On Mon, 2012-05-14 at 20:31 +0200, Eric Dumazet wrote:
> On Mon, 2012-05-14 at 20:24 +0200, Juliusz Chroboczek wrote:
> > > There is an API to set ECN on UDP packets.
> > >
> > > setsockopt() IP_TOS, with val = 2
> >
> > Interesting, I didn't realise that. Is it also possible to read the ECN
> > bits?
>
>
> Yep
>
> man 7 ip
>
> IP_RECVTOS (since Linux 2.2)
> If enabled the IP_TOS ancillary message is passed with incoming
> packets.
> It contains a byte which specifies the Type of Service/Precedence field
> of the packet header. Expects a boolean integer flag.
>
>
Here is a quick and dirty UDP echo server (reflecting the TOS and
correct src address on multi homed host )
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <linux/udp.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <arpa/inet.h>
#define PORT 4040
int pktinfo_get(struct msghdr *my_hdr, struct in_pktinfo *pktinfo)
{
int res = -1;
if (my_hdr->msg_controllen > 0) {
struct cmsghdr *get_cmsg;
for (get_cmsg = CMSG_FIRSTHDR(my_hdr); get_cmsg;
get_cmsg = CMSG_NXTHDR(my_hdr, get_cmsg)) {
if (get_cmsg->cmsg_type == IP_PKTINFO) {
struct in_pktinfo *get_pktinfo = (struct
in_pktinfo *)CMSG_DATA(get_cmsg);
memcpy(pktinfo, get_pktinfo, sizeof(*pktinfo));
res = 0;
}
}
}
return res;
}
int tos_get(struct msghdr *my_hdr, unsigned char *tos)
{
int res = -1;
if (my_hdr->msg_controllen > 0) {
struct cmsghdr *get_cmsg;
for (get_cmsg = CMSG_FIRSTHDR(my_hdr); get_cmsg;
get_cmsg = CMSG_NXTHDR(my_hdr, get_cmsg)) {
if (get_cmsg->cmsg_type == IP_TOS) {
unsigned char *pkttos = (unsigned char
*)CMSG_DATA(get_cmsg);
*tos = *pkttos;
res = 0;
}
}
}
return res;
}
int main(int argc, char *argv[])
{
int fd = socket(AF_INET, SOCK_DGRAM, 0);
struct sockaddr_in addr, rem_addr;
int res, on = 1;
struct msghdr msghdr;
struct iovec vec[1];
char cbuf[512];
char frame[4096];
struct in_pktinfo pktinfo;
int c, count = 1000000;
unsigned char last_tos = 0;
while ((c = getopt(argc, argv, "c:")) != -1) {
if (c == 'c') count = atoi(optarg);
}
memset(&addr, 0, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_port = htons(PORT);
if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) == -1) {
perror("bind");
return 1;
}
setsockopt(fd, SOL_IP, IP_PKTINFO, &on, sizeof(on));
setsockopt(fd, SOL_IP, IP_RECVTOS, &on, sizeof(on));
while (1) {
unsigned char tos;
memset(&msghdr, 0, sizeof(msghdr));
msghdr.msg_control = cbuf;
msghdr.msg_controllen = sizeof(cbuf);
msghdr.msg_iov = vec;
msghdr.msg_iovlen = 1;
vec[0].iov_base = frame;
vec[0].iov_len = sizeof(frame);
msghdr.msg_name = &rem_addr;
msghdr.msg_namelen = sizeof(rem_addr);
res = recvmsg(fd, &msghdr, 0);
if (res == -1)
break;
if (pktinfo_get(&msghdr, &pktinfo) == 0) {
// printf("Got IP_PKTINFO dst addr=%s\n",
inet_ntoa(pktinfo.ipi_spec_dst));
}
if (tos_get(&msghdr, &tos) == 0) {
/* IP_TOS option wont be used in sendmsg(), we must use
setsockopt() instead */
if (tos != last_tos) {
if (setsockopt(fd, SOL_IP, IP_TOS, &tos,
sizeof(tos)) == 0)
last_tos = tos;
}
}
/* ok, just echo reply this frame.
* Using sendmsg() will provide IP_PKTINFO back to kernel
* to let it use the 'right' source address
* (destination address of the incoming packet)
*/
vec[0].iov_len = res;
sendmsg(fd, &msghdr, 0);
if (--count == 0)
break;
}
return 0;
}
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