Handling -ENOBUFS

[Steve Grubb]

On Wednesday 05 November 2008 15:56:30 Lucas C. Villa Real wrote:
> >> Looking the code at lib/netlink.c, I saw that audit_send() doesn't
> >> handle -ENOBUFS. Would it be possible to replace the condition from
> >> "while (retval < 0 && errno == EINTR)" to "while (retval < 0 && (errno
> >> == EINTR || errno == ENOBUFS))" to fix the problem when sending
> >> packets from userspace to kernel?
> >
> > Have you tried that? Does it fix the problem or just hang the utility?
>
> So far it didn't hang. However, just in case, I added a maximum number
> of retries (currently set to 64). I'm about to launch a new batch to
> stress the system once again, and then I'll be able to see if it works
> as expected.

If it works out, send a patch to the list and I'll pull it into the next 
release.


> >> One interesting thing which I noticed is that 'auditctl -s' doesn't
> >> report that messages were lost,
> >
> > They weren't lost by the audit system so it doesn't know they didn't
> > arrive.
>
> Do you think it would make sense to add an extra member to struct
> sk_buff (a pointer to a callback function) and then have
> skb_queue_tail() signal if it failed to send a message? That would
> allow audit to keep track of such losses, as well as any other
> subsystem using netlink for communicating with userspace.

The network developers generally frown on anything getting added to sk_buff 
since that affects overall system performance. You would probably want to 
take this issue up with them on the net-dev mail list. I would be supportive 
of anything that adds reliability. But they control the code base for that 
part of the kernel.

-Steve