10, 100, 1000, 10000]
+define.RDMODE = ['LFS_O_RDONLY', 'LFS_O_RDWR']
+define.WRMODE = ['LFS_O_WRONLY', 'LFS_O_RDWR']
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_open(&lfs, &file, "shared", LFS_O_CREAT | LFS_O_WRONLY) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open all files
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t writer;
+    lfs_file_t readers[READERS];
+    lfs_file_open(&lfs, &writer, "shared", WRMODE) => 0;
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_open(&lfs, &readers[i], "shared", RDMODE) => 0;
+    }
+
+    // perform operations while all readers are open
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &nums[j % 10], 1) => 1;
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        for (int j = 0; j < SIZE/2; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == alphas[j % 26]);
+        }
+    }
+
+    // sync, now write should reflect in all open files
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    for (int i = 0; i < READERS; i++) {
+        for (int j = SIZE/2; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    // double check our writer reflects its own changes
+    if (WRMODE == LFS_O_RDWR) {
+        lfs_file_rewind(&lfs, &writer) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &writer, buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_close(&lfs, &readers[i]) => 0;
+    }
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # check that attributes are updated in open files
+define.READERS = 3
+define.SIZE = 10
+define.RDMODE = ['LFS_O_RDONLY', 'LFS_O_RDWR']
+define.WRMODE = ['LFS_O_WRONLY', 'LFS_O_RDWR']
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 3,
+        .attrs = (struct lfs_attr[]){
+            {'A', "a",   1},
+            {'B', "bb",  2},
+            {'C', "ccc", 3},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "shared",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open all files
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t writer;
+    const struct lfs_file_config writercfg = {
+        .attr_count = 3,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[1]){0}, 1},
+            {'B', &(uint8_t[2]){0}, 2},
+            {'C', &(uint8_t[3]){0}, 3}}};
+    lfs_file_t readers[READERS];
+    const struct lfs_file_config readercfgs[READERS] = {
+        {   .attr_count = 3,
+            .attrs = (struct lfs_attr[]){
+                {'A', &(uint8_t[1]){0}, 1},
+                {'B', &(uint8_t[2]){0}, 2},
+                {'C', &(uint8_t[3]){0}, 3}}},
+        {   .attr_count = 3,
+            .attrs = (struct lfs_attr[]){
+                {'A', &(uint8_t[1]){0}, 1},
+                {'B', &(uint8_t[2]){0}, 2},
+                {'C', &(uint8_t[3]){0}, 3}}},
+        {   .attr_count = 3,
+            .attrs = (struct lfs_attr[]){
+                {'A', &(uint8_t[1]){0}, 1},
+                {'B', &(uint8_t[2]){0}, 2},
+                {'C', &(uint8_t[3]){0}, 3}}}};
+    lfs_file_opencfg(&lfs, &writer, "shared",
+            WRMODE, &writercfg) => 0;
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_opencfg(&lfs, &readers[i], "shared",
+                RDMODE, &readercfgs[i]) => 0;
+    }
+
+    // perform operations while all readers are open
+    writercfg.attrs[0].size = 1;
+    memcpy(writercfg.attrs[0].buffer, "0", 1);
+    writercfg.attrs[1].size = 2;
+    memcpy(writercfg.attrs[1].buffer, "11", 2);
+    writercfg.attrs[2].size = 3;
+    memcpy(writercfg.attrs[2].buffer, "222", 3);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &nums[j % 10], 1) => 1;
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        assert(readercfgs[i].attrs[0].size == 1);
+        assert(memcmp(readercfgs[i].attrs[0].buffer, "a", 1) == 0);
+        assert(readercfgs[i].attrs[1].size == 2);
+        assert(memcmp(readercfgs[i].attrs[1].buffer, "bb", 2) == 0);
+        assert(readercfgs[i].attrs[2].size == 3);
+        assert(memcmp(readercfgs[i].attrs[2].buffer, "ccc", 3) == 0);
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == alphas[j % 26]);
+        }
+    }
+
+    // sync, now write should reflect in all open files
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    for (int i = 0; i < READERS; i++) {
