Re: [PATCH v7 1/5] QIOChannel: Add flags on io_writev and introduce io_flush callback

[Peter Xu]

On Thu, Jan 06, 2022 at 07:13:38PM -0300, Leonardo Bras wrote:
> diff --git a/io/channel.c b/io/channel.c
> index e8b019dc36..904855e16e 100644
> --- a/io/channel.c
> +++ b/io/channel.c
> @@ -67,12 +67,13 @@ ssize_t qio_channel_readv_full(QIOChannel *ioc,
>  }
>  
>  
> -ssize_t qio_channel_writev_full(QIOChannel *ioc,
> -                                const struct iovec *iov,
> -                                size_t niov,
> -                                int *fds,
> -                                size_t nfds,
> -                                Error **errp)
> +ssize_t qio_channel_writev_full_flags(QIOChannel *ioc,
> +                                      const struct iovec *iov,
> +                                      size_t niov,
> +                                      int *fds,
> +                                      size_t nfds,
> +                                      int flags,
> +                                      Error **errp)
>  {
>      QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
>  
> @@ -83,7 +84,7 @@ ssize_t qio_channel_writev_full(QIOChannel *ioc,
>          return -1;
>      }

Should we better also check QIO_CHANNEL_FEATURE_WRITE_ZERO_COPY here when
QIO_CHANNEL_WRITE_FLAG_ZERO_COPY is set?  Just like what we do with:

    if ((fds || nfds) &&
        !qio_channel_has_feature(ioc, QIO_CHANNEL_FEATURE_FD_PASS)) {
        error_setg_errno(errp, EINVAL,
                         "Channel does not support file descriptor passing");
        return -1;
    }

I still think it's better to have the caller be crystal clear when to use
zero_copy feature because it has implication on buffer lifetime.

I might have commented similar things before, but I have missed a few versions
so I could also have missed some previous discussions..

>  
> -    return klass->io_writev(ioc, iov, niov, fds, nfds, errp);
> +    return klass->io_writev(ioc, iov, niov, fds, nfds, flags, errp);
>  }

-- 
Peter Xu