Re: [PATCH 26/33] io/channel-socket: introduce qio_channel_socket_keep_nonblock()

[Peter Xu <peterx@redhat.com>]

On Wed, Aug 13, 2025 at 07:48:47PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Add a possibility to keep socket non-block status when passing
> through qio channel. We need this to support migration of open
> fds through migration channel.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  include/io/channel-socket.h |  3 +++
>  io/channel-socket.c         | 16 ++++++++++++----
>  2 files changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h
> index a88cf8b3a9..0a4327d745 100644
> --- a/include/io/channel-socket.h
> +++ b/include/io/channel-socket.h
> @@ -49,6 +49,7 @@ struct QIOChannelSocket {
>      socklen_t remoteAddrLen;
>      ssize_t zero_copy_queued;
>      ssize_t zero_copy_sent;
> +    bool keep_nonblock;
>  };
>  
>  
> @@ -275,4 +276,6 @@ int qio_channel_socket_set_send_buffer(QIOChannelSocket *ioc,
>                                         size_t size,
>                                         Error **errp);
>  
> +void qio_channel_socket_keep_nonblock(QIOChannel *ioc);
> +
>  #endif /* QIO_CHANNEL_SOCKET_H */
> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index 3b7ca924ff..cd93d7f180 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -462,9 +462,16 @@ static void qio_channel_socket_finalize(Object *obj)
>  }
>  
>  
> +void qio_channel_socket_keep_nonblock(QIOChannel *ioc)
> +{
> +    QIOChannelSocket *sioc = QIO_CHANNEL_SOCKET(ioc);
> +    sioc->keep_nonblock = true;
> +}
> +
> +
>  #ifndef WIN32
>  static void qio_channel_socket_copy_fds(struct msghdr *msg,
> -                                        int **fds, size_t *nfds)
> +                                        int **fds, size_t *nfds, bool set_block)
>  {
>      struct cmsghdr *cmsg;
>  
> @@ -497,8 +504,9 @@ static void qio_channel_socket_copy_fds(struct msghdr *msg,
>                  continue;
>              }
>  
> -            /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
> -            qemu_socket_set_block(fd);
> +            if (set_block) {
> +                qemu_socket_set_block(fd);
> +            }

"keep_nonblock" as a feature in iochannel is slightly hard to digest.  It
can also be read as "keep the fd to be always nonblocking".

Is this feature required, or can this also be done in a get() or
post_load() on the other side to set nonblock to whatever it should be
(that dest QEMU should be aware of)?

>  
>  #ifndef MSG_CMSG_CLOEXEC
>              qemu_set_cloexec(fd);
> @@ -556,7 +564,7 @@ static ssize_t qio_channel_socket_readv(QIOChannel *ioc,
>      }
>  
>      if (fds && nfds) {
> -        qio_channel_socket_copy_fds(&msg, fds, nfds);
> +        qio_channel_socket_copy_fds(&msg, fds, nfds, !sioc->keep_nonblock);
>      }
>  
>      return ret;
> -- 
> 2.48.1
> 
> 

-- 
Peter Xu