Add documentation for user recovery feature of ublk subsystem. Signed-off-by: ZiyangZhang <ZiyangZhang@xxxxxxxxxxxxxxxxx> --- Documentation/block/ublk.rst | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/Documentation/block/ublk.rst b/Documentation/block/ublk.rst index 2122d1a4a541..c3dde087e601 100644 --- a/Documentation/block/ublk.rst +++ b/Documentation/block/ublk.rst @@ -144,6 +144,38 @@ managing and controlling ublk devices with help of several control commands: For retrieving device info via ``ublksrv_ctrl_dev_info``. It is the server's responsibility to save IO target specific info in userspace. +- ``UBLK_CMD_START_USER_RECOVERY`` + + This command is valid if ``UBLK_F_USER_RECOVERY`` feature is enabled. This + command is accepted after the old process has exited, ublk device is quiesced + and ``/dev/ublkc*`` is closed. User should send this command before he starts + a new process which opens ``/dev/ublkc*``. When this command returns, the + ublk device is ready for the new process. + +- ``UBLK_CMD_END_USER_RECOVERY`` + + This command is valid if ``UBLK_F_USER_RECOVERY`` feature is enabled. This + command is accepted after a new process has opened ``/dev/ublkc*`` and get + all ublk queues be ready. When this command returns, ublk device is + unquiesced and new I/O requests are passed to the new process. + +- user recovery feature description + + Two new features are added for user recovery: ``UBLK_F_USER_RECOVERY`` and + ``UBLK_F_USER_RECOVERY_REISSUE``. + + With ``UBLK_F_USER_RECOVERY`` set, after one ubq_daemon(ublksrv io handler) is + dying, ublk does not release ``/dev/ublkc*`` or ``/dev/ublkb*`` but requeues all + inflight requests which have not been issued to userspace. Requests which have + been issued to userspace are aborted. + + With ``UBLK_F_USER_RECOVERY_REISSUE`` set, after one ubq_daemon(ublksrv io + handler) is dying, contrary to ``UBLK_F_USER_RECOVERY``, requests which have been + issued to userspace are requeued and will be re-issued to the new process after + handling ``UBLK_CMD_END_USER_RECOVERY``. ``UBLK_F_USER_RECOVERY_REISSUE`` is + designed for backends who tolerate double-write since the driver may issue the + same I/O request twice. It might be useful to a read-only FS or a VM backend. + Data plane ---------- -- 2.27.0
