Re: [RESEND PATCH V5 7/7] Documentation: document ublk user recovery feature

Ming Lei
2022-09-23T13:58:41Z

On Fri, Sep 23, 2022 at 02:15:05PM +0800, ZiyangZhang wrote:
> Add documentation for user recovery feature of ublk subsystem.
>
> Signed-off-by: ZiyangZhang <ZiyangZhang@linux.alibaba.com>
> ---
> 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

The above looks not accurate, the old ubq daemon has to release
/dev/ublkc*, and the new ubq daemon needs to re-open it, and
here I think it is fine to just mention /dev/ublkb* won't be
deleted during the whole recovery, or the device ID is kept,
and it is ublk server's responsibility to recover the device
context by its own knowledge.

thanks,
Ming