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Shoehorned in hacky implementation of inline files

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Proof-of-concept implementation of inline files that stores the file's
content directly in its parent's directory pair.

Inline files are indicated by a different type stored in an entry's
struct field, and take advantage of resizable entries. Where a normal
file's entry would normally hold the reference to the CTZ skip-list, an
inline file's entry contains the contents of the actual file.

Unfortunately, storing the inline file on disk is the easy part. We also
need to manage inline files in the internals of littlefs and provide the
same operations that we do on normal files, all while reusing as much
code as possible to avoid a significant increase in code cost.

There is a relatively simple, though maybe a bit hacky, solution here. If a
file fits entirely in a cache line, the file logic never actually has to go to
disk. This means we can just give the file a "pretend" block (hopefully
one that would assert if ever written to), and carry out file operations
as normal, as long as we catch the file before it exceeds the cache line
and write out the file to an actual disk.
This commit is contained in:
Christopher Haster
2018-03-17 10:28:14 -05:00
parent fb23044872
commit 836e23895a
3 changed files with 133 additions and 60 deletions
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28
lfs.h
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@@ -55,6 +55,10 @@ typedef uint32_t lfs_block_t;
#define LFS_NAME_MAX 255
#endif
#ifndef LFS_INLINE_MAX
#define LFS_INLINE_MAX 255
#endif
// Possible error codes, these are negative to allow
// valid positive return values
enum lfs_error {
@@ -82,25 +86,27 @@ enum lfs_type {
// 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_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
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
// internally used flags
LFS_F_DIRTY = 0x10000, // File does not match storage
LFS_F_WRITING = 0x20000, // File has been written since last flush
LFS_F_READING = 0x40000, // File has been read since last flush
LFS_F_ERRED = 0x80000, // An error occured during write
LFS_F_DIRTY = 0x10000, // File does not match storage
LFS_F_WRITING = 0x20000, // File has been written since last flush
LFS_F_READING = 0x40000, // File has been read since last flush
LFS_F_ERRED = 0x80000, // An error occured during write
LFS_F_INLINE = 0x100000, // Currently inlined in directory entry
};
// File seek flags