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Added rudimentary framework for journaling metadata pairs

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This is a big change stemming from the fact that resizable entries
were surprisingly complicated to implement and came in with a sizable
code cost.

The theory is that the journalling has a comparable cost to resizable
entries. Both need to handle overflowing blocks, and managing offsets is
comparable to managing attribute IDs. But by jumping all the way to full
journaling, we can statically wear-level the metadata written to
metadata pairs.

The idea of journaling littlefs's metadata has been mentioned several times in
discussions and fits well into how littlefs works. You could even view the
existing metadata log as a log of size 2.

The downside of this approach is that changing the metadata in this way
would break compatibility from the existing layout on disk. Something
that resizable entries does not do.

That being said, adopting journaling at the metadata layer offers a big
improvement to littlefs's performance and wear-leveling, with very
little cost (maybe even none or negative after resizable entries?).
This commit is contained in:
Christopher Haster
2018-05-19 18:25:47 -05:00
parent 61f454b008
commit 8070abec34
3 changed files with 966 additions and 5 deletions
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57
lfs.h
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@@ -27,14 +27,14 @@
// 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 0x00020000
#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 0x00020000
#define LFS_DISK_VERSION_MAJOR (0xffff & (LFS_DISK_VERSION >> 16))
#define LFS_DISK_VERSION_MINOR (0xffff & (LFS_DISK_VERSION >> 0))
@@ -105,6 +105,33 @@ enum lfs_type {
LFS_STRUCT_DIR = 0x20,
LFS_STRUCT_INLINE = 0x30,
LFS_STRUCT_MOVED = 0x80,
// file type
LFS_TYPE_REG_ = 0x020,
LFS_TYPE_DIR_ = 0x030,
LFS_TYPE_NAME_ = 0x010,
LFS_TYPE_MOVE_ = 0x060,
LFS_TYPE_DROP_ = 0x070,
LFS_TYPE_SUPERBLOCK_ = 0x0c0,
LFS_TYPE_TAIL_ = 0x0d0,
LFS_TYPE_CRC_ = 0x0e0,
// on disk structure
LFS_STRUCT_ATTR_ = 0x100,
LFS_STRUCT_INLINE_ = 0x000,
LFS_STRUCT_CTZ_ = 0x00c,
LFS_STRUCT_DIR_ = 0x008,
// LFS_TYPE_DIR_ = 0x002,
// LFS_TYPE_SUPERBLOCK_ = 0xff2,
// LFS_MASK_ID_ = 0xff000000,
// LFS_MASK_TYPE_ = 0x00fff000,
// LFS_MASK_ATTR_ = 0x00ff0000,
// LFS_MASK_STRUCT_ = 0x0000f000,
// LFS_MASK_SIZE_ = 0x00000fff,
};
// File open flags
@@ -267,6 +294,21 @@ typedef struct lfs_entry {
} d;
} lfs_entry_t;
typedef struct lfs_entry_ {
uint32_t tag;
union {
lfs_block_t pair[2];
struct {
lfs_block_t head;
lfs_size_t size;
} ctz;
struct {
lfs_block_t block;
lfs_off_t off;
} d;
} u;
} lfs_entry_t_;
typedef struct lfs_entry_attr {
struct lfs_disk_entry_attr {
uint8_t type;
@@ -314,6 +356,17 @@ typedef struct lfs_dir {
} d;
} lfs_dir_t;
typedef struct lfs_dir_ {
lfs_block_t pair[2];
lfs_block_t tail[2];
uint32_t rev;
lfs_off_t off;
uint32_t etag;
uint16_t count;
bool erased;
} lfs_dir_t_;
typedef struct lfs_superblock {
struct lfs_disk_superblock {
lfs_block_t root[2];