Re: [PATCH 02/10] char-socket: rework tcp_chr_recv()

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Sep 03, 2025 at 12:44:02PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> First, qio_channel_readv_full() already guarantees BLOCKING and
> CLOEXEC states for incoming descriptors, no reason call extra
> ioctls.
> 
> Second, current implementation calls _set_block() and _set_cloexec()
> again on old descriptors on failure path - we fix this too.
> 
> Finally, handling errors exactly after qio_channel_readv_full() call
> looks more readable.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  chardev/char-socket.c | 37 +++++++++++++------------------------
>  1 file changed, 13 insertions(+), 24 deletions(-)
> 
> diff --git a/chardev/char-socket.c b/chardev/char-socket.c
> index 1e8313915b..5b9b19ba8b 100644
> --- a/chardev/char-socket.c
> +++ b/chardev/char-socket.c
> @@ -293,6 +293,18 @@ static ssize_t tcp_chr_recv(Chardev *chr, char *buf, size_t len)
>                                       0, &err);
>      }
>  
> +    if (ret == QIO_CHANNEL_ERR_BLOCK) {
> +        errno = EAGAIN;
> +        return -1;
> +    } else if (ret == -1) {
> +        trace_chr_socket_recv_err(chr, chr->label, error_get_pretty(err));
> +        error_free(err);
> +        errno = EIO;
> +        return -1;
> +    }
> +
> +    assert(ret >= 0);

Moving this logic to here means that in the blocking I/O, and/or error
paths, we are not clearing out the previously read s->read_msgfds_num
These should be considered obsolete at the point we start a new read
call, regardless of its success, hence why we had the code ordered in
this way.


> +
>      if (msgfds_num) {
>          /* close and clean read_msgfds */
>          for (i = 0; i < s->read_msgfds_num; i++) {
> @@ -307,30 +319,7 @@ static ssize_t tcp_chr_recv(Chardev *chr, char *buf, size_t len)
>          s->read_msgfds_num = msgfds_num;
>      }
>  
> -    for (i = 0; i < s->read_msgfds_num; i++) {
> -        int fd = s->read_msgfds[i];
> -        if (fd < 0) {
> -            continue;
> -        }
> -
> -        /* O_NONBLOCK is preserved across SCM_RIGHTS so reset it */
> -        qemu_socket_set_block(fd);
> -
> -#ifndef MSG_CMSG_CLOEXEC
> -        qemu_set_cloexec(fd);
> -#endif
> -    }

This for(){} removal is fnie.

> -
> -    if (ret == QIO_CHANNEL_ERR_BLOCK) {
> -        errno = EAGAIN;
> -        ret = -1;
> -    } else if (ret == -1) {
> -        trace_chr_socket_recv_err(chr, chr->label, error_get_pretty(err));
> -        error_free(err);
> -        errno = EIO;
> -    } else if (ret == 0) {
> -        trace_chr_socket_recv_eof(chr, chr->label);
> -    }
> +    trace_chr_socket_recv_eof(chr, chr->label);
>  
>      return ret;
>  }
> -- 
> 2.48.1
> 

With regards,
Daniel
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