X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=read-cache.c;fp=read-cache.c;h=c5474d49758b640f8942b1e3eb1a1c8f47c78ed8;hb=4b3511b0f8422fd2c5b1b37c9655ae2ce904bca5;hp=afdc2b075b00c035c378a6f2ff29de267ff45b4d;hpb=407c8eb0d09d4b84bbfda9e04895a35c8fd6fef6;p=git.git

diff --git a/read-cache.c b/read-cache.c
index afdc2b07..c5474d49 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -616,7 +616,31 @@ static void ce_smudge_racily_clean_entry(struct cache_entry *ce)
 	if (ce_match_stat_basic(ce, &st))
 		return;
 	if (ce_modified_check_fs(ce, &st)) {
-		/* This is "racily clean"; smudge it */
+		/* 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);
 	}
 }