Re: [PATCH] ublk: Add UBLK_U_CMD_SET_SIZE

[Ming Lei <ming.lei@redhat.com>]

On Mon, Apr 07, 2025 at 11:14:34AM +0800, Ming Lei wrote:
> On Sun, Apr 06, 2025 at 11:17:05PM +0300, Jared Holzman wrote:
> > Hi Ming,
> > 
> > On 05/04/2025 5:51, Ming Lei wrote:
> > > External email: Use caution opening links or attachments
> > > 
> > > 
> > > Hello Jared,
> > > 
> > > On Thu, Apr 03, 2025 at 12:37:11PM +0000, Jared Holzman wrote:
> > > > Apologies if this is a dup, but I am not seeing the original mail on the mailing list archive.
> > > I guess it is because the patch is sent as html, instead of plain test,
> > > please follow the patch submission guide:
> > > 
> > > https://www.kernel.org/doc/Documentation/process/submitting-patches.rst
> > 
> > Sorry about that, I originally sent the mail using git send-mail, but our
> > internal smtp relay does not support outside addresses. I then tried
> > forwarding it from Outlook and it decided to add HTML without telling me.
> > 
> > I'm using Thunderbird now, so hopefully it will be in plain-text as
> > required.
> > 
> > > > ________________________________
> > > > From: Jared Holzman <jholzman@nvidia.com>
> > > > Sent: Monday, 31 March 2025 4:54 PM
> > > > To: linux-block@vger.kernel.org <linux-block@vger.kernel.org>
> > > > Cc: ming.lei@redhat.com <ming.lei@redhat.com>; Omri Mann <omri@nvidia.com>; Ofer Oshri <ofer@nvidia.com>; Omri Levi <omril@nvidia.com>; Jared Holzman <jholzman@nvidia.com>
> > > > Subject: [PATCH] ublk: Add UBLK_U_CMD_SET_SIZE
> > > > 
> > > > From: Omri Mann <omri@nvidia.com>
> > > > 
> > > > Currently ublk only allows the size of the ublkb block device to be
> > > > set via UBLK_CMD_SET_PARAMS before UBLK_CMD_START_DEV is triggered.
> > > > 
> > > > This does not provide support for extendable user-space block devices
> > > > without having to stop and restart the underlying ublkb block device
> > > > causing IO interruption.
> > > The requirement is reasonable.
> > > 
> > > > This patch adds a new ublk command UBLK_U_CMD_SET_SIZE to allow the
> > > > ublk block device to be resized on-the-fly.
> > > Looks CMD_SET_SIZE is not generic enough, maybe UBLK_CMD_UPDATE_PARAMS
> > > can be added for support any parameter update by allowing to do it
> > > when device is in LIVE state.
> > 
> > That's fine, but we'd rather not take on the burden of verifying all of
> > ublk_params to see which ones can be safely changed on-the-fly.
> > 
> > Would it be reasonable to have UBLK_CMD_UPDATE_PARAMS accept a different
> > struct "ublk_param_update" which contains only the parameters that can be
> > updated in the LIVE state and will include only max_sectors for now?
> > 
> > Alternatively if you know off the top of your head which parameters can be
> > easily changed on-the-fly and we will add only those.
>  
> Fair enough, updating 'dev_sectors' should be generic enough, and it looks
> fine to add UBLK_U_CMD_SET_SIZE.

Also UBLK_U_CMD_SET_SIZE may be renamed as UBLK_U_CMD_UPDATE_SIZE.


Thanks,
Ming