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>
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@ -1845,7 +1845,7 @@ static int unix_dgram_recvmsg(struct kiocb *iocb, struct socket *sock,
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if (UNIXCB(skb).fp)
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siocb->scm->fp = scm_fp_dup(UNIXCB(skb).fp);
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}
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err = size;
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err = (flags & MSG_TRUNC) ? skb->len - skip : size;
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scm_recv(sock, msg, siocb->scm, flags);
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