Re: /proc/net/tcp not updated fast enough?

[Herbert Xu]

Henrik Christian Grove <grove@xxxxxxxxx> wrote:
 
> I have it running on 11[1] machines and since midnight (it's 11:47 here
> now) I have 2397 succesfull connections, but in 31 cases (that's 1,29%
> of the connections - and thus not totally ignorable) I had to read
> through /proc/net/tcp twice to find the uid. Does that sound plausible,
> or more like I'm doing something wrong?

/proc/net/tcp in 2.4 is inherently unreliable since it doesn't use
the seqfile interface.  Your best bet is to use the tcp_diag interface
instead.  You can either do that by using the ss command from the
iproute2 suite, or you can query tcp_diag directly from C through
netlink.

The latter should be 100% reliable if you do a get instead of a dump.

> If it's plausible, how long can it take for /proc/net/tcp to get the
> info? I'm asking because I see one connection (again since midnight)
> where I don't find any uid in the 5 attempts I do as a max.

It's not that it takes a long time to update /proc/net/tcp, it's
the fact that you have to read /proc/net/tcp in pieces, and when
the underlying data is changing, the 2.4 code is much more prone to
returning things twice or missing entries altogether.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@xxxxxxxxxxxxxxxxxxx>
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