Add implementations of sendmmsg(3) and recvmmsg(3) functions which

wraps sendmsg(2) and recvmsg(2) into batch send and receive operation.
The goal of this implementation is only to provide API compatibility
with Linux.

The cancellation behaviour of the functions is not quite right, but
due to relative rare use of cancellation it is considered acceptable
comparing with the complexity of the correct implementation.  If
functions are reimplemented as syscalls, the fix would come almost
trivial.  The direct use of the syscall trampolines instead of libc
wrappers for sendmsg(2) and recvmsg(2) is to avoid data loss on
cancellation.

Submitted by:	Boris Astardzhiev <boris.astardzhiev@gmail.com>
Discussed with:	jilles (cancellation behaviour)
MFC after:	1 month

3 files changed, 135 insertions, 20 deletions

diff --git a/lib/libc/sys/Symbol.map b/lib/libc/sys/Symbol.map
index 7b3257c..dc2ed0e 100644
--- a/lib/libc/sys/Symbol.map
+++ b/lib/libc/sys/Symbol.map
@@ -399,6 +399,8 @@ FBSD_1.4 {
 	utimensat;
 	numa_setaffinity;
 	numa_getaffinity;
+	sendmmsg;
+	recvmmsg;
 };
 
 FBSDprivate_1.0 {
diff --git a/lib/libc/sys/recv.2 b/lib/libc/sys/recv.2
index 326e7ff..4867ea7 100644
--- a/lib/libc/sys/recv.2
+++ b/lib/libc/sys/recv.2
@@ -28,14 +28,15 @@
 .\"     @(#)recv.2	8.3 (Berkeley) 2/21/94
 .\" $FreeBSD$
 .\"
-.Dd October 15, 2014
+.Dd January 29, 2016
 .Dt RECV 2
 .Os
 .Sh NAME
 .Nm recv ,
 .Nm recvfrom ,
-.Nm recvmsg
-.Nd receive a message from a socket
+.Nm recvmsg ,
+.Nm recvmmsg
+.Nd receive message(s) from a socket
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
@@ -47,11 +48,14 @@
 .Fn recvfrom "int s" "void *buf" "size_t len" "int flags" "struct sockaddr * restrict from" "socklen_t * restrict fromlen"
 .Ft ssize_t
 .Fn recvmsg "int s" "struct msghdr *msg" "int flags"
+.Ft ssize_t
+.Fn recvmmsg "int s" "struct mmsghdr * restrict msgvec" "size_t vlen" "int flags" "const struct timespec * restrict timeout"
 .Sh DESCRIPTION
 The
-.Fn recvfrom
+.Fn recvfrom ,
+.Fn recvmsg ,
 and
-.Fn recvmsg
+.Fn recvmmsg
 system calls
 are used to receive messages from a socket,
 and may be used to receive data on a socket whether or not
@@ -84,8 +88,39 @@ null pointer passed as its
 .Fa from
 argument.
 .Pp
-All three routines return the length of the message on successful
-completion.
+The
+.Fn recvmmsg
+function is used to receive multiple
+messages at a call.
+Their number is supplied by
+.Fa vlen .
+The messages are placed in the buffers described by
+.Fa msgvec
+vector, after reception.
+The size of each received message is placed in the
+.Fa msg_len
+field of each element of the vector.
+If
+.Fa timeout
+is NULL the call blocks until the data is available for each
+supplied message buffer.
+Otherwise it waits for data for the specified amount of time.
+If the timeout expired and there is no data received,
+a value 0 is returned.
+The
+.Xr ppoll 2
+system call is used to implement the timeout mechanism,
+before first receive is performed.
+.Pp
+The
+.Fn recv ,
+.Fn recvfrom
+and
+.Fn recvmsg
+return the length of the message on successful
+completion, whereas
+.Fn recvmmsg
+returns the number of received messages.
 If a message is too long to fit in the supplied buffer,
 excess bytes may be discarded depending on the type of socket
 the message is received from (see
@@ -100,7 +135,9 @@ in which case the value
 .Va errno
 is set to
 .Er EAGAIN .
-The receive calls normally return any data available,
+The receive calls except
+.Fn recvmmsg
+normally return any data available,
 up to the requested amount,
 rather than waiting for receipt of the full amount requested;
 this behavior is affected by the socket-level options
@@ -109,6 +146,9 @@ and
 .Dv SO_RCVTIMEO
 described in
 .Xr getsockopt 2 .
+The
+.Fn recvmmsg
+function implements this behaviour for each message in the vector.
 .Pp
 The
 .Xr select 2
@@ -127,6 +167,10 @@ one or more of the values:
 .It Dv MSG_WAITALL Ta wait for full request or error
