Re: [PATCH v3 1/2] io: Add support for MSG_PEEK for socket channel

[Daniel P . Berrangé]

On Sat, Nov 19, 2022 at 09:36:14AM +0000, manish.mishra wrote:
> MSG_PEEK reads from the peek of channel, The data is treated as
> unread and the next read shall still return this data. This
> support is currently added only for socket class. Extra parameter
> 'flags' is added to io_readv calls to pass extra read flags like
> MSG_PEEK.
> 
> Suggested-by: Daniel P. Berrangé <berrange@redhat.com
> Signed-off-by: manish.mishra <manish.mishra@nutanix.com>
> ---
>  chardev/char-socket.c               |  4 +-
>  include/io/channel.h                | 83 +++++++++++++++++++++++++++++
>  io/channel-buffer.c                 |  1 +
>  io/channel-command.c                |  1 +
>  io/channel-file.c                   |  1 +
>  io/channel-null.c                   |  1 +
>  io/channel-socket.c                 | 16 +++++-
>  io/channel-tls.c                    |  1 +
>  io/channel-websock.c                |  1 +
>  io/channel.c                        | 73 +++++++++++++++++++++++--
>  migration/channel-block.c           |  1 +
>  scsi/qemu-pr-helper.c               |  2 +-
>  tests/qtest/tpm-emu.c               |  2 +-
>  tests/unit/test-io-channel-socket.c |  1 +
>  util/vhost-user-server.c            |  2 +-
>  15 files changed, 179 insertions(+), 11 deletions(-)



> diff --git a/io/channel-socket.c b/io/channel-socket.c
> index b76dca9cc1..a06b24766d 100644
> --- a/io/channel-socket.c
> +++ b/io/channel-socket.c
> @@ -406,6 +406,8 @@ qio_channel_socket_accept(QIOChannelSocket *ioc,
>      }
>  #endif /* WIN32 */
>  
> +    qio_channel_set_feature(QIO_CHANNEL(cioc), 
> QIO_CHANNEL_FEATURE_READ_MSG_PEEK);
> +

This covers the incoming server side socket.

This also needs to be set in outgoing client side socket in
qio_channel_socket_connect_async


> @@ -705,7 +718,6 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
>  }
>  #endif /* WIN32 */
>  
> -
>  #ifdef QEMU_MSG_ZEROCOPY
>  static int qio_channel_socket_flush(QIOChannel *ioc,
>                                      Error **errp)

Please remove this unrelated whitespace change.


> @@ -109,6 +117,37 @@ int qio_channel_readv_all_eof(QIOChannel *ioc,
>      return qio_channel_readv_full_all_eof(ioc, iov, niov, NULL, NULL, errp);
>  }
>  
> +int qio_channel_readv_peek_all_eof(QIOChannel *ioc,
> +                                   const struct iovec *iov,
> +                                   size_t niov,
> +                                   Error **errp)
> +{
> +   ssize_t len = 0;
> +   ssize_t total = iov_size(iov, niov);
> +
> +   while (len < total) {
> +       len = qio_channel_readv_full(ioc, iov, niov, NULL,
> +                                    NULL, QIO_CHANNEL_READ_FLAG_MSG_PEEK, 
> errp);
> +
> +       if (len == QIO_CHANNEL_ERR_BLOCK) {
> +            if (qemu_in_coroutine()) {
> +                qio_channel_yield(ioc, G_IO_IN);
> +            } else {
> +                qio_channel_wait(ioc, G_IO_IN);
> +            }
> +            continue;
> +       }
> +       if (len == 0) {
> +           return 0;
> +       }
> +       if (len < 0) {
> +           return -1;
> +       }
> +   }

This will busy wait burning CPU where there is a read > 0 and < total.


With regards,
Daniel
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