net: Add MSG_WAITFORONE flag to recvmmsg

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@gmail.com>
Acked-by: Ulrich Drepper <drepper@redhat.com>
Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 7b3aae2052a6..354cc5617f8b 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 769c386bd428..f55ffe9f8c87 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2135,6 +2135,10 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
                         break;
                 ++datagrams;
 
+                /* MSG_WAITFORONE turns on MSG_DONTWAIT after one packet */
+                if (flags & MSG_WAITFORONE)
+                        flags |= MSG_DONTWAIT;
+
                 if (timeout) {
                         ktime_get_ts(timeout);
                         *timeout = timespec_sub(end_time, *timeout);