Re: [Qemu-devel] [PATCH] block: limited request size in write zeroes unsupported path

[Denis V. Lunev]

On 05/01/15 15:14, Peter Lieven wrote:
> On 05.01.2015 12:51, Denis V. Lunev wrote:
> > On 05/01/15 14:29, Peter Lieven wrote:
> > > If bs->bl.max_write_zeroes is large and we end up in the unsupported
> > > path we might allocate a lot of memory for the iovector and/or even
> > > generate an oversized requests.
> > >
> > > Fix this by limiting the request by the minimum of the reported
> > > maximum transfer size or 16MB (32768 sectors).
> > >
> > > Reported-by: Denis V. Lunev <address@hidden>
> > > Signed-off-by: Peter Lieven <address@hidden>
> > > ---
> > >   block.c |    5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/block.c b/block.c
> > > index a612594..8009478 100644
> > > --- a/block.c
> > > +++ b/block.c
> > > @@ -3203,6 +3203,9 @@ static int coroutine_fn 
> > > bdrv_co_do_write_zeroes(BlockDriverState *bs,
> > >
> > >           if (ret == -ENOTSUP) {
> > >               /* Fall back to bounce buffer if write zeroes is 
> > > unsupported */
> > > +            int max_xfer_len = 
> > > MIN_NON_ZERO(bs->bl.max_transfer_length,
> > > + MAX_WRITE_ZEROES_DEFAULT);
> > > +            num = MIN(num, max_xfer_len);
> > >               iov.iov_len = num * BDRV_SECTOR_SIZE;
> > >               if (iov.iov_base == NULL) {
> > >                   iov.iov_base = qemu_try_blockalign(bs, num * 
> > > BDRV_SECTOR_SIZE);
> > > @@ -3219,7 +3222,7 @@ static int coroutine_fn 
> > > bdrv_co_do_write_zeroes(BlockDriverState *bs,
> > >               /* Keep bounce buffer around if it is big enough for all
> > >                * all future requests.
> > >                */
> > > -            if (num < max_write_zeroes) {
> > > +            if (num < max_xfer_len) {
> > >                   qemu_vfree(iov.iov_base);
> > >                   iov.iov_base = NULL;
> > >               }
> > this is not going to work IMHO. num is the number in sectors.
> > max_xfer_len is in bytes.
>
> bs->bl.max_transfer_length is in sectors.
>
> Peter

oops. you are right...