packed_refs_lock(): report errors via a `struct strbuf *err`

That way the callers don't have to come up with error messages
themselves.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/files-backend.c

@@ -1096,7 +1096,7 @@ static int files_pack_refs(struct ref_store *ref_store, unsigned int flags)
 	struct ref_to_prune *refs_to_prune = NULL;
 	struct strbuf err = STRBUF_INIT;
 
-	packed_refs_lock(refs->packed_ref_store, LOCK_DIE_ON_ERROR);
+	packed_refs_lock(refs->packed_ref_store, LOCK_DIE_ON_ERROR, &err);
 
 	iter = cache_ref_iterator_begin(get_loose_ref_cache(refs), NULL, 0);
 	while ((ok = ref_iterator_advance(iter)) == ITER_OK) {
@@ -2679,9 +2679,7 @@ static int files_initial_transaction_commit(struct ref_store *ref_store,
 		}
 	}
 
-	if (packed_refs_lock(refs->packed_ref_store, 0)) {
-		strbuf_addf(err, "unable to lock packed-refs file: %s",
-			    strerror(errno));
+	if (packed_refs_lock(refs->packed_ref_store, 0, err)) {
 		ret = TRANSACTION_GENERIC_ERROR;
 		goto cleanup;
 	}

refs/packed-backend.c

@@ -515,7 +515,7 @@ static int write_packed_entry(FILE *fh, const char *refname,
 	return 0;
 }
 
-int packed_refs_lock(struct ref_store *ref_store, int flags)
+int packed_refs_lock(struct ref_store *ref_store, int flags, struct strbuf *err)
 {
 	struct packed_ref_store *refs =
 		packed_downcast(ref_store, REF_STORE_WRITE | REF_STORE_MAIN,
@@ -537,9 +537,15 @@ int packed_refs_lock(struct ref_store *ref_store, int flags)
 	if (hold_lock_file_for_update_timeout(
 			    &refs->lock,
 			    refs->path,
-			    flags, timeout_value) < 0 ||
-	    close_lock_file(&refs->lock))
+			    flags, timeout_value) < 0) {
+		unable_to_lock_message(refs->path, errno, err);
 		return -1;
+	}
+
+	if (close_lock_file(&refs->lock)) {
+		strbuf_addf(err, "unable to close %s: %s", refs->path, strerror(errno));
+		return -1;
+	}
 
 	/*
 	 * Now that we hold the `packed-refs` lock, make sure that our
@@ -698,10 +704,9 @@ int repack_without_refs(struct ref_store *ref_store,
 	if (!needs_repacking)
 		return 0; /* no refname exists in packed refs */
 
-	if (packed_refs_lock(&refs->base, 0)) {
-		unable_to_lock_message(refs->path, errno, err);
+	if (packed_refs_lock(&refs->base, 0, err))
 		return -1;
-	}
+
 	packed = get_packed_refs(refs);
 
 	/* Remove refnames from the cache */

refs/packed-backend.h

@@ -6,10 +6,10 @@ struct ref_store *packed_ref_store_create(const char *path,
 
 /*
  * Lock the packed-refs file for writing. Flags is passed to
- * hold_lock_file_for_update(). Return 0 on success. On errors, set
- * errno appropriately and return a nonzero value.
+ * hold_lock_file_for_update(). Return 0 on success. On errors, write
+ * an error message to `err` and return a nonzero value.
  */
-int packed_refs_lock(struct ref_store *ref_store, int flags);
+int packed_refs_lock(struct ref_store *ref_store, int flags, struct strbuf *err);
 
 void add_packed_ref(struct ref_store *ref_store,
 		    const char *refname, const struct object_id *oid);