netdev - Re: [PATCH] Add MSG_WAITFORONE flag to recvmmsg

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Date:	Fri, 26 Mar 2010 23:44:30 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Brandon L Black <blblack@...il.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Ulrich Drepper <drepper@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add MSG_WAITFORONE flag to recvmmsg

Le vendredi 26 mars 2010 à 17:35 -0500, Brandon L Black a écrit :
> From: Brandon L Black <blblack@...il.com>
> 
> Add new flag MSG_WAITFORONE for the recvmmsg() syscall.
> When this flag is specified for a blocking socket, recvmmsg()
> will only block until at least 1 packet is available.  The
> default behavior is to block until all vlen packets are
> available.  This flag has no effect on non-blocking sockets
> or when used in combination with MSG_DONTWAIT.
> 
> Signed-off-by: Brandon L Black <blblack@...il.com>


> 
> ---
> diff --git a/include/linux/socket.h b/include/linux/socket.h
> index 7b3aae2..354cc56 100644
> --- a/include/linux/socket.h
> +++ b/include/linux/socket.h
> @@ -255,6 +255,7 @@ struct ucred {
>  #define MSG_ERRQUEUE	0x2000	/* Fetch message from error queue */
>  #define MSG_NOSIGNAL	0x4000	/* Do not generate SIGPIPE */
>  #define MSG_MORE	0x8000	/* Sender will send more */
> +#define MSG_WAITFORONE	0x10000	/* recvmmsg(): block until 1+ packets avail */
>  
>  #define MSG_EOF         MSG_FIN
>  
> diff --git a/net/socket.c b/net/socket.c
> index 769c386..33304d1 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2133,7 +2133,10 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
>  
>  		if (err)
>  			break;
> -		++datagrams;
> +
> +		/* MSG_WAITFORONE turns on MSG_DONTWAIT after one packet */
> +		if (!datagrams++ && (flags & MSG_WAITFORONE))
> +			flags |= MSG_DONTWAIT;


Hmmm, no need to test !datagram, just do :

	++datagrams;

	if (flags & MSG_WAITFORONE)
		flags |= MSG_DONTWAIT;



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