drm: track dev_mapping in more robust and flexible way
Setting dev_mapping (pointer to the address_space structure
used for memory mappings) to the address_space of the first
opener's inode and then failing if other openers come in
through a different inode has a few restrictions that are
eliminated by this patch.
If we already have valid dev_mapping and we spot an opener
with different i_node, we force its i_mapping pointer to the
already established address_space structure (first opener's
inode). This will make all mappings from drm device hang off
the same address_space object.
Some benefits (things that now work and didn't work
before) of this patch are:
* user space can mknod and use any number of device
nodes and they will all work fine as long as the major
device number is that of the drm module.
* user space can even remove the first opener's device
nodes and mknod the new one and the applications and
windowing system will still work.
* GPU drivers can safely assume that dev->dev_mapping is
correct address_space and just blindly copy it
into their (private) bdev.dev_mapping
For reference, some discussion that lead to this patch can
be found here:
http://lists.freedesktop.org/archives/dri-devel/2012-April/022283.html
Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index d25a617..5062eec 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -140,12 +140,12 @@
}
if (!retcode) {
mutex_lock(&dev->struct_mutex);
- if (minor->type == DRM_MINOR_LEGACY) {
- if (dev->dev_mapping == NULL)
- dev->dev_mapping = inode->i_mapping;
- else if (dev->dev_mapping != inode->i_mapping)
- retcode = -ENODEV;
- }
+ if (dev->dev_mapping == NULL)
+ dev->dev_mapping = &inode->i_data;
+ /* ihold ensures nobody can remove inode with our i_data */
+ ihold(container_of(dev->dev_mapping, struct inode, i_data));
+ inode->i_mapping = dev->dev_mapping;
+ filp->f_mapping = dev->dev_mapping;
mutex_unlock(&dev->struct_mutex);
}
@@ -509,6 +509,9 @@
}
}
+ BUG_ON(dev->dev_mapping == NULL);
+ iput(container_of(dev->dev_mapping, struct inode, i_data));
+
/* drop the reference held my the file priv */
drm_master_put(&file_priv->master);
file_priv->is_master = 0;