recv(...,MSG_TRUNC)
Samuel Thibault
Hello,
man recv says, about flags :
MSG_TRUNC
Return the real length of the packet, even when it
was longer than the passed buffer. Only valid for
packet sockets.
But it is neither implemented in ipv4/udp.c, nor in ipv6/udp.c, although
it is in tcp.c, for instance !
By searching with google, I could read old manpages where it didn't exist,
but I find it very useful, especially in conjunction with MSG_PEEK, for
trying to read a packet with a little buffer, and then really get it with
an appropriate buffer.
So here's a patch which cures 2.4.18, and also works on 2.5 kernels.
Best regards,
Samuel Thibault
diff -urN linux-2.4.18/net/ipv4/udp.c linux-2.4.18-cor/net/ipv4/udp.c
--- linux-2.4.18/net/ipv4/udp.c Mon Jun 10 23:34:59 2002
+++ linux-2.4.18-cor/net/ipv4/udp.c Mon Jun 10 23:35:31 2002
@@ -680,7 +680,7 @@
}
if (sk->protinfo.af_inet.cmsg_flags)
ip_cmsg_recv(msg, skb);
- err = copied;
+ err = (flags&MSG_TRUNC) ? skb->len - sizeof(struct udphdr) : copied;
out_free:
skb_free_datagram(sk, skb);
diff -urN linux-2.4.18/net/ipv6/udp.c linux-2.4.18-cor/net/ipv6/udp.c
--- linux-2.4.18/net/ipv6/udp.c Mon Jun 10 23:35:07 2002
+++ linux-2.4.18-cor/net/ipv6/udp.c Mon Jun 10 23:35:36 2002
@@ -432,7 +432,7 @@
}
}
}
- err = copied;
+ err = (flags&MSG_TRUNC) ? skb->len - sizeof(struct udphdr) : copied;
out_free:
skb_free_datagram(sk, skb);
-
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