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| author |   ZiyangZhang <ZiyangZhang@linux.alibaba.com> | 2022-10-18 12:53:46 +0800 |
|---|---|---|
| committer |   Jens Axboe <axboe@kernel.dk> | 2022-10-18 05:12:26 -0700 |
| commit | e0539ae012ba5d618eb19665ff990b87b960c643 (patch) | |
| tree | 89d77e0889e79b39c98756c72d254e37e14457db /Documentation | |
| parent | blk-mq: fix null pointer dereference in blk_mq_clear_rq_mapping() (diff) | |
| download | linux-dev-e0539ae012ba5d618eb19665ff990b87b960c643.tar.xz linux-dev-e0539ae012ba5d618eb19665ff990b87b960c643.zip | |
Documentation: document ublk user recovery feature
Add documentation for user recovery feature of ublk subsystem.
Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20221018045346.99706-2-ZiyangZhang@linux.alibaba.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/block/ublk.rst | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/Documentation/block/ublk.rst b/Documentation/block/ublk.rst index 2122d1a4a541..ba45c46cc0da 100644 --- a/Documentation/block/ublk.rst +++ b/Documentation/block/ublk.rst @@ -144,6 +144,42 @@ 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 released. User should send this command before he starts + a new process which re-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 ublk device is quiesced and 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(ublk server's io + handler) is dying, ublk does not delete ``/dev/ublkb*`` during the whole + recovery stage and ublk device ID is kept. It is ublk server's + responsibility to recover the device context by its own knowledge. + Requests which have not been issued to userspace are requeued. Requests + which have been issued to userspace are aborted. + + With ``UBLK_F_USER_RECOVERY_REISSUE`` set, after one ubq_daemon(ublk + server's 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 ---------- |