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>

4 files changed, 23 insertions, 0 deletions

diff --git a/include/linux/net.h b/include/linux/net.h
index 529a0931711d..b42bb60fe92f 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -41,6 +41,7 @@
 #define SYS_SENDMSG     16              /* sys_sendmsg(2)               */
 #define SYS_RECVMSG     17              /* sys_recvmsg(2)               */
 #define SYS_ACCEPT4     18              /* sys_accept4(2)               */
+#define SYS_RECVMMSG    19              /* sys_recvmmsg(2)              */
 
 typedef enum {
         SS_FREE = 0,                    /* not allocated                */
diff --git a/include/linux/socket.h b/include/linux/socket.h
index 3273a0c5043b..59966f12990c 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -65,6 +65,12 @@ struct msghdr {
         unsigned        msg_flags;
 };
 
+/* For recvmmsg/sendmmsg */
+struct mmsghdr {
+        struct msghdr   msg_hdr;
+        unsigned        msg_len;
+};
+
 /*
  *      POSIX 1003.1g - ancillary data object information
  *      Ancillary data consits of a sequence of pairs of
@@ -312,6 +318,10 @@ extern int move_addr_to_user(struct sockaddr *kaddr, int klen, void __user *uadd
 extern int move_addr_to_kernel(void __user *uaddr, int ulen, struct sockaddr *kaddr);
 extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data);
 
+struct timespec;
+
+extern int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
+                          unsigned int flags, struct timespec *timeout);
 #endif
 #endif /* not kernel and not glibc */
 #endif /* _LINUX_SOCKET_H */
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index a990ace1a838..714f063a3e6d 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -25,6 +25,7 @@ struct linux_dirent64;
 struct list_head;
 struct msgbuf;
 struct msghdr;
+struct mmsghdr;
 struct msqid_ds;
 struct new_utsname;
 struct nfsctl_arg;
@@ -677,6 +678,9 @@ asmlinkage long sys_recv(int, void __user *, size_t, unsigned);
 asmlinkage long sys_recvfrom(int, void __user *, size_t, unsigned,
                                 struct sockaddr __user *, int __user *);
 asmlinkage long sys_recvmsg(int fd, struct msghdr __user *msg, unsigned flags);
+asmlinkage long sys_recvmmsg(int fd, struct mmsghdr __user *msg,
+                             unsigned int vlen, unsigned flags,
+                             struct timespec __user *timeout);
 asmlinkage long sys_socket(int, int, int);
 asmlinkage long sys_socketpair(int, int, int, int __user *);
 asmlinkage long sys_socketcall(int call, unsigned long __user *args);
diff --git a/include/net/compat.h b/include/net/compat.h
index 7c3002832d05..9679f05e9896 100644
--- a/include/net/compat.h
+++ b/include/net/compat.h
@@ -18,6 +18,11 @@ struct compat_msghdr {
         compat_uint_t   msg_flags;
 };
 
+struct compat_mmsghdr {
+        struct compat_msghdr msg_hdr;
+        compat_uint_t        msg_len;
+};
+
 struct compat_cmsghdr {
         compat_size_t   cmsg_len;
         compat_int_t    cmsg_level;
@@ -35,6 +40,9 @@ extern int get_compat_msghdr(struct msghdr *, struct compat_msghdr __user *);
 extern int verify_compat_iovec(struct msghdr *, struct iovec *, struct sockaddr *, int);
 extern asmlinkage long compat_sys_sendmsg(int,struct compat_msghdr __user *,unsigned);
 extern asmlinkage long compat_sys_recvmsg(int,struct compat_msghdr __user *,unsigned);
+extern asmlinkage long compat_sys_recvmmsg(int, struct compat_mmsghdr __user *,
+                                           unsigned, unsigned,
+                                           struct timespec __user *);
 extern asmlinkage long compat_sys_getsockopt(int, int, int, char __user *, int __user *);
 extern int put_cmsg_compat(struct msghdr*, int, int, int, void *);