Subject: Re: [PATCH v5 2/6] refs/files-backend: stop setting errno from lock_ref_oid_basic

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Sun, 11 Jul 2021 13:38:48 +0200

On Wed, Jul 07 2021, Han-Wen Nienhuys via GitGitGadget wrote:

>  /*
>   * Locks a ref returning the lock on success and NULL on failure.
> - * On failure errno is set to something meaningful.
>   */
>  static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
>  					   const char *refname,
> @@ -922,7 +921,6 @@ 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 mustexist = (old_oid && !is_null_oid(old_oid));
>  	int resolve_flags = RESOLVE_REF_NO_RECURSE;
>  	int resolved;
> @@ -949,7 +947,6 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
>  		 * to remain.
>  		 */
>  		if (remove_empty_directories(&ref_file)) {
> -			last_errno = errno;
>  			if (!refs_verify_refname_available(
>  					    &refs->base,
>  					    refname, extras, skip, err))
> @@ -962,10 +959,13 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
>  						     &lock->old_oid, type);
>  	}
>  	if (!resolved) {
> -		last_errno = errno;
> +		int last_errno = errno;
>  		if (last_errno != ENOTDIR ||
> -		    !refs_verify_refname_available(&refs->base, refname,
> -						   extras, skip, err))
> +		    /* in case of D/F conflict, try to generate a better error
> +		     * message. If that fails, fall back to strerror(ENOTDIR).
> +		     */
> +		    !refs_verify_refname_available(&refs->base, refname, extras,
> +						   skip, err))
>  			strbuf_addf(err, "unable to resolve reference '%s': %s",
>  				    refname, strerror(last_errno));

I don't think it's some dealbreaker and we can move on, but just FWIW I
think what I mentioned ending in your
https://lore.kernel.org/git/CAFQ2z_NpyJQLuM70MhJ8K1h2v3QXFuAZRjN=[email-masked]/
is still outstanding.

I.e. you added the comment, which is just says what the error emitting
looks like, that's all well & good.

But what I was pointing out that it didn't make sense to do any
"last_errno" here at all anymore. You pointed to 5b2d8d6f218
(lock_ref_sha1_basic(): improve diagnostics for ref D/F conflicts,
2015-05-11), we started setting "last_errno" there, but that was *not*
to avoid clobbering between the !resolved and the
strbuf_add(strerror(last_errno)) here, but rather to carry the
"last_errno" forward to the end of this lock_ref_oid_basic(), because
other things (after this hunk) might reset/clear errno.

Anyway, as noted there it doesn't actually matter, just reviewing &
looking if there's any loose ends, and for future source spelunking for
anyone reading this thread.

I.e. something like what I mentioned in
https://lore.kernel.org/git/[email-masked]/ could be
squashed in, or better yet (probably) this:

diff --git a/refs/files-backend.c b/refs/files-backend.c
index 83ddfb3b627..f0ce0aac857 100644
--- a/refs/files-backend.c
+++ b/refs/files-backend.c
@@ -958,17 +958,15 @@ static struct ref_lock *lock_ref_oid_basic(struct files_ref_store *refs,
 						     refname, resolve_flags,
 						     &lock->old_oid, type);
 	}
-	if (!resolved) {
-		int last_errno = errno;
-		if (last_errno != ENOTDIR ||
-		    /* in case of D/F conflict, try to generate a better error
-		     * message. If that fails, fall back to strerror(ENOTDIR).
-		     */
-		    !refs_verify_refname_available(&refs->base, refname, extras,
-						   skip, err))
-			strbuf_addf(err, "unable to resolve reference '%s': %s",
-				    refname, strerror(last_errno));
-
+	if (!resolved &&
+	    (errno != ENOTDIR ||
+	     /* in case of D/F conflict, try to generate a better error
+	      * message. If that fails, fall back to strerror(ENOTDIR).
+	      */
+	     !refs_verify_refname_available(&refs->base, refname, extras,
+					    skip, err))) {
+		strbuf_addf(err, "unable to resolve reference '%s': %s",
+			    refname, strerror(errno));
 		goto error_return;
 	}