From 0cc77c386cea7afebb54a5e7263ca37569ecfe7a Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 27 Feb 2014 05:56:31 -0500 Subject: [PATCH] shallow: use stat_validity to check for up-to-date file When we are about to write the shallow file, we check that it has not changed since we last read it. Instead of hand-rolling this, we can use stat_validity. This is built around the index stat-check, so it is more robust than just checking the mtime, as we do now (it uses the same check as we do for index files). The new code also handles the case of a shallow file appearing unexpectedly. With the current code, two simultaneous processes making us shallow (e.g., two "git fetch --depth=1" running at the same time in a non-shallow repository) can race to overwrite each other. As a bonus, we also remove a race in determining the stat information of what we read (we stat and then open, leaving a race window; instead we should open and then fstat the descriptor). Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- shallow.c | 24 +++++++----------------- 1 file changed, 7 insertions(+), 17 deletions(-) diff --git a/shallow.c b/shallow.c index bbc98b55c0..1a6f022fa8 100644 --- a/shallow.c +++ b/shallow.c @@ -10,7 +10,7 @@ #include "commit-slab.h" static int is_shallow = -1; -static struct stat shallow_stat; +static struct stat_validity shallow_stat; static char *alternate_shallow_file; void set_alternate_shallow_file(const char *path, int override) @@ -52,12 +52,12 @@ int is_repository_shallow(void) * shallow file should be used. We could just open it and it * will likely fail. But let's do an explicit check instead. */ - if (!*path || - stat(path, &shallow_stat) || - (fp = fopen(path, "r")) == NULL) { + if (!*path || (fp = fopen(path, "r")) == NULL) { + stat_validity_clear(&shallow_stat); is_shallow = 0; return is_shallow; } + stat_validity_update(&shallow_stat, fileno(fp)); is_shallow = 1; while (fgets(buf, sizeof(buf), fp)) { @@ -137,21 +137,11 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth, void check_shallow_file_for_update(void) { - struct stat st; - - if (!is_shallow) - return; - else if (is_shallow == -1) + if (is_shallow == -1) die("BUG: shallow must be initialized by now"); - if (stat(git_path("shallow"), &st)) - die("shallow file was removed during fetch"); - else if (st.st_mtime != shallow_stat.st_mtime -#ifdef USE_NSEC - || ST_MTIME_NSEC(st) != ST_MTIME_NSEC(shallow_stat) -#endif - ) - die("shallow file was changed during fetch"); + if (!stat_validity_check(&shallow_stat, git_path("shallow"))) + die("shallow file has changed since we read it"); } #define SEEN_ONLY 1 -- 2.11.4.GIT