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    SubjectRe: SYSFS: need a noncaching read
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    On Wed, 2007-09-12 at 12:05 +1000, David Gibson wrote:
    > On Tue, Sep 11, 2007 at 11:43:17AM +0200, Heiko Schocher wrote:
    > > Hello,
    > >
    > > I have developed a device driver and use the sysFS to export some
    > > registers to userspace. I opened the sysFS File for one register and did
    > > some reads from this File, but I alwas becoming the same value from the
    > > register, whats not OK, because they are changing. So I found out that
    > > the sysFS caches the reads ... :-(
    > >
    > > Is there a way to retrigger the reads (in that way, that the sysFS
    > > rereads the values from the driver), without closing and opening the
    > > sysFS Files? Or must I better use the ioctl () Driver-interface for
    > > exporting these registers?
    > >
    > > I am asking this, because I must read every 10 ms 2 registers, so
    > > doing a open/read/close for reading one registers is a little bit too
    > > much overhead.
    > >
    > > I made a sysFS seek function, which retriggers the read, and that works
    > > fine, but I have again 2 syscalls, whats also is not optimal.
    > >
    > > Or can we make a open () with a (new?)Flag, that informs the sysFS to
    > > always reread the values from the underlying driver?
    > >
    > > Or a new flag in the "struct attribute_group" in include/linux/sysfs.h,
    > > which let the sysfs rereading the values?
    >
    > This sounds more like sysfs is really not the right interface for
    > polling your registers. You would probably be better off having your
    > driver export a character device from which the register values could
    > be read.

    I thought relay(fs) was the trendy way to do this these days?

    Documentation/filesystems/relay.txt

    cheers

    --
    Michael Ellerman
    OzLabs, IBM Australia Development Lab

    wwweb: http://michael.ellerman.id.au
    phone: +61 2 6212 1183 (tie line 70 21183)

    We do not inherit the earth from our ancestors,
    we borrow it from our children. - S.M.A.R.T Person
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