Re: [Qemu-devel] [PATCH 08/17] add unix_msgfd_lookup() to callback get_buffer

[Lei Li]

On 11/26/2013 07:31 PM, Paolo Bonzini wrote:
> Il 21/11/2013 10:11, Lei Li ha scritto:
> > +            /*
> > +             * recvmsg is called here to catch the control message for
> > +             * the exchange of PIPE file descriptor until it is received.
> > +             */
> > +            len = recvmsg(s->sockfd, &msg, 0);
> > +            if (len != -1) {
> > +                if (unix_msgfd_lookup(s, &msg) > 0) {
> > +                    pipefd_passed = 1;
> > +                    /*
> > +                     * Do not count one byte taken by the PIPE file
> > +                     * descriptor.
> > +                     */
> > +                    len--;
> I think adding a byte in the middle of the stream is not reliable.
>
> Rather, you should transmit the socket always at the same place, for
> example in the first call of qemu_local_save_ram, after it has written
> the 64-bit field.

I guess 'transmit the socket' you mean transmit the fd?

Sorry that I am quite understand your suggestion here.. Do you
mean that send_pipefd in the first call of qemu_local_save_ram
after it has written the 64-bit field? In this way, get rid of
qemu_local_send_pipefd?

Currently, the fd control message is sent at the end of the stream
in ram_save_setup stage, followed by the ram page. The control
message of fd is always at the same place.

> The matching code in qemu_local_ram_load will be like this:
>
> static int qemu_local_ram_load(QEMUFile *f, void *opaque,
>                                 uint64_t flags)
> {
>      QEMUFileLocal *s = opaque;
>      ram_addr_t addr;
>      struct iovec iov;
>      ssize_t ret = -EINVAL;
>
>      if (!s->pipefd_received) {
>          /*
>           * send_pipefd was called at this point, and it wrote one byte
>           * to the stream.
>           */
>          qemu_get_byte(s);
>          s->pipefd_received = true;
>      }
>
>      if (pipefd_passed) {
>          ...
>      }
>      return -EINVAL;
> }
>
> Also, please move pipefd_passed within QEMUFileLocal.
>
> Thanks,
>
> Paolo


--
Lei