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

From: Herbert Xu (herbert_at_gondor.apana.org.au)
Date: 10/27/04

  • Next message: Jan Kasprzak: "Re: [PATCH] NFS mount hang fix" 
    To: grove@fsr.ku.dk (Henrik Christian Grove)
Date:	Wed, 27 Oct 2004 22:15:13 +1000

    Henrik Christian Grove <grove@fsr.ku.dk> 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@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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