[PATCH v3 3/8] packed-backend: check whether the "packed-refs" is regular file

[shejialuo <shejialuo@gmail.com>]

Although "git-fsck(1)" and "packed-backend.c" will check some
consistency and correctness of "packed-refs" file, they never check the
filetype of the "packed-refs". The user should always use "git
pack-refs" command to create the raw regular "packed-refs" file, so we
need to explicitly check this in "git refs verify".

We could use "open_nofollow" wrapper to open the raw "packed-refs" file.
If the returned "fd" value is less than 0, we could check whether the
"errno" is "ELOOP" to report an error to the user.

Reuse "FSCK_MSG_BAD_REF_FILETYPE" fsck message id to report the error to
the user if "packed-refs" is not a regular file.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: shejialuo <shejialuo@gmail.com>
---
 refs/packed-backend.c    | 39 +++++++++++++++++++++++++++++++++++----
 t/t0602-reffiles-fsck.sh | 22 ++++++++++++++++++++++
 2 files changed, 57 insertions(+), 4 deletions(-)

diff --git a/refs/packed-backend.c b/refs/packed-backend.c
index a7b6f74b6e..6401cecd5f 100644
--- a/refs/packed-backend.c
+++ b/refs/packed-backend.c
@@ -4,6 +4,7 @@
 #include "../git-compat-util.h"
 #include "../config.h"
 #include "../dir.h"
+#include "../fsck.h"
 #include "../gettext.h"
 #include "../hash.h"
 #include "../hex.h"
@@ -1748,15 +1749,45 @@ static struct ref_iterator *packed_reflog_iterator_begin(struct ref_store *ref_s
 	return empty_ref_iterator_begin();
 }
 
-static int packed_fsck(struct ref_store *ref_store UNUSED,
-		       struct fsck_options *o UNUSED,
+static int packed_fsck(struct ref_store *ref_store,
+		       struct fsck_options *o,
 		       struct worktree *wt)
 {
+	struct packed_ref_store *refs = packed_downcast(ref_store,
+							REF_STORE_READ, "fsck");
+	int ret = 0;
+	int fd;
 
 	if (!is_main_worktree(wt))
-		return 0;
+		goto cleanup;
 
-	return 0;
+	if (o->verbose)
+		fprintf_ln(stderr, "Checking packed-refs file %s", refs->path);
+
+	fd = open_nofollow(refs->path, O_RDONLY);
+	if (fd < 0) {
+		/*
+		 * If the packed-refs file doesn't exist, there's nothing
+		 * to check.
+		 */
+		if (errno == ENOENT)
+			goto cleanup;
+
+		if (errno == ELOOP) {
+			struct fsck_ref_report report = { 0 };
+			report.path = "packed-refs";
+			ret = fsck_report_ref(o, &report,
+					      FSCK_MSG_BAD_REF_FILETYPE,
+					      "not a regular file");
+			goto cleanup;
+		}
+
+		ret = error_errno(_("unable to open %s"), refs->path);
+		goto cleanup;
+	}
+
+cleanup:
+	return ret;
 }
 
 struct ref_storage_be refs_be_packed = {
diff --git a/t/t0602-reffiles-fsck.sh b/t/t0602-reffiles-fsck.sh
index cf7a202d0d..42c8d4ca1e 100755
--- a/t/t0602-reffiles-fsck.sh
+++ b/t/t0602-reffiles-fsck.sh
@@ -617,4 +617,26 @@ test_expect_success 'ref content checks should work with worktrees' '
 	)
 '
 
+test_expect_success SYMLINKS 'the filetype of packed-refs should be checked' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit default &&
+		git branch branch-1 &&
+		git branch branch-2 &&
+		git branch branch-3 &&
+		git pack-refs --all &&
+
+		mv .git/packed-refs .git/packed-refs-back &&
+		ln -sf packed-refs-bak .git/packed-refs &&
+		test_must_fail git refs verify 2>err &&
+		cat >expect <<-EOF &&
+		error: packed-refs: badRefFiletype: not a regular file
+		EOF
+		rm .git/packed-refs &&
+		test_cmp expect err
+	)
+'
+
 test_done
-- 
2.48.1