Re: [PATCH] DAC960 open with O_NONBLOCK

[Christoph Hellwig]

On Mon, Apr 21, 2003 at 10:24:04AM -0700, Dave Olien wrote:
> This "special" file descriptor is created when the driver's open method
> is called with for block special file for controller 0, disk 0,
> with the O_NONBLOCK flag set.  In thsi case, the driver's open method
> bypasses all checks for a disk associated with that file, and doesn't
> increment any reference counts.
> 
> The problem comes at close() time.  This driver code apparently originated
> with linux 2.2, where driver operations were all "file operations".
> In linux 2.2, the driver release method was passed the file descriptor
> that has the O_NONBLOCK flag set.  The release method knows then to not
> decrement reference counts, etc.
>
> In linux 2.4, driver release methods still have a file descriptor argument.
> But, the kernel NEVER passes a non-NULL file argument to the release method.
> So, the DAC960 driver doesn't know that the release method is being called
> for this "special" file descriptor, and improperly decrements reference
> counts.  This makes subsequent opens now work right.

I just went over the same code in 2.5 - the reference counts are
entirely superflous, you can just nuke them.

> I don't like this "special file descriptor" method.  I would have much
> rather created an entry in /proc or something to support these pass through
> commands.  But I imagine there are applications out there that expect
> these special file descriptors.  On the other hand, this HAS been
> broken throught the life on linux 2.4.

What applications?

> I'll be submitting a similar patch to linux 2.5 shortly.

Don't even bother.  Linux 2.5 is the place to fix this issue
correctly.