#include "cache.h"
struct cache_entry **active_cache = NULL;
+static time_t index_file_timestamp;
unsigned int active_nr = 0, active_alloc = 0, active_cache_changed = 0;
/*
ce->ce_size = htonl(st->st_size);
}
-int ce_match_stat(struct cache_entry *ce, struct stat *st)
+static int ce_compare_data(struct cache_entry *ce, struct stat *st)
+{
+ int match = -1;
+ int fd = open(ce->name, O_RDONLY);
+
+ if (fd >= 0) {
+ unsigned char sha1[20];
+ if (!index_fd(sha1, fd, st, 0, NULL))
+ match = memcmp(sha1, ce->sha1, 20);
+ close(fd);
+ }
+ return match;
+}
+
+static int ce_compare_link(struct cache_entry *ce, unsigned long expected_size)
+{
+ int match = -1;
+ char *target;
+ void *buffer;
+ unsigned long size;
+ char type[10];
+ int len;
+
+ target = xmalloc(expected_size);
+ len = readlink(ce->name, target, expected_size);
+ if (len != expected_size) {
+ free(target);
+ return -1;
+ }
+ buffer = read_sha1_file(ce->sha1, type, &size);
+ if (!buffer) {
+ free(target);
+ return -1;
+ }
+ if (size == expected_size)
+ match = memcmp(buffer, target, size);
+ free(buffer);
+ free(target);
+ return match;
+}
+
+static int ce_modified_check_fs(struct cache_entry *ce, struct stat *st)
+{
+ switch (st->st_mode & S_IFMT) {
+ case S_IFREG:
+ if (ce_compare_data(ce, st))
+ return DATA_CHANGED;
+ break;
+ case S_IFLNK:
+ if (ce_compare_link(ce, st->st_size))
+ return DATA_CHANGED;
+ break;
+ default:
+ return TYPE_CHANGED;
+ }
+ return 0;
+}
+
+static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
{
unsigned int changed = 0;
if (ce->ce_size != htonl(st->st_size))
changed |= DATA_CHANGED;
+
return changed;
}
-static int ce_compare_data(struct cache_entry *ce, struct stat *st)
+int ce_match_stat(struct cache_entry *ce, struct stat *st)
{
- int match = -1;
- int fd = open(ce->name, O_RDONLY);
+ unsigned int changed = ce_match_stat_basic(ce, st);
- if (fd >= 0) {
- unsigned char sha1[20];
- if (!index_fd(sha1, fd, st, 0, NULL))
- match = memcmp(sha1, ce->sha1, 20);
- close(fd);
- }
- return match;
-}
-
-static int ce_compare_link(struct cache_entry *ce, unsigned long expected_size)
-{
- int match = -1;
- char *target;
- void *buffer;
- unsigned long size;
- char type[10];
- int len;
+ /*
+ * Within 1 second of this sequence:
+ * echo xyzzy >file && git-update-index --add file
+ * running this command:
+ * echo frotz >file
+ * would give a falsely clean cache entry. The mtime and
+ * length match the cache, and other stat fields do not change.
+ *
+ * We could detect this at update-index time (the cache entry
+ * being registered/updated records the same time as "now")
+ * and delay the return from git-update-index, but that would
+ * effectively mean we can make at most one commit per second,
+ * which is not acceptable. Instead, we check cache entries
+ * whose mtime are the same as the index file timestamp more
+ * careful than others.
+ */
+ if (!changed &&
+ index_file_timestamp &&
+ index_file_timestamp <= ntohl(ce->ce_mtime.sec))
+ changed |= ce_modified_check_fs(ce, st);
- target = xmalloc(expected_size);
- len = readlink(ce->name, target, expected_size);
- if (len != expected_size) {
- free(target);
- return -1;
- }
- buffer = read_sha1_file(ce->sha1, type, &size);
- if (!buffer) {
- free(target);
- return -1;
- }
- if (size == expected_size)
- match = memcmp(buffer, target, size);
- free(buffer);
- free(target);
- return match;
+ return changed;
}
int ce_modified(struct cache_entry *ce, struct stat *st)
{
- int changed;
+ int changed, changed_fs;
changed = ce_match_stat(ce, st);
if (!changed)
return 0;
-
/*
* If the mode or type has changed, there's no point in trying
* to refresh the entry - it's not going to match
if ((changed & DATA_CHANGED) && ce->ce_size != htonl(0))
return changed;
- switch (st->st_mode & S_IFMT) {
- case S_IFREG:
- if (ce_compare_data(ce, st))
- return changed | DATA_CHANGED;
- break;
- case S_IFLNK:
- if (ce_compare_link(ce, st->st_size))
- return changed | DATA_CHANGED;
- break;
- default:
- return changed | TYPE_CHANGED;
- }
+ changed_fs = ce_modified_check_fs(ce, st);
+ if (changed_fs)
+ return changed | changed_fs;
return 0;
}
return active_nr;
errno = ENOENT;
+ index_file_timestamp = 0;
fd = open(get_index_file(), O_RDONLY);
if (fd < 0) {
if (errno == ENOENT)
offset = offset + ce_size(ce);
active_cache[i] = ce;
}
+ index_file_timestamp = st.st_mtime;
return active_nr;
unmap:
return 0;
}
+static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
+{
+ /*
+ * The only thing we care about in this function is to smudge the
+ * falsely clean entry due to touch-update-touch race, so we leave
+ * everything else as they are. We are called for entries whose
+ * ce_mtime match the index file mtime.
+ */
+ struct stat st;
+
+ if (lstat(ce->name, &st) < 0)
+ return;
+ if (ce_match_stat_basic(ce, &st))
+ return;
+ if (ce_modified_check_fs(ce, &st)) {
+ /* This is "racily clean"; smudge it. Note that this
+ * is a tricky code. At first glance, it may appear
+ * that it can break with this sequence:
+ *
+ * $ echo xyzzy >frotz
+ * $ git-update-index --add frotz
+ * $ : >frotz
+ * $ sleep 3
+ * $ echo filfre >nitfol
+ * $ git-update-index --add nitfol
+ *
+ * but it does not. Whe the second update-index runs,
+ * it notices that the entry "frotz" has the same timestamp
+ * as index, and if we were to smudge it by resetting its
+ * size to zero here, then the object name recorded
+ * in index is the 6-byte file but the cached stat information
+ * becomes zero --- which would then match what we would
+ * obtain from the filesystem next time we stat("frotz").
+ *
+ * However, the second update-index, before calling
+ * this function, notices that the cached size is 6
+ * bytes and what is on the filesystem is an empty
+ * file, and never calls us, so the cached size information
+ * for "frotz" stays 6 which does not match the filesystem.
+ */
+ ce->ce_size = htonl(0);
+ }
+}
+
int write_cache(int newfd, struct cache_entry **cache, int entries)
{
SHA_CTX c;
struct cache_entry *ce = cache[i];
if (!ce->ce_mode)
continue;
+ if (index_file_timestamp &&
+ index_file_timestamp <= ntohl(ce->ce_mtime.sec))
+ ce_smudge_racily_clean_entry(ce);
if (ce_write(&c, newfd, ce, ce_size(ce)) < 0)
return -1;
}