[PACKET]: Add optional checksum computation for recvmsg

This patch is needed to make ISC's DHCP server (and probably other
DHCP servers/clients using AF_PACKET) to be able to serve another
client on the same Xen host.

The problem is that packets between different domains on the same
Xen host only have partial checksums.  Unfortunately this piece of
information is not passed along in AF_PACKET unless you're using
the mmap interface.  Since dhcpd doesn't support packet-mmap, UDP
packets from the same host come out with apparently bogus checksums.

This patch adds a mechanism for AF_PACKET recvmsg(2) to return the
status along with the packet.  It does so by adding a new cmsg that
contains this information along with some other relevant data such
as the original packet length.

I didn't include the time stamp information since there is already
a cmsg for that.

This patch also changes the mmap code to set the CSUMNOTREADY flag
on all packets instead of just outoing packets on cooked sockets.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/if_packet.h b/include/linux/if_packet.h
index 99393ef3af39..f3de05c30678 100644
--- a/include/linux/if_packet.h
+++ b/include/linux/if_packet.h
@@ -41,6 +41,7 @@ struct sockaddr_ll
 #define PACKET_RX_RING                  5
 #define PACKET_STATISTICS               6
 #define PACKET_COPY_THRESH              7
+#define PACKET_AUXDATA                  8
 
 struct tpacket_stats
 {
@@ -48,6 +49,15 @@ struct tpacket_stats
         unsigned int    tp_drops;
 };
 
+struct tpacket_auxdata
+{
+        __u32           tp_status;
+        __u32           tp_len;
+        __u32           tp_snaplen;
+        __u16           tp_mac;
+        __u16           tp_net;
+};
+
 struct tpacket_hdr
 {
         unsigned long   tp_status;