Skip to content

Commit

Permalink
Extend index to save more flags
Browse files Browse the repository at this point in the history 
The on-disk format of index only saves 16 bit flags, nearly all have
been used. The last bit (CE_EXTENDED) is used to for future extension.

This patch extends index entry format to save more flags in future.
The new entry format will be used when CE_EXTENDED bit is 1.

Because older implementation may not understand CE_EXTENDED bit and
misread the new format, if there is any extended entry in index, index
header version will turn 3, which makes it incompatible for older git.
If there is none, header version will return to 2 again.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
  • Loading branch information
Nguyễn Thái Ngọc Duy authored and Shawn O. Pearce committed Oct 12, 2008
1 parent 5c283eb commit 06aaaa0
Show file tree
Hide file tree
Showing 2 changed files with 95 additions and 14 deletions.
58 changes: 54 additions & 4 deletions cache.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -115,6 +115,26 @@ struct ondisk_cache_entry {
char name[FLEX_ARRAY]; /* more */
};

/*
* This struct is used when CE_EXTENDED bit is 1
* The struct must match ondisk_cache_entry exactly from
* ctime till flags
*/
struct ondisk_cache_entry_extended {
struct cache_time ctime;
struct cache_time mtime;
unsigned int dev;
unsigned int ino;
unsigned int mode;
unsigned int uid;
unsigned int gid;
unsigned int size;
unsigned char sha1[20];
unsigned short flags;
unsigned short flags2;
char name[FLEX_ARRAY]; /* more */
};

struct cache_entry {
unsigned int ce_ctime;
unsigned int ce_mtime;
Expand All @@ -136,7 +156,15 @@ struct cache_entry {
#define CE_VALID (0x8000)
#define CE_STAGESHIFT 12

/* In-memory only */
/*
* Range 0xFFFF0000 in ce_flags is divided into
* two parts: in-memory flags and on-disk ones.
* Flags in CE_EXTENDED_FLAGS will get saved on-disk
* if you want to save a new flag, add it in
* CE_EXTENDED_FLAGS
*
* In-memory only flags
*/
#define CE_UPDATE (0x10000)
#define CE_REMOVE (0x20000)
#define CE_UPTODATE (0x40000)
Expand All @@ -145,6 +173,24 @@ struct cache_entry {
#define CE_HASHED (0x100000)
#define CE_UNHASHED (0x200000)

/*
* Extended on-disk flags
*/
/* CE_EXTENDED2 is for future extension */
#define CE_EXTENDED2 0x80000000

#define CE_EXTENDED_FLAGS (0)

/*
* Safeguard to avoid saving wrong flags:
* - CE_EXTENDED2 won't get saved until its semantic is known
* - Bits in 0x0000FFFF have been saved in ce_flags already
* - Bits in 0x003F0000 are currently in-memory flags
*/
#if CE_EXTENDED_FLAGS & 0x803FFFFF
#error "CE_EXTENDED_FLAGS out of range"
#endif

/*
* Copy the sha1 and stat state of a cache entry from one to
* another. But we never change the name, or the hash state!
Expand Down Expand Up @@ -177,7 +223,9 @@ static inline size_t ce_namelen(const struct cache_entry *ce)
}

#define ce_size(ce) cache_entry_size(ce_namelen(ce))
#define ondisk_ce_size(ce) ondisk_cache_entry_size(ce_namelen(ce))
#define ondisk_ce_size(ce) (((ce)->ce_flags & CE_EXTENDED) ? \
ondisk_cache_entry_extended_size(ce_namelen(ce)) : \
ondisk_cache_entry_size(ce_namelen(ce)))
#define ce_stage(ce) ((CE_STAGEMASK & (ce)->ce_flags) >> CE_STAGESHIFT)
#define ce_uptodate(ce) ((ce)->ce_flags & CE_UPTODATE)
#define ce_mark_uptodate(ce) ((ce)->ce_flags |= CE_UPTODATE)
Expand Down Expand Up @@ -220,8 +268,10 @@ static inline int ce_to_dtype(const struct cache_entry *ce)
(S_ISREG(mode) ? (S_IFREG | ce_permissions(mode)) : \
S_ISLNK(mode) ? S_IFLNK : S_ISDIR(mode) ? S_IFDIR : S_IFGITLINK)

