libnetfilter_conntrack, nfct_catch returns ENOBUFS

[fabien.marotte at mindspeed.com]

Hi,

I develop an application using libnetfilter_conntrack to catch events 
happening in the conntrack system.
I am currently testing the robustness of my application using ab tool 
(connection stress).

libnetfilter_conntrack version is 0.50. I use the new API.
My callback catching the events always returns NFCT_CB_CONTINUE meaning 
that ncft_catch should never returns.

But with 20 (and more) TCP  connections opening simultaneously, nfct_catch 
returns. The error code in errno is 105. Seems to be ENOBUFS.

Looking at the code, I see the comment "ENOBUFS is returned in case that 
nfnetlink is exhausted".

I am very surprised to have memory issues with so few connections.

Could you explain me why this error occurs ? Is this a kernel error 
propagated in user space or is this a user space error ?

Thanks,