+        assert(readercfgs[i].attrs[0].size == 1);
+        assert(memcmp(readercfgs[i].attrs[0].buffer, "0", 1) == 0);
+        assert(readercfgs[i].attrs[1].size == 2);
+        assert(memcmp(readercfgs[i].attrs[1].buffer, "11", 2) == 0);
+        assert(readercfgs[i].attrs[2].size == 3);
+        assert(memcmp(readercfgs[i].attrs[2].buffer, "222", 3) == 0);
+        lfs_file_rewind(&lfs, &readers[i]) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    // double check our writer reflects its own changes
+    if (WRMODE == LFS_O_RDWR) {
+        assert(writercfg.attrs[0].size == 1);
+        assert(memcmp(writercfg.attrs[0].buffer, "0", 1) == 0);
+        assert(writercfg.attrs[1].size == 2);
+        assert(memcmp(writercfg.attrs[1].buffer, "11", 2) == 0);
+        assert(writercfg.attrs[2].size == 3);
+        assert(memcmp(writercfg.attrs[2].buffer, "222", 3) == 0);
+        lfs_file_rewind(&lfs, &writer) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &writer, buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    // now try explicit lfs_setattr calls, this should still update open files
+    lfs_setattr(&lfs, "shared", 'A', "A",   1) => 0;
+    lfs_setattr(&lfs, "shared", 'B', "BB",  2) => 0;
+    lfs_setattr(&lfs, "shared", 'C', "CCC", 3) => 0;
+
+    for (int i = 0; i < READERS; i++) {
+        assert(readercfgs[i].attrs[0].size == 1);
+        assert(memcmp(readercfgs[i].attrs[0].buffer, "A", 1) == 0);
+        assert(readercfgs[i].attrs[1].size == 2);
+        assert(memcmp(readercfgs[i].attrs[1].buffer, "BB", 2) == 0);
+        assert(readercfgs[i].attrs[2].size == 3);
+        assert(memcmp(readercfgs[i].attrs[2].buffer, "CCC", 3) == 0);
+        lfs_file_rewind(&lfs, &readers[i]) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &readers[i], buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    }
+
+    if (WRMODE == LFS_O_RDWR) {
+        assert(writercfg.attrs[0].size == 1);
+        assert(memcmp(writercfg.attrs[0].buffer, "A", 1) == 0);
+        assert(writercfg.attrs[1].size == 2);
+        assert(memcmp(writercfg.attrs[1].buffer, "BB", 2) == 0);
+        assert(writercfg.attrs[2].size == 3);
+        assert(memcmp(writercfg.attrs[2].buffer, "CCC", 3) == 0);
+        lfs_file_rewind(&lfs, &writer) => 0;
+        for (int j = 0; j < SIZE; j++) {
+            lfs_file_read(&lfs, &writer, buffer, 1) => 1;
+            assert(buffer[0] == nums[j % 10]);
+        }
+    } else if (WRMODE == LFS_O_WRONLY) {
+        // this should NOT update wronly attributes, these may be
+        // stored in read-only memory
+        assert(writercfg.attrs[0].size == 1);
+        assert(memcmp(writercfg.attrs[0].buffer, "0", 1) == 0);
+        assert(writercfg.attrs[1].size == 2);
+        assert(memcmp(writercfg.attrs[1].buffer, "11", 2) == 0);
+        assert(writercfg.attrs[2].size == 3);
+        assert(memcmp(writercfg.attrs[2].buffer, "222", 3) == 0);
+    }
+
+    for (int i = 0; i < READERS; i++) {
+        lfs_file_close(&lfs, &readers[i]) => 0;
+    }
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # simple snapshot for reading
+define.SIZE = [10, 100, 1000, 10000]
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', "abcd", 4},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open reader/writer/snapshot
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t reader;
+    const struct lfs_file_config readercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t writer;
+    const struct lfs_file_config writercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t snapshot;
+    const struct lfs_file_config snapshotcfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    lfs_file_opencfg(&lfs, &writer, "open_me",
+            LFS_O_WRONLY, &writercfg) => 0;
+    lfs_file_opencfg(&lfs, &snapshot, "open_me",
+            LFS_O_RDONLY | LFS_O_SNAPSHOT, &snapshotcfg) => 0;
+
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // write file
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &nums[j % 10], 1) => 1;
+    }
+    memcpy(writercfg.attrs[0].buffer, "0123", 4);
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    // reader should change