 .It Dv MSG_DONTWAIT Ta do not block
 .It Dv MSG_CMSG_CLOEXEC Ta set received fds close-on-exec
+.It Dv MSG_WAITFORONE Ta do not block after receiving the first message
+(only for
+.Fn recvmmsg
+)
 .El
 .Pp
 The
@@ -158,6 +202,11 @@ is set to
 This flag is not available in strict
 .Tn ANSI
 or C99 compilation mode.
+The
+.Dv MSG_WAITFORONE
+flag sets MSG_DONTWAIT after the first message has been received.
+This flag is only relevant for
+.Fn recvmmsg .
 .Pp
 The
 .Fn recvmsg
@@ -290,9 +339,31 @@ control data were discarded due to lack of space in the buffer
 for ancillary data.
 .Dv MSG_OOB
 is returned to indicate that expedited or out-of-band data were received.
+.Pp
+The
+.Fn recvmmsg
+system call uses the
+.Fa mmsghdr
+structure, defined as follows in the
+.In sys/socket.h
+header :
+.Bd -literal
+struct mmsghdr {
+	struct msghdr	 msg_hdr;	/* message header */
+	ssize_t		 msg_len;	/* message length */
+};
+.Ed
+.Pp
+On data reception the
+.Fa msg_len
+field is updated to the length of the received message.
 .Sh RETURN VALUES
-These calls return the number of bytes received, or -1
-if an error occurred.
+These calls except
+.Fn recvmmsg
+return the number of bytes received.
+.Fn recvmmsg
+returns the number of messages received.
+A value of -1 is returned if an error occurred.
 .Sh ERRORS
 The calls fail if:
 .Bl -tag -width Er
@@ -347,3 +418,7 @@ The
 .Fn recv
 function appeared in
 .Bx 4.2 .
+The
+.Fn recvmmsg
+function appeared in
+.Fx 11.0 .
diff --git a/lib/libc/sys/send.2 b/lib/libc/sys/send.2
index 8fa2c64..db2f4ee 100644
--- a/lib/libc/sys/send.2
+++ b/lib/libc/sys/send.2
@@ -28,14 +28,15 @@
 .\"     From: @(#)send.2	8.2 (Berkeley) 2/21/94
 .\" $FreeBSD$
 .\"
-.Dd February 5, 2009
+.Dd January 29, 2016
 .Dt SEND 2
 .Os
 .Sh NAME
 .Nm send ,
 .Nm sendto ,
-.Nm sendmsg
-.Nd send a message from a socket
+.Nm sendmsg ,
+.Nm sendmmsg
+.Nd send message(s) from a socket
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
@@ -47,25 +48,33 @@
 .Fn sendto "int s" "const void *msg" "size_t len" "int flags" "const struct sockaddr *to" "socklen_t tolen"
 .Ft ssize_t
 .Fn sendmsg "int s" "const struct msghdr *msg" "int flags"
+.Ft ssize_t
+.Fn sendmmsg "int s" "struct mmsghdr * restrict msgvec" "size_t vlen" "int flags"
 .Sh DESCRIPTION
 The
 .Fn send
-function,
+and
+.Fn sendmmsg
+functions,
 and
 .Fn sendto
 and
 .Fn sendmsg
 system calls
-are used to transmit a message to another socket.
+are used to transmit one or more messages (with the
+.Fn sendmmsg
+call) to
+another socket.
 The
 .Fn send
 function
 may be used only when the socket is in a
 .Em connected
 state, while
-.Fn sendto
-and
+.Fn sendto ,
 .Fn sendmsg
+and
+.Fn sendmmsg
 may be used at any time.
 .Pp
 The address of the target is given by
@@ -81,6 +90,18 @@ underlying protocol, the error
 is returned, and
 the message is not transmitted.
 .Pp
+The
+.Fn sendmmsg
+function sends multiple messages at a call.
+They are given by the
+.Fa msgvec
+vector along with
+.Fa vlen
+specifying the vector size.
+The number of octets sent per each message is placed in the
+.Fa msg_len
+field of each processed element of the vector after transmission.
+.Pp
 No indication of failure to deliver is implicit in a
 .Fn send .
 Locally detected errors are indicated by a return value of -1.
@@ -138,14 +159,27 @@ See
 .Xr recv 2
 for a description of the
 .Fa msghdr
+structure and the
+.Fa mmsghdr
 structure.
 .Sh RETURN VALUES
-The call returns the number of characters sent, or -1
-if an error occurred.
+The
+.Fn send ,
+.Fn sendto
+and
+.Fn sendmsg
+calls
+return the number of octets sent.
+The
+.Fn sendmmsg
+call returns the number of messages sent.
+If an error occurred a value of -1 is returned.
 .Sh ERRORS
 The
 .Fn send
-function and
+and
+.Fn sendmmsg
+functions and
 .Fn sendto
 and
 .Fn sendmsg
@@ -215,6 +249,10 @@ The
 .Fn send
 function appeared in
 .Bx 4.2 .
+The
+.Fn sendmmsg
+function appeared in
+.Fx 11.0 .
 .Sh BUGS
 Because
 .Fn sendmsg