refdb: don't report failure for expected errors

There might be a few threads or processes working with references
concurrently, so fortify the code to ignore errors which come from
concurrent access which do not stop us from continuing the work.

This includes ignoring an unlinking error. Either someone else removed
it or we leave the file around. In the former case the job is done, and
in the latter case, the ref is still in a valid state.

src/refdb_fs.c

@@ -902,7 +902,7 @@ static int packed_remove_loose(refdb_fs_backend *backend)
 {
 	size_t i;
 	git_buf ref_content = GIT_BUF_INIT;
-	int failed = 0, error = 0;
+	int error = 0;
 
 	/* backend->refcache is already locked when this is called */
 
@@ -917,12 +917,12 @@ static int packed_remove_loose(refdb_fs_backend *backend)
 		/* We need to stop anybody from updating the ref while we try to do a safe delete */
 		error = loose_lock(&lock, backend, ref->name);
 		/* If someone else is updating it, let them do it */
-		if (error == GIT_EEXISTS)
+		if (error == GIT_EEXISTS || error == GIT_ENOTFOUND)
 			continue;
 
 		if (error < 0) {
-			failed = 1;
-			continue;
+			giterr_set(GITERR_REFERENCE, "failed to lock loose reference '%s'", ref->name);
+			return error;
 		}
 
 		error = git_futils_readbuffer(&ref_content, lock.path_original);
@@ -940,7 +940,6 @@ static int packed_remove_loose(refdb_fs_backend *backend)
 
 		/* Figure out the current id; if we fail record it but don't fail the whole operation */
 		if ((error = loose_parse_oid(&current_id, lock.path_original, &ref_content)) < 0) {
-			failed = 1;
 			git_filebuf_cleanup(&lock);
 			continue;
 		}
@@ -951,27 +950,17 @@ static int packed_remove_loose(refdb_fs_backend *backend)
 			continue;
 		}
 
-		if (p_unlink(lock.path_original) < 0) {
-			if (failed)
-				continue;
-
-			giterr_set(GITERR_REFERENCE,
-				"Failed to remove loose reference '%s' after packing: %s",
-				lock.path_original, strerror(errno));
-			failed = 1;
-		}
-
-		git_filebuf_cleanup(&lock);
-
 		/*
 		 * if we fail to remove a single file, this is *not* good,
 		 * but we should keep going and remove as many as possible.
-		 * After we've removed as many files as possible, we return
-		 * the error code anyway.
+		 * If we fail to remove, the ref is still in the old state, so
+		 * we haven't lost information.
 		 */
+		p_unlink(lock.path_original);
+		git_filebuf_cleanup(&lock);
 	}
 
-	return failed ? -1 : 0;
+	return 0;
 }
 
 /*