Implement SOCK_CLOEXEC, SOCK_NONBLOCK and MSG_CMSG_CLOEXEC.

This change allows creating file descriptors with close-on-exec set in some
situations. SOCK_CLOEXEC and SOCK_NONBLOCK can be OR'ed in socket() and
socketpair()'s type parameter, and MSG_CMSG_CLOEXEC to recvmsg() makes file
descriptors (SCM_RIGHTS) atomically close-on-exec.

The numerical values for SOCK_CLOEXEC and SOCK_NONBLOCK are as in NetBSD.
MSG_CMSG_CLOEXEC is the first free bit for MSG_*.

The SOCK_* flags are not passed to MAC because this may cause incorrect
failures and can be done later via fcntl() anyway. On the other hand, audit
is expected to cope with the new flags.

For MSG_CMSG_CLOEXEC, unp_externalize() is extended to take a flags
argument.

Reviewed by:	kib

3 files changed, 27 insertions, 4 deletions

diff --git a/lib/libc/sys/recv.2 b/lib/libc/sys/recv.2
index 74f275c..e0a1f04 100644
--- a/lib/libc/sys/recv.2
+++ b/lib/libc/sys/recv.2
@@ -28,7 +28,7 @@
 .\"     @(#)recv.2	8.3 (Berkeley) 2/21/94
 .\" $FreeBSD$
 .\"
-.Dd September 12, 2012
+.Dd March 19, 2013
 .Dt RECV 2
 .Os
 .Sh NAME
@@ -121,11 +121,12 @@ argument to a
 function is formed by
 .Em or Ap ing
 one or more of the values:
-.Bl -column ".Dv MSG_DONTWAIT" -offset indent
+.Bl -column ".Dv MSG_CMSG_CLOEXEC" -offset indent
 .It Dv MSG_OOB Ta process out-of-band data
 .It Dv MSG_PEEK Ta peek at incoming message
 .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
 .El
 .Pp
 The
@@ -227,6 +228,10 @@ and
 .Fa cmsg_type
 set to
 .Dv SCM_RIGHTS .
+The close-on-exec flag on received descriptors is set according to the
+.Dv MSG_CMSG_CLOEXEC
+flag passed to
+.Fn recvmsg .
 .Pp
 Process credentials can also be passed as ancillary data for
 .Dv AF_UNIX
diff --git a/lib/libc/sys/socket.2 b/lib/libc/sys/socket.2
index 24e4293..74730be 100644
--- a/lib/libc/sys/socket.2
+++ b/lib/libc/sys/socket.2
@@ -28,7 +28,7 @@
 .\"     From: @(#)socket.2	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd December 7, 2012
+.Dd March 19, 2013
 .Dt SOCKET 2
 .Os
 .Sh NAME
@@ -115,6 +115,15 @@ which is available only to the super-user, and
 which is planned,
 but not yet implemented, are not described here.
 .Pp
+Additionally, the following flags are allowed in the
+.Fa type
+argument:
+.Pp
+.Bd -literal -offset indent -compact
+SOCK_CLOEXEC	Set close-on-exec on the new descriptor,
+SOCK_NONBLOCK	Set non-blocking mode on the new socket
+.Ed
+.Pp
 The
 .Fa protocol
 argument
diff --git a/lib/libc/sys/socketpair.2 b/lib/libc/sys/socketpair.2
index c86db43..08d00d3 100644
--- a/lib/libc/sys/socketpair.2
+++ b/lib/libc/sys/socketpair.2
@@ -28,7 +28,7 @@
 .\"     @(#)socketpair.2	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
 .\"
-.Dd June 4, 1993
+.Dd March 19, 2013
 .Dt SOCKETPAIR 2
 .Os
 .Sh NAME
@@ -57,6 +57,14 @@ are returned in
 and
 .Fa sv Ns [1] .
 The two sockets are indistinguishable.
+.Pp
+The
+.Dv SOCK_CLOEXEC
+and
+.Dv SOCK_NONBLOCK
+flags in the
+.Fa type
+argument apply to both descriptors.
 .Sh RETURN VALUES
 .Rv -std socketpair
 .Sh ERRORS
@@ -79,6 +87,7 @@ process address space.
 .Sh SEE ALSO
 .Xr pipe 2 ,
 .Xr read 2 ,
+.Xr socket 2 ,
 .Xr write 2
 .Sh HISTORY
 The