linux-kernel - Re: SYSFS: need a noncaching read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 12 Sep 2007 03:01:23 -0700
From:	Greg KH <greg@...ah.com>
To:	Robert Schwebel <r.schwebel@...gutronix.de>
Cc:	Heiko Schocher <hs@...x.de>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, Detlev Zundel <dzu@...x.de>
Subject: Re: SYSFS: need a noncaching read

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.

Not that this is a good thing to do for this kind of thing, as others
have already said.

thanks,

greg k-h
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/