Re: [virtio-dev] Re: [PATCH v3 3/6] vhost-user: support receiving file descriptors in slave_read

[Tiwei Bie <tiwei.bie@intel.com>]

On Thu, May 24, 2018 at 12:25:23AM +0300, Michael S. Tsirkin wrote:
> On Thu, Apr 12, 2018 at 11:12:29PM +0800, Tiwei Bie wrote:
> > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> 
> 
> Thinking about it, I think we should add a protocol
> feature for this. This way remote can find out whether
> it's safe to send this data to us.

Okay, I can add a protocol feature for this.
Do you think it's OK to keep this patch as is
(this patch just extends slave_read() to support
receiving file descriptors) and introduce the
new protocol feature in a new patch to allow
backends to send file descriptors?

Best regards,
Tiwei Bie

> 
> > ---
> >  hw/virtio/vhost-user.c | 41 ++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 40 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > index 91edd95453..9cea2c8c51 100644
> > --- a/hw/virtio/vhost-user.c
> > +++ b/hw/virtio/vhost-user.c
> > @@ -854,14 +854,44 @@ static void slave_read(void *opaque)
> >      VhostUserHeader hdr = { 0, };
> >      VhostUserPayload payload = { 0, };
> >      int size, ret = 0;
> > +    struct iovec iov;
> > +    struct msghdr msgh;
> > +    int fd = -1;
> > +    char control[CMSG_SPACE(sizeof(fd))];
> > +    struct cmsghdr *cmsg;
> > +    size_t fdsize;
> > +
> > +    memset(&msgh, 0, sizeof(msgh));
> > +    msgh.msg_iov = &iov;
> > +    msgh.msg_iovlen = 1;
> > +    msgh.msg_control = control;
> > +    msgh.msg_controllen = sizeof(control);
> >  
> >      /* Read header */
> > -    size = read(u->slave_fd, &hdr, VHOST_USER_HDR_SIZE);
> > +    iov.iov_base = &hdr;
> > +    iov.iov_len = VHOST_USER_HDR_SIZE;
> > +
> > +    size = recvmsg(u->slave_fd, &msgh, 0);
> >      if (size != VHOST_USER_HDR_SIZE) {
> >          error_report("Failed to read from slave.");
> >          goto err;
> >      }
> >  
> > +    if (msgh.msg_flags & MSG_CTRUNC) {
> > +        error_report("Truncated message.");
> > +        goto err;
> > +    }
> > +
> > +    for (cmsg = CMSG_FIRSTHDR(&msgh); cmsg != NULL;
> > +         cmsg = CMSG_NXTHDR(&msgh, cmsg)) {
> > +            if (cmsg->cmsg_level == SOL_SOCKET &&
> > +                cmsg->cmsg_type == SCM_RIGHTS) {
> > +                    fdsize = cmsg->cmsg_len - CMSG_LEN(0);
> > +                    memcpy(&fd, CMSG_DATA(cmsg), fdsize);
> > +                    break;
> > +            }
> > +    }
> > +
> >      if (hdr.size > VHOST_USER_PAYLOAD_SIZE) {
> >          error_report("Failed to read msg header."
> >                  " Size %d exceeds the maximum %zu.", hdr.size,
> > @@ -885,9 +915,15 @@ static void slave_read(void *opaque)
> >          break;
> >      default:
> >          error_report("Received unexpected msg type.");
> > +        if (fd != -1) {
> > +            close(fd);
> > +        }
> >          ret = -EINVAL;
> >      }
> >  
> > +    /* Message handlers need to make sure that fd will be consumed. */
> > +    fd = -1;
> > +
> >      /*
> >       * REPLY_ACK feature handling. Other reply types has to be managed
> >       * directly in their request handlers.
> > @@ -920,6 +956,9 @@ err:
> >      qemu_set_fd_handler(u->slave_fd, NULL, NULL, NULL);
> >      close(u->slave_fd);
> >      u->slave_fd = -1;
> > +    if (fd != -1) {
> > +        close(fd);
> > +    }
> >      return;
> >  }
> >  
> > -- 
> > 2.11.0
> 
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