[RFC v2 0/3] DRM Anonymous Inodes

[David Herrmann]

Hi

On Mon, Jan 20, 2014 at 3:00 AM, Dave Airlie <airlied at gmail.com> wrote:
>>> Hi
>>>
>>> On Fri, Jan 3, 2014 at 3:41 PM, David Herrmann <dh.herrmann at gmail.com> wrote:
>>>> Hi
>>>>
>>>> With 3.13-rc1 the required VFS core changes for anonymous backing inodes in DRM
>>>> got merged. This series reworks the previous patches (I think from early
>>>> August '13) and finally replaces the ugly drm_device->dev_mapping hack.
>>>>
>>>> The patches should be fairly obvious. As I currently only have nouveau here, I'd
>>>> be happy to get some more testers with other drivers.
>>>>
>>>> Patch #1 adds an internal private mount point to DRM core.
>>>> Patch #2 replaces ->dev_mapping with a private anonymous inode for each device.
>>>> Patch #3 removes the delayed dev_mapping initialization in TTM.
>>>>
>>>> The internal mnt-point is based on fs/aio.c and fs/anon_inode.c which do the
>>>> same. It's not clear to me why we cannot share the mnt-point between all these,
>>>> but Al Viro made clear that he will reject any patches on anon_inode.c which do
>>>> that. So lets follow his recommendation and use our own internal mnt-point.
>>> Also tested on i915 ivb now (before: nouveau+TTM). I think this is
>>> ready for 3.14 if nobody finds any issues.
>>
>
> I talked to Al,
>
> 7:13 < viro> umm...
> 17:14 < viro> you do realize that your module will be impossible to unload?
> 17:14 < viro> kern_mount will pin that fs down
> 17:14 < viro> bumping module refcount
> 17:15 < viro> so kern_unmount() in module_exit is not going to be called at all
> 17:15 -!- rafael__ [^rafael at aerd124.neoplus.adsl.tpnet.pl] has quit
> [Ping timeout: 608 seconds]
> 17:16 < viro> what you want is some variation on simple_pin_fs()
> 17:17 < viro> done from drm_dev_alloc()
> 17:18 < viro> with simple_release_fs() from drm_dev_free(), right after iput()
> 17:20 < viro> the export itself is OK (albeit we might be better off
> exporting a variant of mount_pseudo() instead, so that aio and
>               this sucker would both just call mount_dname_pseudo())
> 17:21 < viro> the problem I see there is with kern_mount() use
> 17:47 -!- sameo [~samuel at 192.55.55.41] has quit [Remote host closed
> the connection]
>
> So maybe we should think about it a bit more :-)

So we call simple_pin_fs() in drm_alloc_inode() and add a
drm_free_inode() which calls iput() followed by simple_release_fs()? I
will write up v3 and test with module re-loading this time.

Thanks
David