+    assert(memcmp(readercfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    // snapshot should remain unchanged
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_close(&lfs, &writer) => 0;
+    lfs_file_close(&lfs, &snapshot) => 0;
+
+    // disk should change
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # simple snapshot for writing
+define.SIZE = [10, 100, 1000, 10000]
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', "abcd", 4},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open reader/snapshot
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t reader;
+    const struct lfs_file_config readercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t snapshot;
+    const struct lfs_file_config snapshotcfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    lfs_file_opencfg(&lfs, &snapshot, "open_me",
+            LFS_O_RDWR | LFS_O_SNAPSHOT, &snapshotcfg) => 0;
+
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // modify snapshot
+    lfs_file_rewind(&lfs, &snapshot) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &snapshot, &nums[j % 10], 1) => 1;
+    }
+    memcpy(snapshotcfg.attrs[0].buffer, "0123", 4);
+
+    lfs_file_rewind(&lfs, &snapshot) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_sync(&lfs, &snapshot) => 0;
+
+    // reader should not change
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // snapshot should changed
+    assert(memcmp(snapshotcfg.attrs[0].buffer, "0123", 4) == 0);
+    lfs_file_rewind(&lfs, &snapshot) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &snapshot, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_close(&lfs, &snapshot) => 0;
+
+    // disk should not change
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # temporary files
+define.SIZE = [10, 100, 1000, 10000]
+define.TMP_PATH = 'range(4)'
+code = '''
+    const char alphas[] = "abcdefghijklmnopqrstuvwxyz";
+    const char nums[] = "0123456789";
+    const char caps[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    const struct lfs_file_config filecfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', "abcd", 4},
+        },
+    };
+    lfs_file_opencfg(&lfs, &file, "open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_file_opencfg(&lfs, &file, "dont_open_me",
+            LFS_O_CREAT | LFS_O_WRONLY, &filecfg) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &file, &alphas[j % 26], 1) => 1;
+    }
+    lfs_file_close(&lfs, &file) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    // open reader/writer/temp
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_t reader;
+    const struct lfs_file_config readercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t writer;
+    const struct lfs_file_config writercfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_t tmp;
+    const struct lfs_file_config tmpcfg = {
+        .attr_count = 1,
+        .attrs = (struct lfs_attr[]){
+            {'A', &(uint8_t[4]){0}, 4}
+        },
+    };
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    lfs_file_opencfg(&lfs, &writer, "open_me",
+            LFS_O_WRONLY, &writercfg) => 0;
+    const char *tmp_paths[] = {NULL, "/", "/tmp", "/open_me.tmp"};
+    lfs_file_opencfg(&lfs, &tmp, tmp_paths[TMP_PATH],
+            LFS_O_RDWR | LFS_O_CREAT | LFS_O_SNAPSHOT, &tmpcfg) => 0;
+
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE/3; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    assert(memcmp(tmpcfg.attrs[0].buffer, "\0\0\0\0", 4) == 0);
+    assert(lfs_file_size(&lfs, &tmp) == 0);
+
+    // write to tmp
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &tmp, &nums[j % 10], 1) => 1;
+    }
+    memcpy(tmpcfg.attrs[0].buffer, "0123", 4);
+
+    lfs_file_rewind(&lfs, &tmp) => 0;
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &tmp, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_sync(&lfs, &tmp) => 0;
+
+    // reader should not change
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = SIZE/3; j < 2*SIZE/3; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+
+    // tmp should change
+    assert(memcmp(tmpcfg.attrs[0].buffer, "0123", 4) == 0);
+    lfs_file_rewind(&lfs, &tmp) => 0;
+    for (int j = 0; j < SIZE/2; j++) {
