Re: [Qemu-devel] [PATCH v7 11/42] Return path: socket_writev_buffer: Block even on non-blocking fd's

[Juan Quintela]

"Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> The destination sets the fd to non-blocking on incoming migrations;
> this also affects the return path from the destination, and thus we
> need to make sure we can safely write to the return path.
>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>

Reviewed-by: Juan Quintela <address@hidden>


>  migration/qemu-file-unix.c | 41 ++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 36 insertions(+), 5 deletions(-)
>
> diff --git a/migration/qemu-file-unix.c b/migration/qemu-file-unix.c
> index 561621e..b6c55ab 100644
> --- a/migration/qemu-file-unix.c
> +++ b/migration/qemu-file-unix.c
> @@ -39,12 +39,43 @@ static ssize_t socket_writev_buffer(void *opaque, struct 
> iovec *iov, int iovcnt,
>      QEMUFileSocket *s = opaque;
>      ssize_t len;
>      ssize_t size = iov_size(iov, iovcnt);
> +    ssize_t offset = 0;
> +    int     err;
>  
> -    len = iov_send(s->fd, iov, iovcnt, 0, size);
> -    if (len < size) {
> -        len = -socket_error();
> -    }
> -    return len;
> +    while (size > 0) {
> +        len = iov_send(s->fd, iov, iovcnt, offset, size);
> +
> +        if (len > 0) {
> +            size -= len;
> +            offset += len;
> +        }

ion_send() can return -1 on error

This looks a "hacky way" to look for it, althoght my understanding is
that it is correct, so the review-by


> +
> +        if (size > 0) {
> +            err = socket_error();
> +
> +            if (err != EAGAIN && err != EWOULDBLOCK) {
> +                error_report("socket_writev_buffer: Got err=%d for 
> (%zd/%zd)",
> +                             err, size, len);
> +                /*
> +                 * If I've already sent some but only just got the error, I
> +                 * could return the amount validly sent so far and wait for 
> the
> +                 * next call to report the error, but I'd rather flag the 
> error
> +                 * immediately.
> +                 */
> +                return -err;
> +            }
> +
> +            /* Emulate blocking */
> +            GPollFD pfd;
> +
> +            pfd.fd = s->fd;
> +            pfd.events = G_IO_OUT | G_IO_ERR;
> +            pfd.revents = 0;
> +            g_poll(&pfd, 1 /* 1 fd */, -1 /* no timeout */);
> +        }
> +     }
> +
> +    return offset;
>  }
>  
>  static int socket_get_fd(void *opaque)