diff options
author | David Herrmann <dh.herrmann@gmail.com> | 2014-01-03 14:09:47 +0100 |
---|---|---|
committer | David Herrmann <dh.herrmann@gmail.com> | 2014-03-16 12:17:03 +0100 |
commit | 31bbe16f6d88622d6731fa2cb4ab38d57d844ac1 (patch) | |
tree | 2a123ae13d3e3a9de36f82304b74b8052545cb87 /drivers/gpu/drm/drm_stub.c | |
parent | 786a7828bc74b9b1466e83abb200b75f80f94121 (diff) |
drm: add pseudo filesystem for shared inodes
Our current DRM design uses a single address_space for all users of the
same DRM device. However, there is no way to create an anonymous
address_space without an underlying inode. Therefore, we wait for the
first ->open() callback on a registered char-dev and take-over the inode
of the char-dev. This worked well so far, but has several drawbacks:
- We screw with FS internals and rely on some non-obvious invariants like
inode->i_mapping being the same as inode->i_data for char-devs.
- We don't have any address_space prior to the first ->open() from
user-space. This leads to ugly fallback code and we cannot allocate
global objects early.
As pointed out by Al-Viro, fs/anon_inode.c is *not* supposed to be used by
drivers for anonymous inode-allocation. Therefore, this patch follows the
proposed alternative solution and adds a pseudo filesystem mount-point to
DRM. We can then allocate private inodes including a private address_space
for each DRM device at initialization time.
Note that we could use:
sysfs_get_inode(sysfs_mnt->mnt_sb, drm_device->dev->kobj.sd);
to get access to the underlying sysfs-inode of a "struct device" object.
However, most of this information is currently hidden and it's not clear
whether this address_space is suitable for driver access. Thus, unless
linux allows anonymous address_space objects or driver-core provides a
public inode per device, we're left with our own private internal mount
point.
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Diffstat (limited to 'drivers/gpu/drm/drm_stub.c')
-rw-r--r-- | drivers/gpu/drm/drm_stub.c | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c index 98a33c580ca..f2903d7e3d8 100644 --- a/drivers/gpu/drm/drm_stub.c +++ b/drivers/gpu/drm/drm_stub.c @@ -31,8 +31,10 @@ * DEALINGS IN THE SOFTWARE. */ +#include <linux/fs.h> #include <linux/module.h> #include <linux/moduleparam.h> +#include <linux/mount.h> #include <linux/slab.h> #include <drm/drmP.h> #include <drm/drm_core.h> @@ -416,6 +418,78 @@ void drm_unplug_dev(struct drm_device *dev) } EXPORT_SYMBOL(drm_unplug_dev); +/* + * DRM internal mount + * We want to be able to allocate our own "struct address_space" to control + * memory-mappings in VRAM (or stolen RAM, ...). However, core MM does not allow + * stand-alone address_space objects, so we need an underlying inode. As there + * is no way to allocate an independent inode easily, we need a fake internal + * VFS mount-point. + * + * The drm_fs_inode_new() function allocates a new inode, drm_fs_inode_free() + * frees it again. You are allowed to use iget() and iput() to get references to + * the inode. But each drm_fs_inode_new() call must be paired with exactly one + * drm_fs_inode_free() call (which does not have to be the last iput()). + * We use drm_fs_inode_*() to manage our internal VFS mount-point and share it + * between multiple inode-users. You could, technically, call + * iget() + drm_fs_inode_free() directly after alloc and sometime later do an + * iput(), but this way you'd end up with a new vfsmount for each inode. + */ + +static int drm_fs_cnt; +static struct vfsmount *drm_fs_mnt; + +static const struct dentry_operations drm_fs_dops = { + .d_dname = simple_dname, +}; + +static const struct super_operations drm_fs_sops = { + .statfs = simple_statfs, +}; + +static struct dentry *drm_fs_mount(struct file_system_type *fs_type, int flags, + const char *dev_name, void *data) +{ + return mount_pseudo(fs_type, + "drm:", + &drm_fs_sops, + &drm_fs_dops, + 0x010203ff); +} + +static struct file_system_type drm_fs_type = { + .name = "drm", + .owner = THIS_MODULE, + .mount = drm_fs_mount, + .kill_sb = kill_anon_super, +}; + +static struct inode *drm_fs_inode_new(void) +{ + struct inode *inode; + int r; + + r = simple_pin_fs(&drm_fs_type, &drm_fs_mnt, &drm_fs_cnt); + if (r < 0) { + DRM_ERROR("Cannot mount pseudo fs: %d\n", r); + return ERR_PTR(r); + } + + inode = alloc_anon_inode(drm_fs_mnt->mnt_sb); + if (IS_ERR(inode)) + simple_release_fs(&drm_fs_mnt, &drm_fs_cnt); + + return inode; +} + +static void drm_fs_inode_free(struct inode *inode) +{ + if (inode) { + iput(inode); + simple_release_fs(&drm_fs_mnt, &drm_fs_cnt); + } +} + /** * drm_dev_alloc - Allocate new drm device * @driver: DRM driver to allocate device for |