Subject: Re: iproute uses too small of a receive buffer

From: Eric Dumazet <[email-masked]>
Date: Wed, 28 Oct 2009 08:01:57 +0100

Ben Greear a écrit :
> 
> Probably the right way is to give a cmd-line arg to set the buffer size
> and also continue if the error is ENOBUFs (but print some error out
> so users know they have issues).  I can make the attempt if that
> sounds good to you.

Real fix is to realloc buffer at receive time, no need for user setting.

In my testings I saw it reaching 1 Mbyte
write(2, "REALLOC buflen 8192\n"..., 20) = 20
write(2, "REALLOC buflen 16384\n"..., 21) = 21
write(2, "REALLOC buflen 32768\n"..., 21) = 21
write(2, "REALLOC buflen 65536\n"..., 21) = 21
write(2, "REALLOC buflen 131072\n"..., 22) = 22
write(2, "REALLOC buflen 262144\n"..., 22) = 22
write(2, "REALLOC buflen 524288\n"..., 22) = 22

[iproute2] realloc buffer in rtnl_listen

# ip monitor route
netlink receive error No buffer space available (105)
Dump terminated 

Reported-by: Ben Greear<[email-masked]>
Signed-off-by: Eric Dumazet <[email-masked]>
---
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index b68e2fd..134ce7f 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -392,8 +392,14 @@ int rtnl_listen(struct rtnl_handle *rtnl,
 		.msg_iov = &iov,
 		.msg_iovlen = 1,
 	};
-	char   buf[8192];
+	char   *buf;
+	size_t buflen = 8192;
 
+	buf = malloc(buflen);
+	if (buf == NULL) {
+		fprintf(stderr, "netlink could not alloc %lu bytes\n", buflen);
+		return -1;
+	}
 	memset(&nladdr, 0, sizeof(nladdr));
 	nladdr.nl_family = AF_NETLINK;
 	nladdr.nl_pid = 0;
@@ -401,12 +407,20 @@ int rtnl_listen(struct rtnl_handle *rtnl,
 
 	iov.iov_base = buf;
 	while (1) {
-		iov.iov_len = sizeof(buf);
+		iov.iov_len = buflen;
 		status = recvmsg(rtnl->fd, &msg, 0);
 
 		if (status < 0) {
 			if (errno == EINTR || errno == EAGAIN)
 				continue;
+			if (errno == ENOBUFS) {
+				buf = realloc(buf, buflen * 2);
+				if (buf) {
+					buflen *= 2;
+					iov.iov_base = buf;
+					continue;
+				}
+			}
 			fprintf(stderr, "netlink receive error %s (%d)\n",
 				strerror(errno), errno);
 			return -1;