net: Introduce recvmmsg socket syscall

Meaning receive multiple messages, reducing the number of syscalls and
net stack entry/exit operations.

Next patches will introduce mechanisms where protocols that want to
optimize this operation will provide an unlocked_recvmsg operation.

This takes into account comments made by:

. Paul Moore: sock_recvmsg is called only for the first datagram,
  sock_recvmsg_nosec is used for the rest.

. Caitlin Bestler: recvmmsg now has a struct timespec timeout, that
  works in the same fashion as the ppoll one.

  If the underlying protocol returns a datagram with MSG_OOB set, this
  will make recvmmsg return right away with as many datagrams (+ the OOB
  one) it has received so far.

. Rémi Denis-Courmont & Steven Whitehouse: If we receive N < vlen
  datagrams and then recvmsg returns an error, recvmmsg will return
  the successfully received datagrams, store the error and return it
  in the next call.

This paves the way for a subsequent optimization, sk_prot->unlocked_recvmsg,
where we will be able to acquire the lock only at batch start and end, not at
every underlying recvmsg call.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 30 insertions, 3 deletions

diff --git a/net/compat.c b/net/compat.c
index a407c3addba..e13f5256fd2 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -727,10 +727,10 @@ EXPORT_SYMBOL(compat_mc_getsockopt);
 
 /* Argument list sizes for compat_sys_socketcall */
 #define AL(x) ((x) * sizeof(u32))
-static unsigned char nas[19]={AL(0),AL(3),AL(3),AL(3),AL(2),AL(3),
+static unsigned char nas[20]={AL(0),AL(3),AL(3),AL(3),AL(2),AL(3),
 				AL(3),AL(3),AL(4),AL(4),AL(4),AL(6),
 				AL(6),AL(2),AL(5),AL(5),AL(3),AL(3),
-				AL(4)};
+				AL(4),AL(5)};
 #undef AL
 
 asmlinkage long compat_sys_sendmsg(int fd, struct compat_msghdr __user *msg, unsigned flags)
@@ -755,13 +755,36 @@ asmlinkage long compat_sys_recvfrom(int fd, void __user *buf, size_t len,
 	return sys_recvfrom(fd, buf, len, flags | MSG_CMSG_COMPAT, addr, addrlen);
 }
 
+asmlinkage long compat_sys_recvmmsg(int fd, struct compat_mmsghdr __user *mmsg,
+				    unsigned vlen, unsigned int flags,
+				    struct timespec __user *timeout)
+{
+	int datagrams;
+	struct timespec ktspec;
+	struct compat_timespec __user *utspec =
+			(struct compat_timespec __user *)timeout;
+
+	if (get_user(ktspec.tv_sec, &utspec->tv_sec) ||
+	    get_user(ktspec.tv_nsec, &utspec->tv_nsec))
+		return -EFAULT;
+
+	datagrams = __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
+				   flags | MSG_CMSG_COMPAT, &ktspec);
+	if (datagrams > 0 &&
+	    (put_user(ktspec.tv_sec, &utspec->tv_sec) ||
+	     put_user(ktspec.tv_nsec, &utspec->tv_nsec)))
+		datagrams = -EFAULT;
+
+	return datagrams;
+}
+
 asmlinkage long compat_sys_socketcall(int call, u32 __user *args)
 {
 	int ret;
 	u32 a[6];
 	u32 a0, a1;
 
-	if (call < SYS_SOCKET || call > SYS_ACCEPT4)
+	if (call < SYS_SOCKET || call > SYS_RECVMMSG)
 		return -EINVAL;
 	if (copy_from_user(a, args, nas[call]))
 		return -EFAULT;
@@ -823,6 +846,10 @@ asmlinkage long compat_sys_socketcall(int call, u32 __user *args)
 	case SYS_RECVMSG:
 		ret = compat_sys_recvmsg(a0, compat_ptr(a1), a[2]);
 		break;
+	case SYS_RECVMMSG:
+		ret = compat_sys_recvmmsg(a0, compat_ptr(a1), a[2], a[3],
+					  compat_ptr(a[4]));
+		break;
 	case SYS_ACCEPT4:
 		ret = sys_accept4(a0, compat_ptr(a1), compat_ptr(a[2]), a[3]);
 		break;