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

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Message-ID: <Yy27b9CmdmNroIA5@T590>
Date:   Fri, 23 Sep 2022 21:58:07 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     ZiyangZhang <ZiyangZhang@...ux.alibaba.com>
Cc:     axboe@...nel.dk, xiaoguang.wang@...ux.alibaba.com,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        joseph.qi@...ux.alibaba.com
Subject: Re: [RESEND PATCH V5 7/7] Documentation: document ublk user recovery
 feature

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@...ux.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