#define cache_entry_size(len) ((offsetof(struct cache_entry,name) + (len) + 8) & ~7)
#define ondisk_cache_entry_size(len) ((offsetof(struct ondisk_cache_entry,name) + (len) + 8) & ~7)
#define flexible_size(STRUCT,len) ((offsetof(struct STRUCT,name) + (len) + 8) & ~7)
#define cache_entry_size(len) flexible_size(cache_entry,len)
#define ondisk_cache_entry_size(len) flexible_size(ondisk_cache_entry,len)
#define ondisk_cache_entry_extended_size(len) flexible_size(ondisk_cache_entry_extended,len)

struct index_state {
struct cache_entry **cache;
Expand Down
51 changes: 41 additions & 10 deletions read-cache.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1098,7 +1098,7 @@ static int verify_hdr(struct cache_header *hdr, unsigned long size)

if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
return error("bad signature");
if (hdr->hdr_version != htonl(2))
if (hdr->hdr_version != htonl(2) && hdr->hdr_version != htonl(3))
return error("bad index version");
git_SHA1_Init(&c);
git_SHA1_Update(&c, hdr, size - 20);
Expand Down Expand Up @@ -1133,6 +1133,7 @@ int read_index(struct index_state *istate)
static void convert_from_disk(struct ondisk_cache_entry *ondisk, struct cache_entry *ce)
{
size_t len;
const char *name;

ce->ce_ctime = ntohl(ondisk->ctime.sec);
ce->ce_mtime = ntohl(ondisk->mtime.sec);
Expand All @@ -1145,19 +1146,31 @@ static void convert_from_disk(struct ondisk_cache_entry *ondisk, struct cache_en
/* On-disk flags are just 16 bits */
ce->ce_flags = ntohs(ondisk->flags);

/* For future extension: we do not understand this entry yet */
if (ce->ce_flags & CE_EXTENDED)
die("Unknown index entry format");
hashcpy(ce->sha1, ondisk->sha1);

len = ce->ce_flags & CE_NAMEMASK;

if (ce->ce_flags & CE_EXTENDED) {
struct ondisk_cache_entry_extended *ondisk2;
int extended_flags;
ondisk2 = (struct ondisk_cache_entry_extended *)ondisk;
extended_flags = ntohs(ondisk2->flags2) << 16;
/* We do not yet understand any bit out of CE_EXTENDED_FLAGS */
if (extended_flags & ~CE_EXTENDED_FLAGS)
die("Unknown index entry format %08x", extended_flags);
ce->ce_flags |= extended_flags;
name = ondisk2->name;
}
else
name = ondisk->name;

if (len == CE_NAMEMASK)
len = strlen(ondisk->name);
len = strlen(name);
/*
* NEEDSWORK: If the original index is crafted, this copy could
* go unchecked.
*/
memcpy(ce->name, ondisk->name, len + 1);
memcpy(ce->name, name, len + 1);
}

static inline size_t estimate_cache_size(size_t ondisk_size, unsigned int entries)
Expand Down Expand Up @@ -1417,6 +1430,7 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce)
{
int size = ondisk_ce_size(ce);
struct ondisk_cache_entry *ondisk = xcalloc(1, size);
char *name;

ondisk->ctime.sec = htonl(ce->ce_ctime);
ondisk->ctime.nsec = 0;
Expand All @@ -1430,7 +1444,15 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce)
ondisk->size = htonl(ce->ce_size);
hashcpy(ondisk->sha1, ce->sha1);
ondisk->flags = htons(ce->ce_flags);
memcpy(ondisk->name, ce->name, ce_namelen(ce));
if (ce->ce_flags & CE_EXTENDED) {
struct ondisk_cache_entry_extended *ondisk2;
ondisk2 = (struct ondisk_cache_entry_extended *)ondisk;
ondisk2->flags2 = htons((ce->ce_flags & CE_EXTENDED_FLAGS) >> 16);
name = ondisk2->name;
}
else
name = ondisk->name;
memcpy(name, ce->name, ce_namelen(ce));

return ce_write(c, fd, ondisk, size);
}
Expand All @@ -1439,16 +1461,25 @@ int write_index(const struct index_state *istate, int newfd)
{
git_SHA_CTX c;
struct cache_header hdr;
int i, err, removed;
int i, err, removed, extended;
struct cache_entry **cache = istate->cache;
int entries = istate->cache_nr;

for (i = removed = 0; i < entries; i++)
for (i = removed = extended = 0; i < entries; i++) {
if (cache[i]->ce_flags & CE_REMOVE)
removed++;

/* reduce extended entries if possible */
cache[i]->ce_flags &= ~CE_EXTENDED;
if (cache[i]->ce_flags & CE_EXTENDED_FLAGS) {
extended++;
cache[i]->ce_flags |= CE_EXTENDED;
}
}

hdr.hdr_signature = htonl(CACHE_SIGNATURE);
hdr.hdr_version = htonl(2);
/* for extended format, increase version so older git won't try to read it */
hdr.hdr_version = htonl(extended ? 3 : 2);
hdr.hdr_entries = htonl(entries - removed);

git_SHA1_Init(&c);
Expand Down

0 comments on commit 06aaaa0

Please sign in to comment.