Re: New DRM driver model - gets rid of DRM() macros!

[Keith Whitwell <keith@tungstengraphics.com>]

Keith Whitwell wrote:
> Christoph Hellwig wrote:
> 
>> On Wed, Sep 29, 2004 at 02:29:24PM +0100, Keith Whitwell wrote:
>>
>>> Christoph Hellwig wrote:
>>>
>>>
>>>> - drm_flush is a noop.  a NULL ->flush does the same thing, just easier
>>>> - dito or ->poll
>>>> - dito for ->read
>>>
>>>
>>> Pretty sure you couldn't get away with null for these in 2.4, at least.
>>
>>
>>
>> Umm, of course you could.  There's only a hanfull instance defining a
>> ->flush at all.  Similarly all file_ops for regular files and many char
>> devices don't have ->poll.  no ->read is pretty rare but 2.4 chæcks it
>> aswell.
> 
> 
> I tried it, led to crashes (panics, I guess) & the change had to be 
> reverted.  On reverting the crashes stopped.  This was for poll and read:

Thinking about it, it may not have been a problem of crashing, but rather that 
  the behaviour visible from a program attempting to read (or poll) was 
different with noop versions of these functions to NULL versions, and that was 
causing problems.  This is 18 months ago, so yes, I'm being vague.

The X server does look at this file descriptor, which is where the problem 
would have arisen, but only the gamma & maybe ffb drivers do anything with it.

Keith