Messages in this thread | | | From | Nick Piggin <> | Subject | Re: SYSFS: need a noncaching read | Date | Wed, 12 Sep 2007 05:19:39 +1000 |
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On Wednesday 12 September 2007 20:01, Greg KH wrote: > On Wed, Sep 12, 2007 at 07:32:07AM +0200, Robert Schwebel wrote: > > On Tue, Sep 11, 2007 at 11:43:17AM +0200, Heiko Schocher wrote: > > > I have developed a device driver and use the sysFS to export some > > > registers to userspace. > > > > Uuuh, uggly. Don't do that. Device drivers are there to abstract things, > > not to play around with registers from 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 ... :-( > > > > Yes, it does. What you can do is close()ing the file handle between > > accesses, which makes it work but is slow. > > Do an lseek back to 0 and then re-read, you will get called in your > driver again.
Can you do a pread with offset 0 to avoid the two syscalls? (which some people seem to be concerned about) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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