Re: [PATCH v4 2/2] migration: check magic value for deciding the mapping of channels

[manish.mishra]

On 23/11/22 9:57 pm, Peter Xu wrote:
> On Wed, Nov 23, 2022 at 09:28:14PM +0530, manish.mishra wrote:
> > On 23/11/22 9:22 pm, Peter Xu wrote:
> > > On Wed, Nov 23, 2022 at 03:05:27PM +0000, manish.mishra wrote:
> > > > +int migration_channel_read_peek(QIOChannel *ioc,
> > > > +                                const char *buf,
> > > > +                                const size_t buflen,
> > > > +                                Error **errp)
> > > > +{
> > > > +   ssize_t len = 0;
> > > > +   struct iovec iov = { .iov_base = (char *)buf, .iov_len = buflen };
> > > > +
> > > > +   while (len < buflen) {
> > > > +       len = qio_channel_readv_full(ioc, &iov, 1, NULL,
> > > > +                                    NULL, QIO_CHANNEL_READ_FLAG_MSG_PEEK, 
> > > > errp);
> > > > +
> > > > +       if (len == QIO_CHANNEL_ERR_BLOCK) {
> > > This needs to take care of partial len too?
> >
> > sorry Peter, I did not quite understand it. Can you please give some more 
> > details.
> As Daniel pointed out, I think if we peek partially it'll go into a loop.
> Since we shouldn't read 0 anyway here, maybe you can directly write it as:
>
> while (true) {
>    len = read();
>    if (len <= 0 && len != QIO_CHANNEL_ERR_BLOCK) {
>        error_setg(...);
>        return -1;
>    }
>    if (len == buflen) {
>        break;
>    }
>    /* For either partial peek or QIO_CHANNEL_ERR_BLOCK, retry with timeout */
>    sleep();
> }


Yes, got it, sorry, will update it.

Thanks

Manish Mishra

> > > > +            if (qemu_in_coroutine()) {
> > > > +                /* 1ms sleep. */
> > > > +                qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, 1000000);
> > > > +            } else {
> > > > +                qio_channel_wait(ioc, G_IO_IN);
> > > > +            }
> > > > +            continue;
> > > > +       }
> > > > +       if (len == 0) {
> > > > +           error_setg(errp,
> > > > +                      "Unexpected end-of-file on channel");
> > > > +           return -1;
> > > > +       }
> > > > +       if (len < 0) {
> > > > +           return -1;
> > > > +       }
> > > > +   }
> > > > +
> > > > +   return 0;
> > > > +}
> > Thanks
> >
> > Manish Mishra