1 files changed, 84 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
index c23eaf6442ff..dc2c6095d850 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>
@@ -459,6 +461,78 @@ 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
@@ -499,6 +573,13 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
         mutex_init(&dev->struct_mutex);
         mutex_init(&dev->ctxlist_mutex);
 
+        dev->anon_inode = drm_fs_inode_new();
+        if (IS_ERR(dev->anon_inode)) {
+                ret = PTR_ERR(dev->anon_inode);
+                DRM_ERROR("Cannot allocate anonymous inode: %d\n", ret);
+                goto err_free;
+        }
+
         if (drm_core_check_feature(dev, DRIVER_MODESET)) {
                 ret = drm_minor_alloc(dev, DRM_MINOR_CONTROL);
                 if (ret)
@@ -542,6 +623,8 @@ err_minors:
         drm_minor_free(dev, DRM_MINOR_LEGACY);
         drm_minor_free(dev, DRM_MINOR_RENDER);
         drm_minor_free(dev, DRM_MINOR_CONTROL);
+        drm_fs_inode_free(dev->anon_inode);
+err_free:
         kfree(dev);
         return NULL;
 }
@@ -556,6 +639,7 @@ static void drm_dev_release(struct kref *ref)
 
         drm_ctxbitmap_cleanup(dev);
         drm_ht_remove(&dev->map_hash);
+        drm_fs_inode_free(dev->anon_inode);
 
         drm_minor_free(dev, DRM_MINOR_LEGACY);
         drm_minor_free(dev, DRM_MINOR_RENDER);