Hello!
A sample program that demonstrates a situation when rwnd drops to 0 because
of memory pressure and never grows to its original value. At the same time
other association on the same socket has its rwnd affected: it drops to 0,
but restores only to 1.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/socket.h>
#include <unistd.h>
#include <error.h>
#include <fcntl.h>
#include <netinet/in.h>
#include <netinet/sctp.h>
#include <arpa/inet.h>
#include <sys/select.h>
#include <errno.h>
int open_sockets(int *rcsock, int *trsock1, int *trsock2, int *rcbufsize,
struct sockaddr_in *saddr)
{
int optlen, optval;
struct sctp_event_subscribe events;
int ret;
*rcsock = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
if (*rcsock == -1)
return errno;
*trsock1 = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
if (*trsock1 == -1)
return errno;
*trsock2 = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);
if (*trsock1 == -1)
return errno;
optlen = sizeof(optval);
ret = getsockopt(*rcsock, SOL_SOCKET, SO_RCVBUF, &optval, &optlen);
if (ret == -1)
return errno;
printf("Receive socket buffer size: %d\n", optval);
*rcbufsize = optval;
memset(&events, 0, sizeof(events));
events.sctp_data_io_event = 1;
ret = setsockopt(*rcsock, IPPROTO_SCTP, SCTP_EVENTS, &events,
sizeof(events));
if (ret == -1)
return errno;
optval = 1;
ret = setsockopt(*trsock1, IPPROTO_SCTP, SCTP_NODELAY, &optval,
sizeof(optval));
if (ret == -1)
return errno;
ret = setsockopt(*trsock2, IPPROTO_SCTP, SCTP_NODELAY, &optval,
sizeof(optval));
if (ret == -1)
return errno;
saddr->sin_family = AF_INET;
ret = inet_pton(AF_INET, "127.0.0.1", &saddr->sin_addr);
if (ret != 1)
return EFAULT;
saddr->sin_port = htons(54321);
ret = bind(*rcsock, (struct sockaddr *)saddr, sizeof(*saddr));
if (ret == -1)
return errno;
ret = listen(*rcsock, 2);
if (ret == -1)
return errno;
printf("Server is listening on 127.0.0.1:%d...\n",
ntohs(saddr->sin_port));
return 0;
}
/* Fill receive buffer until memory pressure closes rwnd */
int fill_rxbuffer(int rcsock, int trsock1, void *buf, int bufsize,
struct sockaddr_in *saddr, sctp_assoc_t *rcassoc1)
{
int ret;
int optlen;
int rflags;
struct sctp_sndrcvinfo sinfo;
struct sctp_assocparams args;
int total = 0;
int reported = 0;
while (1) {
ret = sctp_sendmsg(trsock1, buf, bufsize,
(struct sockaddr *)saddr,
sizeof(struct sockaddr_in), 0, 0, 0, 0, 0);
if (ret == -1)
return errno;
if (*rcassoc1 == 0) {
rflags = 0;
ret = sctp_recvmsg(rcsock, buf, bufsize, NULL, NULL,
&sinfo, &rflags);
if (ret == -1)
return errno;
if (!(rflags & MSG_NOTIFICATION)) {
*rcassoc1 = sinfo.sinfo_assoc_id;
printf("Receiver association1=%d\n", *rcassoc1);
continue;
}
}
optlen = sizeof(args);
ret = sctp_opt_info(rcsock, *rcassoc1, SCTP_ASSOCINFO, &args,
&optlen);
if (ret == -1)
return errno;
total += bufsize;
if ((total >= reported * 2) || !args.sasoc_local_rwnd) {
reported = total;
printf("Sent %d bytes ... rwnd=%d\n", total,
args.sasoc_local_rwnd);
}
if (!args.sasoc_local_rwnd)
break;
}
return 0;
}
/* Clean the receive buffer */
int free_rxbuffer(int rcsock, void *buf, int bufsize, sctp_assoc_t rcassoc1,
sctp_assoc_t *rcassoc2)
{
int total = 0;
int reported = 0;
int rflags;
struct sctp_sndrcvinfo sinfo;
int ret;
struct sctp_assocparams args;
int optlen;
int err;
while (1) {
rflags = MSG_DONTWAIT;
ret = sctp_recvmsg(rcsock, buf, bufsize, NULL, NULL, &sinfo,
&rflags);
if (ret == -1) {
if ((errno == EWOULDBLOCK) || (errno == EAGAIN))
ret = 0;
else
return errno;
}
if (rflags & MSG_NOTIFICATION)
continue;
if ((*rcassoc2 == 0) && (sinfo.sinfo_assoc_id != rcassoc1)) {
*rcassoc2 = sinfo.sinfo_assoc_id;
printf("Receiver association2=%d\n", *rcassoc2);
}
optlen = sizeof(args);
err = sctp_opt_info(rcsock, rcassoc1, SCTP_ASSOCINFO, &args,
&optlen);
if (err == -1)
return errno;
total += ret;
if ((total >= reported * 2) || !ret) {
reported = total;
printf("Received %d bytes ... rwnd1=%d\n", total,
args.sasoc_local_rwnd);
}
if (!ret)
break;
}
return 0;
}
/* Transmit some packets, give rwnd a chance to restore */
int give_chance(int rcsock, int trsock1, int trsock2, void *buf, int bufsize,
struct sockaddr_in *saddr)
{
/*
* For some reason transmission from here on is really slow.
