af_unix: MSG_TRUNC support for dgram sockets
Piergiorgio Beruto expressed the need to fetch size of first datagram in
queue for AF_UNIX sockets and suggested a patch against SIOCINQ ioctl.
I suggested instead to implement MSG_TRUNC support as a recv() input
flag, as already done for RAW, UDP & NETLINK sockets.
len = recv(fd, &byte, 1, MSG_PEEK | MSG_TRUNC);
MSG_TRUNC asks recv() to return the real length of the packet, even when
is was longer than the passed buffer.
There is risk that a userland application used MSG_TRUNC by accident
(since it had no effect on af_unix sockets) and this might break after
this patch.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Tested-by: Piergiorgio Beruto <piergiorgio.beruto@gmail.com>
CC: Michael Kerrisk <mtk.manpages@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 0be4d24..8ee85aa 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1845,7 +1845,7 @@
if (UNIXCB(skb).fp)
siocb->scm->fp = scm_fp_dup(UNIXCB(skb).fp);
}
- err = size;
+ err = (flags & MSG_TRUNC) ? skb->len - skip : size;
scm_recv(sock, msg, siocb->scm, flags);