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[PATCH 2/6] sha1_file: fix error message for alternate objects

From
Jeff King <peff@peff.net>
Date
Jan 13, 2017, 17:54 UTC
Message-ID
<20170113175439.jedroszyilb6idrd@sigill.intra.peff.net>
In-Reply-To
<20170113175258.e66taigy4wpokohk@sigill.intra.peff.net>

When we fail to open a corrupt loose object, we report an error and mention the filename via sha1_file_name(). However, that function will always give us a path in the local repository, whereas the corrupt object may have come from an alternate. The result is a very misleading error message.

Teach the open_sha1_file() and stat_sha1_file() helpers to pass back the path they found, so that we can report it correctly.

Note that the pointers we return go to static storage (e.g., from sha1_file_name()), which is slightly dangerous. However, these helpers are static local helpers, and the names are used for immediately generating error messages. The simplicity is an acceptable tradeoff for the danger.

Signed-off-by: Jeff King <peff@peff.net>
---
 sha1_file.c     | 46 +++++++++++++++++++++++++++++++---------------
 t/t1450-fsck.sh | 10 ++++++++++
 2 files changed, 41 insertions(+), 15 deletions(-)
diff --git a/sha1_file.c b/sha1_file.c
index 1eb47f611..c6b990f41 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1630,39 +1630,54 @@ int git_open_cloexec(const char *name, int flags)
 	return fd;
 }
 
-static int stat_sha1_file(const unsigned char *sha1, struct stat *st)
+/*
+ * Find "sha1" as a loose object in the local repository or in an alternate.
+ * Returns 0 on success, negative on failure.
+ *
+ * The "path" out-parameter will give the path of the object we found (if any).
+ * Note that it may point to static storage and is only valid until another
+ * call to sha1_file_name(), etc.
+ */
+static int stat_sha1_file(const unsigned char *sha1, struct stat *st,
+			  const char **path)
 {
 	struct alternate_object_database *alt;
 
-	if (!lstat(sha1_file_name(sha1), st))
+	*path = sha1_file_name(sha1);
+	if (!lstat(*path, st))
 		return 0;
 
 	prepare_alt_odb();
 	errno = ENOENT;
 	for (alt = alt_odb_list; alt; alt = alt->next) {
-		const char *path = alt_sha1_path(alt, sha1);
-		if (!lstat(path, st))
+		*path = alt_sha1_path(alt, sha1);
+		if (!lstat(*path, st))
 			return 0;
 	}
 
 	return -1;
 }
 
-static int open_sha1_file(const unsigned char *sha1)
+/*
+ * Like stat_sha1_file(), but actually open the object and return the
+ * descriptor. See the caveats on the "path" parameter above.
+ */
+static int open_sha1_file(const unsigned char *sha1, const char **path)
 {
 	int fd;
 	struct alternate_object_database *alt;
 	int most_interesting_errno;
 
-	fd = git_open(sha1_file_name(sha1));
+	*path = sha1_file_name(sha1);
+	fd = git_open(*path);
 	if (fd >= 0)
 		return fd;
 	most_interesting_errno = errno;
 
 	prepare_alt_odb();
 	for (alt = alt_odb_list; alt; alt = alt->next) {
-		const char *path = alt_sha1_path(alt, sha1);
-		fd = git_open(path);
+		*path = alt_sha1_path(alt, sha1);
+		fd = git_open(*path);
 		if (fd >= 0)
 			return fd;
 		if (most_interesting_errno == ENOENT)
@@ -1674,10 +1689,11 @@ static int open_sha1_file(const unsigned char *sha1)
 
 void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 {
+	const char *path;
 	void *map;
 	int fd;
 
-	fd = open_sha1_file(sha1);
+	fd = open_sha1_file(sha1, &path);
 	map = NULL;
 	if (fd >= 0) {
 		struct stat st;
@@ -1686,7 +1702,7 @@ void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 			*size = xsize_t(st.st_size);
 			if (!*size) {
 				/* mmap() is forbidden on empty files */
-				error("object file %s is empty", sha1_file_name(sha1));
+				error("object file %s is empty", path);
 				return NULL;
 			}
 			map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
@@ -2806,8 +2822,9 @@ static int sha1_loose_object_info(const unsigned char *sha1,
 	 * object even exists.
 	 */
 	if (!oi->typep && !oi->typename && !oi->sizep) {
+		const char *path;
 		struct stat st;
-		if (stat_sha1_file(sha1, &st) < 0)
+		if (stat_sha1_file(sha1, &st, &path) < 0)
 			return -1;
 		if (oi->disk_sizep)
 			*oi->disk_sizep = st.st_size;
@@ -3003,6 +3020,8 @@ void *read_sha1_file_extended(const unsigned char *sha1,
 {
 	void *data;
 	const struct packed_git *p;
+	const char *path;
+	struct stat st;
 	const unsigned char *repl = lookup_replace_object_extended(sha1, flag);
 
 	errno = 0;
@@ -3018,12 +3037,9 @@ void *read_sha1_file_extended(const unsigned char *sha1,
 		die("replacement %s not found for %s",
 		    sha1_to_hex(repl), sha1_to_hex(sha1));
 