* Let's send only 2x16 packets, no reason to wait longer,
* there is not improvement any way...
*/
int total = 16;
struct sctp_sndrcvinfo sinfo;
int ret;
int rflags;
printf("Transferring 2x%d packets...\n", total);
while (total--) {
ret = sctp_sendmsg(trsock1, buf, bufsize,
(struct sockaddr *)saddr,
sizeof(struct sockaddr_in), 0, 0, 0, 0, 0);
rflags = 0;
if (ret != -1)
ret = sctp_recvmsg(rcsock, buf, bufsize, NULL, NULL,
&sinfo, &rflags);
if (ret != -1)
ret = sctp_sendmsg(trsock2, buf, bufsize,
(struct sockaddr *)saddr,
sizeof(struct sockaddr_in),
0, 0, 0, 0, 0);
rflags = 0;
if (ret != -1)
ret = sctp_recvmsg(rcsock, buf, bufsize, NULL, NULL,
&sinfo, &rflags);
if (ret == -1) {
if ((errno == EAGAIN) || (errno == EWOULDBLOCK))
printf("We are LOCKED\n");
else
printf("Some unexpected error...\n");
return errno;
}
}
return 0;
}
int main(int argc, char **argv)
{
int rcsock, trsock1, trsock2;
int ret;
int optlen;
struct sockaddr_in saddr;
struct sctp_assocparams args;
sctp_assoc_t rcassoc1 = 0;
sctp_assoc_t rcassoc2 = 0;
char buf[1];
int rcbufsize;
ret = open_sockets(&rcsock, &trsock1, &trsock2, &rcbufsize, &saddr);
if (ret)
exit(ret);
ret = fill_rxbuffer(rcsock, trsock1, &buf, sizeof(buf), &saddr,
&rcassoc1);
if (ret)
exit(ret);
/* Trigger the problem */
ret = sctp_sendmsg(trsock2, &buf, sizeof(buf), (struct sockaddr *)&saddr,
sizeof(struct sockaddr_in), 0, 0, 0, 0, 0);
if (ret == -1)
exit(errno);
ret = free_rxbuffer(rcsock, &buf, sizeof(buf), rcassoc1, &rcassoc2);
if (ret)
exit(ret);
optlen = sizeof(args);
ret = sctp_opt_info(rcsock, rcassoc2, SCTP_ASSOCINFO, &args, &optlen);
if (ret == -1)
exit(errno);
printf("rwnd2=%d\n", args.sasoc_local_rwnd);
ret = give_chance(rcsock, trsock1, trsock2, &buf, sizeof(buf), &saddr);
if (ret)
exit(ret);
optlen = sizeof(args);
ret = sctp_opt_info(rcsock, rcassoc1, SCTP_ASSOCINFO, &args, &optlen);
if (ret == -1)
exit(errno);
printf("rwnd1=%d\n", args.sasoc_local_rwnd);
optlen = sizeof(args);
ret = sctp_opt_info(rcsock, rcassoc2, SCTP_ASSOCINFO, &args, &optlen);
if (ret == -1)
exit(errno);
printf("rwnd2=%d\n", args.sasoc_local_rwnd);
printf("Finished.\n");
close(trsock2);
close(trsock1);
close(rcsock);
}
--
Best regards,
Alexander Sverdlin.
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