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Added documentation over the underlying design

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Christopher Haster
2017-05-18 23:44:18 -05:00
parent 69294ac418
commit d2bf2bbc72
2 changed files with 1005 additions and 14 deletions
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README.md
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@@ -1,23 +1,33 @@
## The little filesystem
A little fail-safe filesystem designed for low ram/rom footprint.
A little fail-safe filesystem designed for embedded systems.
**Fail-safe** - The littlefs is designed to work consistently with random power
failures. During filesystem operations the storage on disk is always kept
in a valid state. The filesystem also has strong copy-on-write garuntees.
```
| | | .---._____
.-----. | |
--|o |---| littlefs |
--| |---| |
'-----' '----------'
| | |
```
**Fail-safe** - The littlefs is designed to work consistently with random
power failures. During filesystem operations the storage on disk is always
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.
**Handles bad blocks** - While the littlefs does not implement static wear
leveling, if the underlying block device reports write errors, the littlefs
uses a form of dynamic wear leveling to manage blocks that go bad during
the lifetime of the filesystem.
**Wear awareness** - While the littlefs does not implement static wear
leveling, the littlefs takes into account write errors reported by the
underlying block device and uses a limited form of dynamic wear leveling
to manage blocks that go bad during the lifetime of the filesystem.
**Constrained memory** - The littlefs is designed to work in bounded memory,
recursion is avoided, and dynamic memory is kept 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, these buffers can be
provided statically.
**Bounded ram/rom** - The littlefs is designed to work in a
limited amount of memory, recursion is avoided, and dynamic memory is kept
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
@@ -74,7 +84,7 @@ int main(void) {
// remember the storage is not updated until the file is closed successfully
lfs_file_close(&lfs, &file);
// release and resources we were using
// release any resources we were using
lfs_unmount(&lfs);
}
```
@@ -113,6 +123,14 @@ long as the machines involved share endianness and don't have really
strange padding requirements. If the question does come up, the littlefs
metadata should be stored on disk in little-endian format.
## Design
the littlefs was developed with the goal of learning 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.
More detail on the solutions and tradeoffs incorporated into this filesystem
can be found in [DESIGN.md](DESIGN.md).
## Testing
The littlefs comes with a test suite designed to run on a pc using the