[PATCH] Make nsec checking optional

The nsec field of ctime/mtime is now checked only with -DNSEC defined during
compilation. nsec acts broken since it is stored in the icache but apparently
just gets to zero when flushed to filesystem not supporting it (e.g. ext3),
creating illusions of false changes. At least that's my impression.

Signed-off-by: Petr Baudis <pasky@ucw.cz>

Makefile

@@ -1,10 +1,17 @@
 # -DCOLLISION_CHECK if you believe that SHA1's
 # 1461501637330902918203684832716283019655932542976 hashes do not give you
 # enough guarantees about no collisions between objects ever hapenning.
+#
+# -DNSEC if you want git to care about sub-second file mtimes and ctimes.
+# Note that you need some new glibc (at least >2.2.4) for this, and it will
+# BREAK YOUR LOCAL DIFFS! show-diff and anything using it will likely randomly
+# break unless your underlying filesystem supports those sub-second times
+# (my ext3 doesn't).
 CFLAGS=-g -O3 -Wall
 
 CC=gcc
 
+
 PROG=   update-cache show-diff init-db write-tree read-tree commit-tree \
 	cat-file fsck-cache checkout-cache diff-tree rev-tree show-files \
 	check-files ls-tree

read-cache.c

@@ -250,11 +250,20 @@ int cache_match_stat(struct cache_entry *ce, struct stat *st)
 {
 	unsigned int changed = 0;
 
-	if (ce->mtime.sec  != (unsigned int)st->st_mtim.tv_sec ||
-	    ce->mtime.nsec != (unsigned int)st->st_mtim.tv_nsec)
+	/* nsec seems unreliable - not all filesystems support it, so
+	 * as long as it is in the inode cache you get right nsec
+	 * but after it gets flushed, you get zero nsec. */
+	if (ce->mtime.sec  != (unsigned int)st->st_mtim.tv_sec
+#ifdef NSEC
+	    || ce->mtime.nsec != (unsigned int)st->st_mtim.tv_nsec
+#endif
+	    )
 		changed |= MTIME_CHANGED;
-	if (ce->ctime.sec  != (unsigned int)st->st_ctim.tv_sec ||
-	    ce->ctime.nsec != (unsigned int)st->st_ctim.tv_nsec)
+	if (ce->ctime.sec  != (unsigned int)st->st_ctim.tv_sec
+#ifdef NSEC
+	    || ce->ctime.nsec != (unsigned int)st->st_ctim.tv_nsec
+#endif
+	    )
 		changed |= CTIME_CHANGED;
 	if (ce->st_uid != (unsigned int)st->st_uid ||
 	    ce->st_gid != (unsigned int)st->st_gid)