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    SubjectRe: [v4l-dvb-maintainer] bttv build error (CONFIG_NET=n)
    On Wed, 31 Oct 2007 04:51:45 -0700 (PDT) Trent Piepho wrote:

    > On Tue, 30 Oct 2007, Randy Dunlap wrote:
    > > drivers/media/video/bt8xx/bttv-cards.c calls ip_compute_csum().
    > > However, when CONFIG_NET=n, that produces:
    > >
    > > ERROR: "ip_compute_csum" [drivers/media/video/bt8xx/bttv.ko] undefined!
    > >
    > > Config symbol VIDEO_BT848 can be made to depend on NET, or the
    > > osprey_eeprom() function can be built depending on some new config
    > > symbol, or bttv could have its own checksum function...
    >
    > The real problem here is that ip_compute_csum is part of lib-y, but is also
    > exported for modules. This problem has come up before, for instance your
    > patch for csum_partial()
    > http://lkml.org/lkml/2007/4/3/209
    >
    > Or the problem with kasprintf and the lg module:
    > http://lkml.org/lkml/2007/9/24/15
    >
    > The general lib-y vs EXPORT_SYMBOL problem:
    > http://lkml.org/lkml/2007/9/25/17
    >
    > The only reason the net stuff works, is because CONFIG_NET includes igmp.c,
    > which can't be compiled as a module. That means ip_compute_csum() will get
    > pulled out of the lib.a file for igmp, and thus be present for the net modules
    > that use it too. If igmp could be turned off, made a module, or stopped using
    > ip_compute_csum(), then the users of ip_compute_csum() that do depend on
    > CONFIG_NET would have the same problem as bttv does.

    Thanks for the analysis and summary.
    (I'm still waiting for those lkml.org links to load... timed out)

    > It seems a shame to create a new ip checksum function in the bttv driver when
    > a perfectly good one already exists and will already be present in just about
    > every kernel out there. Honestly, how common is NET=n and VIDEO_BT848=m
    > outside of randconfig?

    so just adding "depends on NET" should be OK then?

    ---
    ~Randy
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