mark_fsmonitor_valid(): mark the index as changed if needed

Without this bug fix, t7519's four "status doesn't detect unreported
modifications" test cases would fail occasionally (and, oddly enough,
*a lot* more frequently on Windows).

The reason is that these test cases intentionally use the side effect of
`git status` to re-write the index if any updates were detected: they
first clean the worktree, run `git status` to update the index as well
as show the output to the casual reader, then make the worktree dirty
again and expect no changes to reported if running with a mocked
fsmonitor hook.

The problem with this strategy was that the index was written during
said `git status` on the clean worktree for the *wrong* reason: not
because the index was marked as changed (it wasn't), but because the
recorded mtimes were racy with the index' own mtime.

As the mtime granularity on Windows is 100 nanoseconds (see e.g.
https://docs.microsoft.com/en-us/windows/desktop/SysInfo/file-times),
the mtimes of the files are often enough *not* racy with the index', so
that that `git status` call currently does not always update the index
(including the fsmonitor extension), causing the test case to fail.

The obvious fix: if we change *any* index entry's `CE_FSMONITOR_VALID`
flag, we should also mark the index as changed. That will cause the
index to be written upon `git status`, *including* an updated fsmonitor
extension.

Side note: Even though the reader might think that the t7519 issue
should be *much* more prevalent on Linux, given that the ext4 filesystem
(that seems to be used by every Linux distribution) stores mtimes in
nanosecond precision. However, ext4 uses `current_kernel_time()` (see
https://unix.stackexchange.com/questions/11599#comment762968_11599; it
is *amazingly* hard to find any proper source of information about such
ext4 questions) whose accuracy seems to depend on many factors but is
safely worse than the 100-nanosecond granularity of NTFS (again, it is
*horribly* hard to find anything remotely authoritative about this
question). So it seems that the racy index condition that hid the bug
fixed by this patch simply is a lot more likely on Linux than on
Windows. But not impossible ;-)

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/diff-lib.c b/diff-lib.c
index a838c219ec044b9fb78b4bda058d078e66d7aaf8..61812f48c2737a4702e604962e97f5c00d394b16 100644 (file)
--- a/diff-lib.c
+++ b/diff-lib.c
@@ -232,7 +232,7 @@ int run_diff_files(struct rev_info *revs, unsigned int option)
 
                if (!changed && !dirty_submodule) {
                        ce_mark_uptodate(ce);
-                       mark_fsmonitor_valid(ce);
+                       mark_fsmonitor_valid(istate, ce);
                        if (!revs->diffopt.flags.find_copies_harder)
                                continue;
                }

diff --git a/fsmonitor.h b/fsmonitor.h
index 8489fa3244976bb3e489c030e726cf06f0e4e9b3..739318ab6d1060e3f5ef9eba0ab93aa560c1d246 100644 (file)
--- a/fsmonitor.h
+++ b/fsmonitor.h
@@ -49,9 +49,10 @@ void refresh_fsmonitor(struct index_state *istate);
  * called any time the cache entry has been updated to reflect the
  * current state of the file on disk.
  */
-static inline void mark_fsmonitor_valid(struct cache_entry *ce)
+static inline void mark_fsmonitor_valid(struct index_state *istate, struct cache_entry *ce)
 {
-       if (core_fsmonitor) {
+       if (core_fsmonitor && !(ce->ce_flags & CE_FSMONITOR_VALID)) {
+               istate->cache_changed = 1;
                ce->ce_flags |= CE_FSMONITOR_VALID;
                trace_printf_key(&trace_fsmonitor, "mark_fsmonitor_clean '%s'", ce->name);
        }

diff --git a/preload-index.c b/preload-index.c
index e73600ee7841a299e060369ca9eecf46d5a7fb0f..ed6eaa47388af8d33398e7c9652c622030e75147 100644 (file)
--- a/preload-index.c
+++ b/preload-index.c
@@ -78,7 +78,7 @@ static void *preload_thread(void *_data)
                if (ie_match_stat(index, ce, &st, CE_MATCH_RACY_IS_DIRTY|CE_MATCH_IGNORE_FSMONITOR))
                        continue;
                ce_mark_uptodate(ce);
-               mark_fsmonitor_valid(ce);
+               mark_fsmonitor_valid(index, ce);
        } while (--nr > 0);
        if (p->progress) {
                struct progress_data *pd = p->progress;

diff --git a/read-cache.c b/read-cache.c
index d3b43ae3bad3c053d0d4ef773b9f880699a4f6a0..32816763bd6dbe3d5e1784b3a39bb8c431ec82f9 100644 (file)
--- a/read-cache.c
+++ b/read-cache.c
@@ -204,7 +204,7 @@ void fill_stat_cache_info(struct index_state *istate, struct cache_entry *ce, st
 
        if (S_ISREG(st->st_mode)) {
                ce_mark_uptodate(ce);
-               mark_fsmonitor_valid(ce);
+               mark_fsmonitor_valid(istate, ce);
        }
 }
 
@@ -1432,7 +1432,7 @@ static struct cache_entry *refresh_cache_ent(struct index_state *istate,
                         */
                        if (!S_ISGITLINK(ce->ce_mode)) {
                                ce_mark_uptodate(ce);
-                               mark_fsmonitor_valid(ce);
+                               mark_fsmonitor_valid(istate, ce);
                        }
                        return ce;
                }