From: Benedikt Spranger <b.spranger@linutronix.de>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org, hjk@hansjkoch.de,
Alexander.Frank@eberspaecher.com
Subject: Re: [PATCH 1/2] uio: add warning to documentation
Date: Wed, 12 Dec 2012 01:45:34 +0100 [thread overview]
Message-ID: <20121212014534.287c8ba8@linutronix.de> (raw)
In-Reply-To: <20121211231816.GA23621@kroah.com>
On Tue, 11 Dec 2012 15:18:16 -0800
Greg KH <gregkh@linuxfoundation.org> wrote:
> > -<function>open()</function>, you will probably also want a custom
> > +<function>release()</function>, you will probably also want a
> > custom <function>release()</function> function.
> That sentance no longer makes sense.
DUH! will fix...
> > +</para><para>CAVE: The release hook may be processed, even if a
> > mmap is aktive.
> Huh?
OK, think about a user of uio_pdrv_genirq and you did your
powermanagement well. The user open the UIO device, do a mmap() and
close the UIO device. Then he access the given pointer and wonders why
the system is stuck. It is a bad idea to disable clocks on release
while a mmap is active.
> > +Disabling clocks or other powermanagement functionality may cause
> > a system +crash, hangup or other unwanted sideeffects.
> > +</para><para><emphasis>The mmap() function shall add an extra
> > reference to the file associated with the file descriptor fildes
> > which is not removed by a subsequent close() on that file
> > descriptor. This reference shall be removed when there are no more
> > mappings to the file.</emphasis></para><para> +<link
> > xlink:href="http://pubs.opengroup.org/onlinepubs/009695399/functions/mmap.html">IEEE
> > Std 1003.1, 2004 Edition, mmap()</link>
>
> It's not up to us to document the mmap system call here, you should
> know how to use it if you write a program with it, right?
Its not the user of mmap(), it is for the driver programmer. It is a
bad idea to do every kind of powermanagement function in the release
hook.
Regards
Bene
next prev parent reply other threads:[~2012-12-12 0:45 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-11 23:12 [PATCH 0/2] uio: open(), mmap(), close() Benedikt Spranger
2012-12-11 23:12 ` [PATCH 1/2] uio: add warning to documentation Benedikt Spranger
2012-12-11 23:18 ` Greg KH
2012-12-12 0:45 ` Benedikt Spranger [this message]
2012-12-12 4:49 ` Greg KH
2012-12-12 1:56 ` Hans J. Koch
2012-12-12 4:47 ` Greg KH
2012-12-11 23:12 ` [PATCH 2/2] uio: do not expose inode to uio open/release hooks Benedikt Spranger
2012-12-11 23:20 ` Greg KH
2012-12-12 1:42 ` Hans J. Koch
2012-12-12 4:46 ` Greg KH
2012-12-12 8:50 ` Hans J. Koch
2012-12-12 8:56 ` Benedikt Spranger
2012-12-12 15:08 ` Greg KH
2012-12-13 0:08 ` Hans J. Koch
2012-12-13 0:15 ` Greg KH
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