Re: [PATCH mptcp-next] mptcp: ignore unsupported msg flags

[Florian Westphal <fw@strlen.de>]

Paolo Abeni <pabeni@redhat.com> wrote:
> Currently mptcp_sendmsg()/mptcp_recvmsg() fail with EOPNOTSUPP
> if the user-space provides some unsupported flag. That is
> unexpected and may foul existing applications migrated to MPTCP,
> which expect a different behavior.
> 
> Change the mentioned function to silently ignore the unsupported
> flags.
> 
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/162
> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
>  net/mptcp/protocol.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index 2d895c3c8746..bdec946b9b04 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -1585,8 +1585,8 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
>  	int ret = 0;
>  	long timeo;
>  
> -	if (msg->msg_flags & ~(MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL))
> -		return -EOPNOTSUPP;
> +	/* ignore unsupported flags */
> +	msg->msg_flags &= MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL;

Ignoring MSG_MORE is fine, but DONTWAIT and NOSIGNAL?

I'd prefer hard errors for those until mptcp does the right thing for
them.