From: Heiko Schocher <hs@denx.de>
To: Greg KH <greg@kroah.com>
Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org,
Detlev Zundel <dzu@denx.de>
Subject: Re: SYSFS: need a noncaching read
Date: Wed, 12 Sep 2007 13:59:40 +0200 [thread overview]
Message-ID: <1189598380.6659.28.camel@Zeus.EmbLux> (raw)
In-Reply-To: <20070912113907.GA24087@kroah.com>
Hello Greg,
Am Mittwoch, den 12.09.2007, 04:39 -0700 schrieb Greg KH:
> > > Do an lseek back to 0 and then re-read, you will get called in your
> > > driver again.
> >
> > No thats not true. I thought this too, but if I make a:
> >
> > seek (fd, 0L, SEEK_SET);
> >
> > in Userspace, there is no retrigger in the sysFS, my driver is *not*
> > called again. So I made a own sysfs_seek function, which does retrigger
> > the driver ...
>
> Hm, are you sure? Otherwise the poll() stuff would not work at all.
Yes.
Sysfs uses generic_file_llseek (). And in sysfs_read_file ()
buffer->needs_read_fill must be 1, to reread from the driver.
generic_file_llseek () doesnt change this variable.
Best regards
Heiko
--
DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
WARNING: multiple messages have this Message-ID (diff)
From: Heiko Schocher <hs@denx.de>
To: Greg KH <greg@kroah.com>
Cc: Robert Schwebel <r.schwebel@pengutronix.de>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
Detlev Zundel <dzu@denx.de>
Subject: Re: SYSFS: need a noncaching read
Date: Wed, 12 Sep 2007 13:59:40 +0200 [thread overview]
Message-ID: <1189598380.6659.28.camel@Zeus.EmbLux> (raw)
In-Reply-To: <20070912113907.GA24087@kroah.com>
Hello Greg,
Am Mittwoch, den 12.09.2007, 04:39 -0700 schrieb Greg KH:
> > > Do an lseek back to 0 and then re-read, you will get called in your
> > > driver again.
> >
> > No thats not true. I thought this too, but if I make a:
> >
> > seek (fd, 0L, SEEK_SET);
> >
> > in Userspace, there is no retrigger in the sysFS, my driver is *not*
> > called again. So I made a own sysfs_seek function, which does retrigger
> > the driver ...
>
> Hm, are you sure? Otherwise the poll() stuff would not work at all.
Yes.
Sysfs uses generic_file_llseek (). And in sysfs_read_file ()
buffer->needs_read_fill must be 1, to reread from the driver.
generic_file_llseek () doesnt change this variable.
Best regards
Heiko
--
DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
next prev parent reply other threads:[~2007-09-12 11:57 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-11 9:43 SYSFS: need a noncaching read Heiko Schocher
2007-09-11 9:43 ` Heiko Schocher
2007-09-12 2:05 ` David Gibson
2007-09-12 2:05 ` David Gibson
2007-09-12 3:18 ` Michael Ellerman
2007-09-12 3:18 ` Michael Ellerman
2007-09-12 5:32 ` Robert Schwebel
2007-09-12 5:32 ` Robert Schwebel
2007-09-12 10:01 ` Greg KH
2007-09-12 10:01 ` Greg KH
2007-09-11 19:19 ` Nick Piggin
2007-09-11 19:19 ` Nick Piggin
2007-09-12 17:57 ` Neil Brown
2007-09-12 17:57 ` Neil Brown
2007-09-12 11:13 ` Heiko Schocher
2007-09-12 11:13 ` Heiko Schocher
2007-09-12 11:39 ` Greg KH
2007-09-12 11:39 ` Greg KH
2007-09-12 11:59 ` Heiko Schocher [this message]
2007-09-12 11:59 ` Heiko Schocher
2007-09-17 5:22 ` Tejun Heo
2007-09-17 5:22 ` Tejun Heo
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