diff options
| -rw-r--r-- | fs/btrfs/volumes.c | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index be3fc701f389..a25d5bf4462f 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -197,6 +197,41 @@ static int __btrfs_map_block(struct btrfs_fs_info *fs_info, * device_list_mutex * chunk_mutex * balance_mutex + * + * + * Exclusive operations, BTRFS_FS_EXCL_OP + * ====================================== + * + * Maintains the exclusivity of the following operations that apply to the + * whole filesystem and cannot run in parallel. + * + * - Balance (*) + * - Device add + * - Device remove + * - Device replace (*) + * - Resize + * + * The device operations (as above) can be in one of the following states: + * + * - Running state + * - Paused state + * - Completed state + * + * Only device operations marked with (*) can go into the Paused state for the + * following reasons: + * + * - ioctl (only Balance can be Paused through ioctl) + * - filesystem remounted as read-only + * - filesystem unmounted and mounted as read-only + * - system power-cycle and filesystem mounted as read-only + * - filesystem or device errors leading to forced read-only + * + * BTRFS_FS_EXCL_OP flag is set and cleared using atomic operations. + * During the course of Paused state, the BTRFS_FS_EXCL_OP remains set. + * A device operation in Paused or Running state can be canceled or resumed + * either by ioctl (Balance only) or when remounted as read-write. + * BTRFS_FS_EXCL_OP flag is cleared when the device operation is canceled or + * completed. */ DEFINE_MUTEX(uuid_mutex); |