-	if (has_loose_object(repl)) {
-		const char *path = sha1_file_name(sha1);
-
+	if (!stat_sha1_file(repl, &st, &path))
 		die("loose object %s (stored in %s) is corrupt",
 		    sha1_to_hex(repl), path);
-	}
 
 	if ((p = has_packed_and_bad(repl)) != NULL)
 		die("packed object %s (stored in %s) is corrupt",
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index 3297d4cb2..f95174c9d 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -550,4 +550,14 @@ test_expect_success 'fsck --name-objects' '
 	)
 '
 
+test_expect_success 'alternate objects are correctly blamed' '
+	test_when_finished "rm -rf alt.git .git/objects/info/alternates" &&
+	git init --bare alt.git &&
+	echo "../../alt.git/objects" >.git/objects/info/alternates &&
+	mkdir alt.git/objects/12 &&
+	>alt.git/objects/12/34567890123456789012345678901234567890 &&
+	test_must_fail git fsck >out 2>&1 &&
+	grep alt.git out
+'
+
 test_done

-- 
2.11.0.629.g10075098c
Previous: Jeff KingNext: Jeff King
Message 7 of 39 in “"git fsck" not detecting garbage at the end of blob object files...”
  1. John SzakmeisterJan 7, 2017
  2. Dennis KaarsemakerJan 7, 2017
  3. Jeff KingJan 8, 2017
  4. John SzakmeisterJan 13, 2017
  5. 0/6 loose-object fsck fixes/tighteningJeff King, Jan 13, 2017
  6. 1/6 t1450: refactor loose-object removalJeff King, Jan 13, 2017
  7. 2/6 sha1_file: fix error message for alternate objectsJeff King, Jan 13, 2017
  8. 3/6 t1450: test fsck of packed objectsJeff King, Jan 13, 2017
  9. 4/6 sha1_file: add read_loose_object() functionJeff King, Jan 13, 2017
  10. 5/6 fsck: parse loose object paths directlyJeff King, Jan 13, 2017
  11. Infinite loop regression in git-fsck in v2.12.0Ævar Arnfjörð Bjarmason, Oct 30, 2018
  12. Jeff KingOct 30, 2018
  13. Junio C HamanoOct 30, 2018
  14. Jeff KingOct 30, 2018
  15. Jeff KingOct 30, 2018
  16. 1/3 t1450: check large blob in trailing-garbage testJeff King, Oct 30, 2018
  17. 2/3 check_stream_sha1(): handle input underflowJeff King, Oct 30, 2018
  18. Junio C HamanoOct 31, 2018
  19. Jeff KingOct 31, 2018
  20. Junio C HamanoOct 31, 2018
  21. Jeff KingOct 31, 2018
  22. Jeff KingOct 31, 2018
  23. Junio C HamanoOct 31, 2018
  24. 3/3 cat-file: handle streaming failures consistentlyJeff King, Oct 30, 2018
  25. 0/3 Add a GIT_TEST_FSCK test modeÆvar Arnfjörð Bjarmason, Oct 31, 2018
  26. 1/3 tests: add a "env-bool" helper to test-toolÆvar Arnfjörð Bjarmason, Oct 31, 2018
  27. 2/3 tests: mark those tests where "git fsck" fails at the endÆvar Arnfjörð Bjarmason, Oct 31, 2018
  28. Junio C HamanoNov 1, 2018
  29. 3/3 tests: add a special test setup that runs "git fsck" before exitingÆvar Arnfjörð Bjarmason, Oct 31, 2018
  30. Torsten BögershausenOct 31, 2018
  31. Junio C HamanoOct 31, 2018
  32. Jeff KingOct 31, 2018
  33. Eric SunshineOct 31, 2018
  34. Jeff KingOct 31, 2018
  35. Ævar Arnfjörð BjarmasonOct 30, 2018
  36. Jeff KingOct 30, 2018
  37. 6/6 fsck: detect trailing garbage in all object typesJeff King, Jan 13, 2017
  38. John SzakmeisterJan 19, 2017
  39. John SzakmeisterJan 13, 2017

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