[PATCH v3 10/26] read-cache: new flag CE_WATCHED to mark what file is watched
- From
Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
- Date
- Feb 3, 2014, 04:28 UTC
- Message-ID
- <1391401754-15347-11-git-send-email-pclouds@gmail.com>
- In-Reply-To
- <1391401754-15347-1-git-send-email-pclouds@gmail.com>
This bit is basically "dynamic CE_VALID". It marks entries that are being watched by the incoming file-watcher. When an index is loaded, file watcher is contacted and the list of updated paths is retrieved.
These paths will have CE_WATCHED cleared and lstat() will be called on them. Those that have CE_WATCHED and not in the list will have CE_VALID turn on to skip lstat(). The setting is temporarily, CE_VALID is not saved to disk if CE_WATCHED is also set.
We keep the CE_WATCHED in a new extension, separated from the entries to save some space because extended ce_flags adds 2 bytes per entry and this flag would be present in the majority of entries. When stored as bitmap, this extension could compress very well with ewah algorithm.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> --- Documentation/technical/index-format.txt | 6 +++++ cache.h | 3 +++ read-cache.c | 41 +++++++++++++++++++++++++++++++- 3 files changed, 49 insertions(+), 1 deletion(-)
diff --git a/Documentation/technical/index-format.txt b/Documentation/technical/index-format.txt index f352a9b..24fd0ae 100644 --- a/Documentation/technical/index-format.txt +++ b/Documentation/technical/index-format.txt @@ -198,3 +198,9 @@ Git index format - At most three 160-bit object names of the entry in stages from 1 to 3 (nothing is written for a missing stage). +=== File watcher + + The signature of this extension is { 'W', 'A', 'T', 'C' }. + + - A bit map of all entries in the index, n-th bit of m-th byte + corresponds to CE_WATCHED of the <m * 8+ n>-th index entry. diff --git a/cache.h b/cache.h index f14d535..a0af2a5 100644 --- a/cache.h +++ b/cache.h @@ -169,6 +169,9 @@ struct cache_entry { /* used to temporarily mark paths matched by pathspecs */ #define CE_MATCHED (1 << 26) +/* set CE_VALID at runtime if the entry is guaranteed not updated */ +#define CE_WATCHED (1 << 27) + /* * Extended on-disk flags */ diff --git a/read-cache.c b/read-cache.c index 3b6daf1..098d3b6 100644 --- a/read-cache.c +++ b/read-cache.c @@ -33,6 +33,7 @@ static struct cache_entry *refresh_cache_entry(struct cache_entry *ce, int reall #define CACHE_EXT(s) ( (s[0]<<24)|(s[1]<<16)|(s[2]<<8)|(s[3]) ) #define CACHE_EXT_TREE 0x54524545 /* "TREE" */ #define CACHE_EXT_RESOLVE_UNDO 0x52455543 /* "REUC" */ +#define CACHE_EXT_WATCH 0x57415443 /* "WATC" */ struct index_state the_index; @@ -1289,6 +1290,19 @@ static int verify_hdr(struct cache_header *hdr, return 0; } +static void read_watch_extension(struct index_state *istate, uint8_t *data, + unsigned long sz) +{ + int i; + if ((istate->cache_nr + 7) / 8 != sz) { + error("invalid 'WATC' extension"); + return; + } + for (i = 0; i < istate->cache_nr; i++) + if (data[i / 8] & (1 << (i % 8))) + istate->cache[i]->ce_flags |= CE_WATCHED; +} + static int read_index_extension(struct index_state *istate, const char *ext, void *data, unsigned long sz) { @@ -1299,6 +1313,9 @@ static int read_index_extension(struct index_state *istate, case CACHE_EXT_RESOLVE_UNDO: istate->resolve_undo = resolve_undo_read(data, sz); break; + case CACHE_EXT_WATCH: + read_watch_extension(istate, data, sz); + break; default: if (*ext < 'A' || 'Z' < *ext) return error("index uses %.4s extension, which we do not understand", @@ -1777,7 +1794,7 @@ int write_index(struct index_state *istate, int newfd) { git_SHA_CTX c; struct cache_header hdr; - int i, err, removed, extended, hdr_version; + int i, err, removed, extended, hdr_version, has_watches = 0; struct cache_entry **cache = istate->cache; int entries = istate->cache_nr; struct stat st; @@ -1786,6 +1803,8 @@ int write_index(struct index_state *istate, int newfd) for (i = removed = extended = 0; i < entries; i++) { if (cache[i]->ce_flags & CE_REMOVE) removed++; + else if (cache[i]->ce_flags & CE_WATCHED) + has_watches++; /* reduce extended entries if possible */ cache[i]->ce_flags &= ~CE_EXTENDED; @@ -1857,6 +1876,26 @@ int write_index(struct index_state *istate, int newfd) if (err) return -1; } + if (has_watches) { + int id, sz = (entries - removed + 7) / 8; + uint8_t *data = xmalloc(sz); + memset(data, 0, sz); + for (i = 0, id = 0; i < entries && has_watches; i++) { + struct cache_entry *ce = cache[i]; + if (ce->ce_flags & CE_REMOVE) + continue; + if (ce->ce_flags & CE_WATCHED) { + data[id / 8] |= 1 << (id % 8); + has_watches--; + } + id++; + } + err = write_index_ext_header(&c, newfd, CACHE_EXT_WATCH, sz) < 0 + || ce_write(&c, newfd, data, sz) < 0; + free(data); + if (err) + return -1; + } if (ce_flush(&c, newfd) || fstat(newfd, &st)) return -1;
-- 1.8.5.2.240.g8478abd