Re: [PATCH] Increase the size of the netlink recvmsg buffer

On Sat, 2016-11-12 at 16:23 -0800, dwilder wrote:

> On systems with a large number of network interfaces keepalived may 
> report:
> "Netlink: error: message truncated messages"
> <and>
> "VRRP is trying to assign VIP to unknown qr-dc4f0313-ca interface !!! go 
> out
>   and fix your conf !!!"
> 
> This was reported on a system running OpenStack/Nutron.
> 
> I found that the netlink recvmsg buffer was too small causing messages 
> to be
> truncated. Increasing the buffer from 4K to 8K prevents the problem.
> (linux/netlink.h suggests using an 8K buffer).
> 
> I tested the fix by creating 100 veth interfaces and verifying the 
> errors
> did not return.
> 
> Signed-off-by: David Wilder <[email protected]>
> 
> ---
>   keepalived/vrrp/vrrp_netlink.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/keepalived/vrrp/vrrp_netlink.c 
> b/keepalived/vrrp/vrrp_netlink.c
> index d7adffa..7897b4c 100644
> --- a/keepalived/vrrp/vrrp_netlink.c
> +++ b/keepalived/vrrp/vrrp_netlink.c
> @@ -273,7 +273,7 @@ netlink_parse_info(int (*filter) (struct sockaddr_nl 
> *, struct nlmsghdr *),
>   	int error;
> 
>   	while (1) {
> -		char buf[4096];
> +		char buf[8192];
>   		struct iovec iov = { buf, sizeof buf };
>   		struct sockaddr_nl snl;
>   		struct msghdr msg =

Hi David,

I'm very happy to apply your patch, but since I have been unable to
reproduce the problem, it would be helpful if you could provide some
further information.

1. I haven't been able to see any reference in linux/netlink.h
suggesting an 8k buffer (or any other buffer size). Could you please let
me know where the reference is and/or send a copy of your
linux/netlink.h
2. Could you send a copy of the script you used to create the veth
interfaces, so that I can reproduce it here.
3. What version of Linux are you using?

With many thanks,
Quentin Armitage

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