Re: [Qemu-block] [Qemu-devel] [PATCH 2/2] block/nfs: try to avoid the bounce buffer in pwritev

[Jeff Cody]

On Fri, Feb 17, 2017 at 03:42:52PM -0600, Eric Blake wrote:
> On 02/17/2017 03:37 PM, Jeff Cody wrote:
> > On Fri, Feb 17, 2017 at 05:39:01PM +0100, Peter Lieven wrote:
> >> if the passed qiov contains exactly one iov we can
> >> pass the buffer directly.
> >>
> >> Signed-off-by: Peter Lieven <address@hidden>
> >> ---
> >>  block/nfs.c | 23 ++++++++++++++++-------
> >>  1 file changed, 16 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/block/nfs.c b/block/nfs.c
> >> index ab5dcc2..bb4b75f 100644
> >> --- a/block/nfs.c
> >> +++ b/block/nfs.c
> >> @@ -295,20 +295,27 @@ static int coroutine_fn 
> >> nfs_co_pwritev(BlockDriverState *bs, uint64_t offset,
> >>      NFSClient *client = bs->opaque;
> >>      NFSRPC task;
> >>      char *buf = NULL;
> >> +    bool my_buffer = false;
> > 
> > g_free() is a nop if buf is NULL, so there is no need for the my_buffer
> > variable & check.
> 
> Umm, yes there is:
> 
> >> +    if (iov->niov != 1) {
> >> +        buf = g_try_malloc(bytes);
> >> +        if (bytes && buf == NULL) {
> >> +            return -ENOMEM;
> >> +        }
> >> +        qemu_iovec_to_buf(iov, 0, buf, bytes);
> >> +        my_buffer = true;
> >> +    } else {
> >> +        buf = iov->iov[0].iov_base;
> 
> If we took the else branch, then we definitely do not want to be calling
> g_free(buf).

Doh!

> 
> >>      }
> >>  
> >> -    qemu_iovec_to_buf(iov, 0, buf, bytes);
> >> -
> >>      if (nfs_pwrite_async(client->context, client->fh,
> >>                           offset, bytes, buf,
> >>                           nfs_co_generic_cb, &task) != 0) {
> >> -        g_free(buf);
> >> +        if (my_buffer) {
> >> +            g_free(buf);
> >> +        }
> 
> It looks correct as-is to me.

Indeed.

Reviewed-by: Jeff Cody <address@hidden>