[PATCH 05/19] drm: move dev_mapping to the minor node

[Ilija Hadzic]

On Mon, 30 Apr 2012, Dave Airlie wrote:

> On Mon, Apr 30, 2012 at 6:53 PM, Dave Airlie <airlied at gmail.com> wrote:
>>>
>>> Do you have pointers to that discussion (assuming it was on sime mailing
>>> list)? The least I can do, while I am at it, is try to understand it and
>>> see if I can incorporate some ideas from there in the rework of the patch.
>>
>> Nope it was an offhand discussion on irc while we were talking about
>> some other ugly code.
>
> Okay I think it was the code in coda,
>
>       if (coda_inode->i_mapping == &coda_inode->i_data)
>                coda_inode->i_mapping = host_inode->i_mapping;
>
>        /* only allow additional mmaps as long as userspace isn't changing
>         * the container file on us! */
>        else if (coda_inode->i_mapping != host_inode->i_mapping) {
>                spin_unlock(&cii->c_lock);
>                return -EBUSY;
>        }
>
> We could use code like that to change the i_mapping, instead of failing.
>
> Dave.
>

I have just cut (and sent to the list) a patch that, I believe, implements 
this idea. I did it slightly differently from what coda fs does, but it's 
the same concept. I set i_mapping in the open() instead of moving it 
down to mmap(), because there are so many variants of mmap both in drm and 
GPU-specific drivers, that it would get too messy.

I traced the code quite extensively with printks and it looks like it's 
doing the right thing.

If the new patch seems right, then if and when we add render nodes, the 
original dev_mapping patch that started this thread won't be needed any 
more.

-- Ilija