Re: [PATCH v2 1/2] QIOChannelSocket: Reduce ifdefs to improve readability

[Daniel P . Berrangé]

On Wed, Jun 08, 2022 at 06:04:02PM -0300, Leonardo Bras wrote:
> During implementation of MSG_ZEROCOPY feature, a lot of #ifdefs were
> introduced, particularly at qio_channel_socket_writev().
> 
> Rewrite some of those changes so it's easier to read.
>                                                                       ...
> Signed-off-by: Leonardo Bras <leobras@redhat.com>
> ---
>  io/channel-socket.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index dc9c165de1..ef7c7cfbac 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -554,6 +554,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
>      size_t fdsize = sizeof(int) * nfds;
>      struct cmsghdr *cmsg;
>      int sflags = 0;
> +    bool zero_copy_enabled = false;
>  
>      memset(control, 0, CMSG_SPACE(sizeof(int) * SOCKET_MAX_FDS));
>  
> @@ -581,6 +582,7 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
>  #ifdef QEMU_MSG_ZEROCOPY
>      if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
>          sflags = MSG_ZEROCOPY;
> +        zero_copy_enabled = true;
>      }

There should be a

 #else
    error_setg(errp, "Zero copy not supported on this platform");
    return -1;
 #endif

>  #endif
>  
> @@ -592,15 +594,13 @@ static ssize_t qio_channel_socket_writev(QIOChannel 
> *ioc,
>              return QIO_CHANNEL_ERR_BLOCK;
>          case EINTR:
>              goto retry;
> -#ifdef QEMU_MSG_ZEROCOPY
>          case ENOBUFS:
> -            if (sflags & MSG_ZEROCOPY) {
> +            if (zero_copy_enabled) {

if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY)

avoids the #ifdef without needing to add yet another
variable expressing what's already expressed in both
'flags' and 'sflags'.

>                  error_setg_errno(errp, errno,
>                                   "Process can't lock enough memory for using 
> MSG_ZEROCOPY");
>                  return -1;
>              }
>              break;
> -#endif
>          }
>  
>          error_setg_errno(errp, errno,
> -- 
> 2.36.1
> 

With regards,
Daniel
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