Re: [PATCH 3/8] ublk: truncate io command result

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

On Mon, Mar 24, 2025 at 08:51:20AM -0700, Caleb Sander Mateos wrote:
> On Mon, Mar 24, 2025 at 6:49 AM Ming Lei <ming.lei@redhat.com> wrote:
> >
> > If io command result is bigger than request bytes, truncate it to request
> > bytes. This way is more reliable, and avoids potential risk, even though
> > both blk_update_request() and ublk_copy_user_pages() works fine in this
> > way.
> >
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> >  drivers/block/ublk_drv.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> > index 6fa1384c6436..acb6aed7be75 100644
> > --- a/drivers/block/ublk_drv.c
> > +++ b/drivers/block/ublk_drv.c
> > @@ -1071,6 +1071,10 @@ static inline void __ublk_complete_rq(struct request *req)
> >                 goto exit;
> >         }
> >
> > +       /* truncate result in case it is bigger than request bytes */
> > +       if (io->res > blk_rq_bytes(req))
> > +               io->res = blk_rq_bytes(req);
> 
> Is this not already handled by the code below that caps io->res?
> 
> unmapped_bytes = ublk_unmap_io(ubq, req, io);
> // ...
> if (unlikely(unmapped_bytes < io->res))
>         io->res = unmapped_bytes;
> 
> ublk_unmap_io() returns either blk_rq_bytes(req) or the result of
> ublk_copy_user_pages(), which should be at most blk_rq_bytes(req)?

Indeed, this patch can be dropped.


thanks,
Ming