pack-write: fix return parameter of `write_rev_file_order()`

While the return parameter of `write_rev_file_order()` is a string
constant, the function may indeed return an allocated string when its
first parameter is a `NULL` pointer. This makes for a confusing calling
convention, where callers need to be aware of these intricate ownership
rules and cast away the constness to free the string in some cases.

Adapt the function and its caller `write_rev_file()` to always return an
allocated string and adapt callers to always free the return value.

Note that this requires us to also adapt `rename_tmp_packfile()`, which
compares the pointers to packfile data with each other. Now that the
path of the reverse index file gets allocated unconditionally the check
will always fail. This is fixed by using strcmp(3P) instead, which also
feels way less fragile.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 23 insertions, 19 deletions

diff --git a/pack-write.c b/pack-write.c
index 27965672f1..9961149e65 100644
--- a/pack-write.c
+++ b/pack-write.c
@@ -212,15 +212,15 @@ static void write_rev_trailer(struct hashfile *f, const unsigned char *hash)
 	hashwrite(f, hash, the_hash_algo->rawsz);
 }
 
-const char *write_rev_file(const char *rev_name,
-			   struct pack_idx_entry **objects,
-			   uint32_t nr_objects,
-			   const unsigned char *hash,
-			   unsigned flags)
+char *write_rev_file(const char *rev_name,
+		     struct pack_idx_entry **objects,
+		     uint32_t nr_objects,
+		     const unsigned char *hash,
+		     unsigned flags)
 {
 	uint32_t *pack_order;
 	uint32_t i;
-	const char *ret;
+	char *ret;
 
 	if (!(flags & WRITE_REV) && !(flags & WRITE_REV_VERIFY))
 		return NULL;
@@ -238,13 +238,14 @@ const char *write_rev_file(const char *rev_name,
 	return ret;
 }
 
-const char *write_rev_file_order(const char *rev_name,
-				 uint32_t *pack_order,
-				 uint32_t nr_objects,
-				 const unsigned char *hash,
-				 unsigned flags)
+char *write_rev_file_order(const char *rev_name,
+			   uint32_t *pack_order,
+			   uint32_t nr_objects,
+			   const unsigned char *hash,
+			   unsigned flags)
 {
 	struct hashfile *f;
+	char *path;
 	int fd;
 
 	if ((flags & WRITE_REV) && (flags & WRITE_REV_VERIFY))
@@ -254,12 +255,13 @@ const char *write_rev_file_order(const char *rev_name,
 		if (!rev_name) {
 			struct strbuf tmp_file = STRBUF_INIT;
 			fd = odb_mkstemp(&tmp_file, "pack/tmp_rev_XXXXXX");
-			rev_name = strbuf_detach(&tmp_file, NULL);
+			path = strbuf_detach(&tmp_file, NULL);
 		} else {
 			unlink(rev_name);
 			fd = xopen(rev_name, O_CREAT|O_EXCL|O_WRONLY, 0600);
+			path = xstrdup(rev_name);
 		}
-		f = hashfd(fd, rev_name);
+		f = hashfd(fd, path);
 	} else if (flags & WRITE_REV_VERIFY) {
 		struct stat statbuf;
 		if (stat(rev_name, &statbuf)) {
@@ -270,22 +272,24 @@ const char *write_rev_file_order(const char *rev_name,
 				die_errno(_("could not stat: %s"), rev_name);
 		}
 		f = hashfd_check(rev_name);
-	} else
+		path = xstrdup(rev_name);
+	} else {
 		return NULL;
+	}
 
 	write_rev_header(f);
 
 	write_rev_index_positions(f, pack_order, nr_objects);
 	write_rev_trailer(f, hash);
 
-	if (rev_name && adjust_shared_perm(rev_name) < 0)
-		die(_("failed to make %s readable"), rev_name);
+	if (adjust_shared_perm(path) < 0)
+		die(_("failed to make %s readable"), path);
 
 	finalize_hashfile(f, NULL, FSYNC_COMPONENT_PACK_METADATA,
 			  CSUM_HASH_IN_STREAM | CSUM_CLOSE |
 			  ((flags & WRITE_IDX_VERIFY) ? 0 : CSUM_FSYNC));
 
-	return rev_name;
+	return path;
 }
 
 static void write_mtimes_header(struct hashfile *f)
@@ -549,7 +553,7 @@ void stage_tmp_packfiles(struct strbuf *name_buffer,
 			 unsigned char hash[],
 			 char **idx_tmp_name)
 {
-	const char *rev_tmp_name = NULL;
+	char *rev_tmp_name = NULL;
 	char *mtimes_tmp_name = NULL;
 
 	if (adjust_shared_perm(pack_tmp_name))
@@ -575,7 +579,7 @@ void stage_tmp_packfiles(struct strbuf *name_buffer,
 	if (mtimes_tmp_name)
 		rename_tmp_packfile(name_buffer, mtimes_tmp_name, "mtimes");
 
-	free((char *)rev_tmp_name);
+	free(rev_tmp_name);
 	free(mtimes_tmp_name);
 }