From 8ec757d0035cdffaca4d6d01093c1f32dc7c9743 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Thu, 3 Aug 2023 17:19:50 +1000 Subject: [PATCH] netlink: Clearer reasoning about the netlink response buffer size Currently we set NLBUFSIZ large enough for 8192 netlink headers (128kiB in total), and reference netlink(7). However netlink(7) says nothing about reponse buffer sizes, and the documents which do reference 8192 *bytes* not 8192 headers. Update NLBUFSIZ to 64kiB with a more detailed rationale. Link: https://bugs.passt.top/show_bug.cgi?id=67 Signed-off-by: David Gibson Signed-off-by: Stefano Brivio --- netlink.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/netlink.c b/netlink.c index 9ff93a4..d5c9439 100644 --- a/netlink.c +++ b/netlink.c @@ -35,7 +35,14 @@ #include "log.h" #include "netlink.h" -#define NLBUFSIZ (8192 * sizeof(struct nlmsghdr)) /* See netlink(7) */ +/* Netlink expects a buffer of at least 8kiB or the system page size, + * whichever is larger. 32kiB is recommended for more efficient. + * Since the largest page size on any remotely common Linux setup is + * 64kiB (ppc64), that should cover it. + * + * https://www.kernel.org/doc/html/next/userspace-api/netlink/intro.html#buffer-sizing + */ +#define NLBUFSIZ 65536 /* Socket in init, in target namespace, sequence (just needs to be monotonic) */ int nl_sock = -1;