linux-kernel - Re: error handling in sysfs, fill_read

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Message-ID: <Pine.LNX.4.44L0.0701021045120.4122-100000@iolanthe.rowland.org>
Date:	Tue, 2 Jan 2007 10:47:08 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Oliver Neukum <oliver@...kum.name>, <gregkh@...e.de>,
	<maneesh@...ibm.com>, <linux-kernel@...r.kernel.org>
Subject: Re: error handling in sysfs, fill_read_buffer()

On Tue, 2 Jan 2007, Oliver Neukum wrote:

> Am Dienstag, 2. Januar 2007 16:26 schrieb Alan Stern:
> > On Tue, 2 Jan 2007, Oliver Neukum wrote:
> > 
> > > Hi,
> > > 
> > > if a driver returns an error in fill_read_buffer(), the buffer will be
> > > marked as filled. Subsequent reads will return eof. But there is
> > > no data because of an error, not because it has been read.
> > > Not marking the buffer filled is the obvious fix.
> > > 
> > > 	Regards
> > > 		Oliver
> > > 
> > > Signed-off-by: Oliver Neukum <oliver@...kum.name>
> > > --
> > > 
> > > --- a/fs/sysfs/file.c	2006-12-24 05:00:32.000000000 +0100
> > > +++ b/fs/sysfs/file.c	2007-01-01 15:03:14.000000000 +0100
> > > @@ -70,7 +70,8 @@
> > >   *	Allocate @buffer->page, if it hasn't been already, then call the
> > >   *	kobject's show() method to fill the buffer with this attribute's 
> > >   *	data. 
> > > - *	This is called only once, on the file's first read. 
> > > + *	This is called only once, on the file's first read unless an error
> > > + *	is returned.
> > >   */
> > 
> > I don't think this matches what people expect of sysfs.  If a show method 
> > fails then the assumption is that the file cannot be read at all, so 
> > there's no point in trying to call the method again.
> 
> This would make handling ENOMEM very hard.

No harder than handling any other error: Close the sysfs file, then open 
it and try to read it again.

On the other hand, I agree there's nothing substantively wrong with the 
patch.

Alan Stern

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