On Tue, Dec 11, 2012 at 03:18:16PM -0800, Greg KH wrote: > On Wed, Dec 12, 2012 at 12:12:01AM +0100, Benedikt Spranger wrote: > > The documentation has no clear statement to the POSIX 1003.1 mmap() > > feature, wich allows open(), mmap(), close() while the mmaped pointer is > > valid. > > The release() hook inveigled driver programmer to activate owermanagement > > functuonality in the release hook. This may harm. > > > > Signed-off-by: Benedikt Spranger <b.spran...@linutronix.de> > > --- > > Documentation/DocBook/uio-howto.tmpl | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/Documentation/DocBook/uio-howto.tmpl > > b/Documentation/DocBook/uio-howto.tmpl > > index ac3d001..59a886d 100644 > > --- a/Documentation/DocBook/uio-howto.tmpl > > +++ b/Documentation/DocBook/uio-howto.tmpl > > @@ -499,8 +499,13 @@ device is actually used. > > <listitem><para> > > <varname>int (*release)(struct uio_info *info, struct inode *inode) > > </varname>: Optional. If you define your own > > -<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. > > > +</para><para>CAVE: The release hook may be processed, even if a mmap is > > aktive. > > Huh?
I think that's right. You can successfully close() a device while userspace is still using a mapping. If the driver doesn't prevent it, userspace will fail with a SIGBUS when accessing the mapping the next time. > > > +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? In general, I agree. But in this case, I don't think that this is an mmap() feature well known to all programmers (In fact, I wasn't aware of that until Bene told me). Thanks, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
