lkml.org 
[lkml]   [2012]   [Jul]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: getsockopt/setsockopt with SO_RCVBUF and SO_SNDBUF "non-standard" behaviour
    From
    Date
    On Wed, 2012-07-18 at 17:59 +0200, Eugen Dedu wrote:
    > Any idea?
    >
    > On 17/07/12 11:27, Eugen Dedu wrote:
    > > Hi all,
    > >
    > > I looked on Internet and at the old thread
    > > http://lkml.indiana.edu/hypermail/linux/kernel/0108.0/0275.html, but the
    > > issue is still not settled as far as I see.
    > >
    > > I need to have the highest memory available for snd/rcv buffer and I
    > > need to know/confirm how much it allocated for my process (how much I
    > > can use).
    > >
    > > So with Linux we need to do something like:
    > > setsockopt (..., SO_RCVBUF, 256000, ...)
    > > getsockopt (..., SO_RCVBUF, &i, ...)
    > > i /= 2;
    > >
    > > where i is the size I am looking for.
    > >
    > > Now, to make this code work for other OSes it should be changed to:
    > > setsockopt (..., SO_RCVBUF, 256000, ...)
    > > getsockopt (..., SO_RCVBUF, &i, ...)
    > > #ifdef LINUX
    > > i /= 2;
    > > #endif
    > >
    > > First question, is this code correct? If not, what code gives the amount
    > > of memory useable for my process?
    > >
    > > Second, it seems to me that linux is definitely "non-standard" here.
    > > Saying that linux uses twice as memory has nothing to do with that,
    > > since getsockopt should return what the application can count on, not
    > > what is the internal use. It is like a hypothetical malloc (10) would
    > > return not 10, but 20 (including meta-information). Is that right?
    > >
    > > Cheers,

    That the way it's done on linux since day 0

    You can probably find a lot of pages on the web explaining the
    rationale.

    If your application handles UDP frames, what SO_RCVBUF should count ?

    If its the amount of payload bytes, you could have a pathological
    situation where an attacker sends 1-byte UDP frames fast enough and
    could consume a lot of kernel memory.

    Each frame consumes a fair amount of kernel memory (between 512 bytes
    and 8 Kbytes depending on the driver).

    So linux says : If user expect to receive XXXX bytes, set a limit of
    _kernel_ memory used to store these bytes, and use an estimation of 100%
    of overhead. That is : allow 2*XXXX bytes to be allocated for socket
    receive buffers.





    \
     
     \ /
      Last update: 2012-07-18 19:01    [W:0.027 / U:0.152 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site