+        lfs_file_read(&lfs, &tmp, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    // write to file
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_write(&lfs, &writer, &caps[j % 26], 1) => 1;
+    }
+    memcpy(writercfg.attrs[0].buffer, "ABCD", 4);
+    lfs_file_sync(&lfs, &writer) => 0;
+
+    // reader should change
+    assert(memcmp(readercfg.attrs[0].buffer, "ABCD", 4) == 0);
+    for (int j = 2*SIZE/3; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == caps[j % 26]);
+    }
+
+    // tmp should not change
+    assert(memcmp(tmpcfg.attrs[0].buffer, "0123", 4) == 0);
+    for (int j = SIZE/2; j < SIZE; j++) {
+        lfs_file_read(&lfs, &tmp, buffer, 1) => 1;
+        assert(buffer[0] == nums[j % 10]);
+    }
+
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_close(&lfs, &writer) => 0;
+    lfs_file_close(&lfs, &tmp) => 0;
+
+    // tmp should not appear on disk
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "dont_open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "ABCD", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == caps[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_opencfg(&lfs, &reader, "dont_open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_dir_open(&lfs, &dir, "/") => 0;
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, ".") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_DIR);
+    assert(strcmp(info.name, "..") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "dont_open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 1;
+    assert(info.type == LFS_TYPE_REG);
+    assert(strcmp(info.name, "open_me") == 0);
+    lfs_dir_read(&lfs, &dir, &info) => 0;
+    lfs_dir_close(&lfs, &dir) => 0;
+    lfs_file_opencfg(&lfs, &reader, "open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "ABCD", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == caps[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_file_opencfg(&lfs, &reader, "dont_open_me",
+            LFS_O_RDONLY, &readercfg) => 0;
+    assert(memcmp(readercfg.attrs[0].buffer, "abcd", 4) == 0);
+    for (int j = 0; j < SIZE; j++) {
+        lfs_file_read(&lfs, &reader, buffer, 1) => 1;
+        assert(buffer[0] == alphas[j % 26]);
+    }
+    lfs_file_close(&lfs, &reader) => 0;
+    lfs_unmount(&lfs) => 0;
+'''
+
+[[case]] # test snapshot open errors
+code = '''
+    lfs_format(&lfs, &cfg) => 0;
+    lfs_mount(&lfs, &cfg) => 0;
+    lfs_file_open(&lfs, &file, NULL,
+            LFS_O_RDWR | LFS_O_SNAPSHOT) => LFS_ERR_ISDIR;
+    lfs_file_open(&lfs, &file, "/",
+            LFS_O_RDWR | LFS_O_SNAPSHOT) => LFS_ERR_ISDIR;
+    lfs_file_open(&lfs, &file, "/tmp",
+            LFS_O_RDWR | LFS_O_SNAPSHOT) => LFS_ERR_NOENT;
+    lfs_file_open(&lfs, &file, "/tmp/",
+            LFS_O_RDWR | LFS_O_CREAT | LFS_O_SNAPSHOT) => LFS_ERR_NOENT;
+    lfs_file_open(&lfs, &file, "/tmp/tmp",
+            LFS_O_RDWR | LFS_O_CREAT | LFS_O_SNAPSHOT) => LFS_ERR_NOENT;
     lfs_unmount(&lfs) => 0;
 '''

tests/test_paths.toml

@@ -95,9 +95,9 @@ code = '''
 
     lfs_mkdir(&lfs, "coffee/../milk") => 0;
     lfs_stat(&lfs, "coffee/../milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_stat(&lfs, "milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -129,9 +129,9 @@ code = '''
     lfs_mount(&lfs, &cfg) => 0;
     lfs_mkdir(&lfs, ".milk") => 0;
     lfs_stat(&lfs, ".milk", &info) => 0;
-    strcmp(info.name, ".milk") => 0;
+    assert(strcmp(info.name, ".milk") == 0);
     lfs_stat(&lfs, "tea/.././.milk", &info) => 0;
-    strcmp(info.name, ".milk") => 0;
+    assert(strcmp(info.name, ".milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''
 
@@ -149,13 +149,13 @@ code = '''
     lfs_mkdir(&lfs, "coffee/coldcoffee") => 0;
 
     lfs_stat(&lfs, "coffee/../../../../../../tea/hottea", &info) => 0;
-    strcmp(info.name, "hottea") => 0;
+    assert(strcmp(info.name, "hottea") == 0);
 
     lfs_mkdir(&lfs, "coffee/../../../../../../milk") => 0;
     lfs_stat(&lfs, "coffee/../../../../../../milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_stat(&lfs, "milk", &info) => 0;
-    strcmp(info.name, "milk") => 0;
+    assert(strcmp(info.name, "milk") == 0);
     lfs_unmount(&lfs) => 0;
 '''