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Cleaned up tag encoding, now with clear chunk field

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Before, the tag format's type field was limited to 9-bits. This sounds
like a lot, but this field needed to encode up to 256 user-specified
types. This limited the flexibility of the encoded types. As time went
on, more bits in the type field were repurposed for various things,
leaving a rather fragile type field.

Here we make the jump to full 11-bit type fields. This comes at the cost
of a smaller length field, however the use of the length field was
always going to come with a RAM limitation. Rather than putting pressure
on RAM for inline files, the new type field lets us encode a chunk
number, splitting up inline files into multiple updatable units. This
actually pushes the theoretical inline max from 8KiB to 256KiB! (Note
that we only allow a single 1KiB chunk for now, chunky inline files
is just a theoretical future improvement).

Here is the new 32-bit tag format, note that there are multiple levels
of types which break down into more info:

[----            32             ----]
[1|--  11   --|--  10  --|--  10  --]
 ^.     ^     .     ^          ^- entry length
 |.     |     .     \------------ file id chunk info
 |.     \-----.------------------ type info (type3)
 \.-----------.------------------ valid bit
  [-3-|-- 8 --]
    ^     ^- chunk info
    \------- type info (type1)

Additionally, I've split the CREATE tag into separate SPLICE and NAME
tags. This simplified the new compact logic a bit. For now, littlefs
still follows the rule that a NAME tag precedes any other tags related
to a file, but this can change in the future.
This commit is contained in:
Christopher Haster
2018-12-29 07:53:12 -06:00
parent a548ce68c1
commit b989b4a89f
6 changed files with 426 additions and 460 deletions
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lfs.h
+29 -27
View File
@@ -45,25 +45,25 @@ typedef int32_t lfs_soff_t;
typedef uint32_t lfs_block_t;
// Maximum name size in bytes, may be redefined to reduce the size of the
// info struct. Limited to <= 8190. Stored in superblock and must be
// info struct. Limited to <= 1022. 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
// Maximum inline file size in bytes, may be redefined to limit RAM usage,
// but littlefs will automatically limit the LFS_INLINE_MAX to the
// configured cache_size. Limited to <= 8190. Stored in superblock and must
// configured cache_size. Limited to <= 1022. Stored in superblock and must
// be respected by other littlefs drivers.
#ifndef LFS_INLINE_MAX
#define LFS_INLINE_MAX 0x1ffe
#define LFS_INLINE_MAX 1022
#endif
// Maximum size of custom attributes in bytes, may be redefined, but there is
// no real benefit to using a smaller LFS_ATTR_MAX. Limited to <= 8190. Stored
// no real benefit to using a smaller LFS_ATTR_MAX. Limited to <= 1022. Stored
// in superblock and must be respected by other littlefs drivers.
#ifndef LFS_ATTR_MAX
#define LFS_ATTR_MAX 0x1ffe
#define LFS_ATTR_MAX 1022
#endif
// Maximum size of a file in bytes, may be redefined to limit to support other
@@ -98,31 +98,33 @@ enum lfs_error {
// File types
enum lfs_type {
// file types
LFS_TYPE_REG = 0x011,
LFS_TYPE_DIR = 0x010,
LFS_TYPE_REG = 0x001,
LFS_TYPE_DIR = 0x002,
// internally used types
LFS_TYPE_USERATTR = 0x100,
LFS_TYPE_CREATE = 0x000,
LFS_TYPE_DELETE = 0x020,
LFS_TYPE_STRUCT = 0x040,
LFS_TYPE_TAIL = 0x080,
LFS_TYPE_SOFTTAIL = 0x080,
LFS_TYPE_HARDTAIL = 0x081,
LFS_TYPE_CRC = 0x0a0,
LFS_TYPE_SUPERBLOCK = 0x001,
LFS_TYPE_GLOBALS = 0x0e0,
LFS_TYPE_SPLICE = 0x400,
LFS_TYPE_NAME = 0x000,
LFS_TYPE_STRUCT = 0x200,
LFS_TYPE_USERATTR = 0x300,
LFS_TYPE_FROM = 0x100,
LFS_TYPE_TAIL = 0x600,
LFS_TYPE_GLOBALS = 0x700,
LFS_TYPE_CRC = 0x500,
LFS_TYPE_DIRSTRUCT = 0x040,
LFS_TYPE_INLINESTRUCT = 0x041,
LFS_TYPE_CTZSTRUCT = 0x042,
// internally used type specializations
LFS_TYPE_CREATE = 0x401,
LFS_TYPE_DELETE = 0x4ff,
LFS_TYPE_SUPERBLOCK = 0x0ff,
LFS_TYPE_DIRSTRUCT = 0x200,
LFS_TYPE_CTZSTRUCT = 0x202,
LFS_TYPE_INLINESTRUCT = 0x201,
LFS_TYPE_SOFTTAIL = 0x600,
LFS_TYPE_HARDTAIL = 0x601,
LFS_TYPE_MOVESTATE = 0x7ff,
// internal chip sources
LFS_TYPE_FROM = 0x060,
LFS_FROM_MEM = 0x000,
LFS_FROM_DISK = 0x200,
LFS_FROM_MOVE = 0x061,
LFS_FROM_USERATTRS = 0x062,
LFS_FROM_MOVE = 0x101,
LFS_FROM_USERATTRS = 0x102,
};
// File open flags
@@ -314,8 +316,8 @@ typedef struct lfs_cache {
typedef struct lfs_mdir {
lfs_block_t pair[2];
uint32_t rev;
uint32_t etag;
lfs_off_t off;
uint32_t etag;
uint16_t count;
bool erased;
bool split;