btrfs: add_missing_dev() should return the actual error

add_missing_dev() can return device pointer so that IS_ERR/PTR_ERR can
be used to check for the actual error that occurred in the function.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
[ minor error message adjustment ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -6238,7 +6238,7 @@ static struct btrfs_device *add_missing_dev(struct btrfs_fs_devices *fs_devices,
 
 	device = btrfs_alloc_device(NULL, &devid, dev_uuid);
 	if (IS_ERR(device))
-		return NULL;
+		return device;
 
 	list_add(&device->dev_list, &fs_devices->devices);
 	device->fs_devices = fs_devices;
@@ -6443,9 +6443,12 @@ static int read_one_chunk(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
 			map->stripes[i].dev =
 				add_missing_dev(fs_info->fs_devices, devid,
 						uuid);
-			if (!map->stripes[i].dev) {
+			if (IS_ERR(map->stripes[i].dev)) {
 				free_extent_map(em);
-				return -EIO;
+				btrfs_err(fs_info,
+					"failed to init missing dev %llu: %ld",
+					devid, PTR_ERR(map->stripes[i].dev));
+				return PTR_ERR(map->stripes[i].dev);
 			}
 			btrfs_report_missing_device(fs_info, devid, uuid);
 		}
@@ -6571,8 +6574,12 @@ static int read_one_dev(struct btrfs_fs_info *fs_info,
 		}
 
 		device = add_missing_dev(fs_devices, devid, dev_uuid);
-		if (!device)
-			return -ENOMEM;
+		if (IS_ERR(device)) {
+			btrfs_err(fs_info,
+				"failed to add missing dev %llu: %ld",
+				devid, PTR_ERR(device));
+			return PTR_ERR(device);
+		}
 		btrfs_report_missing_device(fs_info, devid, dev_uuid);
 	} else {
 		if (!device->bdev) {