On Wed, Jun 08, 2022 at 07:46:43PM +0100, Daniel P. Berrangé wrote:
> On Wed, Jun 08, 2022 at 03:18:09PM -0300, Leonardo Bras wrote:
> > Somewhere between v6 and v7 the of the zero-copy-send patchset a crucial
> > part of the flushing mechanism got missing: incrementing zero_copy_queued.
> >
> > Without that, the flushing interface becomes a no-op, and there is no
> > garantee the buffer is really sent.
> >
> > This can go as bad as causing a corruption in RAM during migration.
> >
> > Fixes: 2bc58ffc2926 ("QIOChannelSocket: Implement io_writev zero copy flag
> > & io_flush for CONFIG_LINUX")
> > Reported-by: 徐闯 <xuchuangxc...@bytedance.com>
> > Signed-off-by: Leonardo Bras <leob...@redhat.com>
> > ---
> > io/channel-socket.c | 11 ++++++++---
> > 1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/io/channel-socket.c b/io/channel-socket.c
> > index dc9c165de1..ca4cae930f 100644
> > --- a/io/channel-socket.c
> > +++ b/io/channel-socket.c
> > @@ -554,6 +554,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel
> > *ioc,
> > size_t fdsize = sizeof(int) * nfds;
> > struct cmsghdr *cmsg;
> > int sflags = 0;
> > + bool zero_copy_enabled = false;
> >
> > memset(control, 0, CMSG_SPACE(sizeof(int) * SOCKET_MAX_FDS));
> >
> > @@ -581,6 +582,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel
> > *ioc,
> > #ifdef QEMU_MSG_ZEROCOPY
> > if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
> > sflags = MSG_ZEROCOPY;
> > + zero_copy_enabled = true;
> > }
> > #endif
> >
> > @@ -592,21 +594,24 @@ static ssize_t qio_channel_socket_writev(QIOChannel
> > *ioc,
> > return QIO_CHANNEL_ERR_BLOCK;
> > case EINTR:
> > goto retry;
> > -#ifdef QEMU_MSG_ZEROCOPY
>
> Removing this ifdef appears incidental to the change. If this is
> redundant just remove it in its own patch.
>
> > case ENOBUFS:
> > - if (sflags & MSG_ZEROCOPY) {
> > + if (zero_copy_enabled) {
> > error_setg_errno(errp, errno,
> > "Process can't lock enough memory for
> > using MSG_ZEROCOPY");
> > return -1;
> > }
> > break;
> > -#endif
> > }
> >
> > error_setg_errno(errp, errno,
> > "Unable to write to socket");
> > return -1;
> > }
> > +
> > + if (zero_copy_enabled) {
>
> What's wrong with
>
> if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
> sioc->zero_copy_queued++;
> }
>
>
> Introducing another local variable doesn't really add value IMHO.
One benefit of having that variable is we setup zero_copy_enabled once in
the #ifdef and the rest code can avoid wrapping with the macro. From that
pov the patch looks okay to me. Thanks,
--
Peter Xu
