[PATCH v4 10/11] refs/files: remove unused "errno == EISDIR" code

From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>, "Jeff King" <peff@peff.net>,
	"Han-Wen Nienhuys" <hanwen@google.com>,
	"Michael Haggerty" <mhagger@alum.mit.edu>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: [PATCH v4 10/11] refs/files: remove unused "errno == EISDIR" code
Date: Tue, 27 Jul 2021 01:44:26 +0200	[thread overview]
Message-ID: <patch-10.11-009abc9968-20210726T234237Z-avarab@gmail.com> (raw)
In-Reply-To: <cover-00.11-0000000000-20210726T234237Z-avarab@gmail.com>

When we lock a reference like "foo" we need to handle the case where
"foo" exists, but is an empty directory. That's what this code added
in bc7127ef0f (ref locking: allow 'foo' when 'foo/bar' used to exist
but not anymore., 2006-09-30) seems like it should be dealing with.

Except it doesn't, and we never take this branch. The reason is that
when bc7127ef0f was written this looked like:

	ref = resolve_ref([...]);
	if (!ref && errno == EISDIR) {
	[...]

And in resolve_ref() we had this code:

	fd = open(path, O_RDONLY);
	if (fd < 0)
		return NULL;

I.e. we would attempt to read "foo" with open(), which would fail with
EISDIR and we'd return NULL. We'd then take this branch, call
remove_empty_directories() and continue.

Since a1c1d8170d (refs_resolve_ref_unsafe: handle d/f conflicts for
writes, 2017-10-06) we don't. E.g. in the case of
files_copy_or_rename_ref() our callstack will look something like:

	[...] ->
	files_copy_or_rename_ref() ->
	lock_ref_oid_basic() ->
	refs_resolve_ref_unsafe()

At that point the first (now only) refs_resolve_ref_unsafe() call in
lock_ref_oid_basic() would do the equivalent of this in the resulting
call to refs_read_raw_ref() in refs_resolve_ref_unsafe():

	/* Via refs_read_raw_ref() */
	fd = open(path, O_RDONLY);
	if (fd < 0)
		/* get errno == EISDIR */
	/* later, in refs_resolve_ref_unsafe() */
	if ([...] && errno != EISDIR)
		return NULL;
	[...]
	/* returns the refs/heads/foo to the caller, even though it's a directory */
	return refname;

I.e. even though we got an "errno == EISDIR" we won't take this
branch, since in cases of EISDIR "resolved" is always
non-NULL. I.e. we pretend at this point as though everything's OK and
there is no "foo" directory.

We then proceed with the entire ref update and don't call
remove_empty_directories() until we call commit_ref_update(). See
5387c0d883 (commit_ref(): if there is an empty dir in the way, delete
it, 2016-05-05) for the addition of that code, and
a1c1d8170db (refs_resolve_ref_unsafe: handle d/f conflicts for writes,
2017-10-06) for the commit that changed the original codepath added in
bc7127ef0f to use this "EISDIR" handling.

Further historical commentary:

Before the two preceding commits the caller in files_reflog_expire()
was the only one out of our 4 callers that would pass non-NULL as an
oid. We would then set a (now gone) "resolve_flags" to
"RESOLVE_REF_READING" and just before that "errno != EISDIR" check do:

	if (resolve_flags & RESOLVE_REF_READING)
		return NULL;

There may have been some case where this ended up mattering and we
couldn't safely make this change before we removed the "oid"
parameter, but I don't think there was, see [1] for some discussion on
that.

In any case, now that we've removed the "oid" parameter in a preceding
commit we can be sure that this code is redundant, so let's remove it.

1. http://lore.kernel.org/git/871r801yp6.fsf@evledraar.gmail.com

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 refs/files-backend.c | 28 +++-------------------------
 1 file changed, 3 insertions(+), 25 deletions(-)

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 98d9aa1601..28cd8853f5 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -883,7 +883,6 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 	struct strbuf ref_file = STRBUF_INIT;
 	struct ref_lock *lock;
 	int last_errno = 0;
-	int resolved;
 
 	files_assert_main_repository(refs, "lock_ref_oid_basic");
 	assert(err);
@@ -891,30 +890,9 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 	CALLOC_ARRAY(lock, 1);
 
 	files_ref_path(refs, &ref_file, refname);
-	resolved = !!refs_resolve_ref_unsafe(&refs->base, refname,
-					     RESOLVE_REF_NO_RECURSE,
-					     &lock->old_oid, type);
-	if (!resolved && errno == EISDIR) {
-		/*
-		 * we are trying to lock foo but we used to
-		 * have foo/bar which now does not exist;
-		 * it is normal for the empty directory 'foo'
-		 * to remain.
-		 */
-		if (remove_empty_directories(&ref_file)) {
-			last_errno = errno;
-			if (!refs_verify_refname_available(
-					    &refs->base,
-					    refname, NULL, NULL, err))
-				strbuf_addf(err, "there are still refs under '%s'",
-					    refname);
-			goto error_return;
-		}
-		resolved = !!refs_resolve_ref_unsafe(&refs->base, refname,
-						     RESOLVE_REF_NO_RECURSE,
-						     &lock->old_oid, type);
-	}
-	if (!resolved) {
+	if (!refs_resolve_ref_unsafe(&refs->base, refname,
+				     RESOLVE_REF_NO_RECURSE,
+				     &lock->old_oid, type)) {
 		last_errno = errno;
 		if (last_errno != ENOTDIR ||
 		    !refs_verify_refname_available(&refs->base, refname,
-- 
2.32.0.956.g6b0c84ceda8

