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net: Introduce recvmmsg socket syscall

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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>
This commit is contained in:
Arnaldo Carvalho de Melo 2009-10-12 23:40:10 -07:00 • committed by David S. Miller
parent c05e85a06e
commit a2e2725541
25 changed files with 261 additions and 50 deletions
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10
include/linux/socket.h
View file

@ -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 */