From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Herrmann Subject: [PATCH v4 1/3] drm: add pseudo filesystem for shared inodes Date: Thu, 23 Jan 2014 13:45:50 +0100 Message-ID: <1390481150-381-1-git-send-email-dh.herrmann@gmail.com> References: <1390480719-434-1-git-send-email-dh.herrmann@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ea0-f171.google.com (mail-ea0-f171.google.com [209.85.215.171]) by gabe.freedesktop.org (Postfix) with ESMTP id 2E471FBF2A for ; Thu, 23 Jan 2014 04:46:08 -0800 (PST) Received: by mail-ea0-f171.google.com with SMTP id h10so402854eak.30 for ; Thu, 23 Jan 2014 04:46:07 -0800 (PST) In-Reply-To: <1390480719-434-1-git-send-email-dh.herrmann@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org Errors-To: dri-devel-bounces+sf-dri-devel=m.gmane.org@lists.freedesktop.org To: dri-devel@lists.freedesktop.org Cc: Al Viro List-Id: dri-devel@lists.freedesktop.org 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 Signed-off-by: David Herrmann --- v4: - export simple_dname drivers/gpu/drm/drm_stub.c | 74 ++++++++++++++++++++++++++++++++++++++++++++++ fs/dcache.c | 1 + 2 files changed, 75 insertions(+) diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c index 98a33c580..f2903d7 100644 --- a/drivers/gpu/drm/drm_stub.c +++ b/drivers/gpu/drm/drm_stub.c @@ -31,8 +31,10 @@ * DEALINGS IN THE SOFTWARE. */ +#include #include #include +#include #include #include #include @@ -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 diff --git a/fs/dcache.c b/fs/dcache.c index 6055d61..27d66b8 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -3107,6 +3107,7 @@ char *simple_dname(struct dentry *dentry, char *buffer, int buflen) end = ERR_PTR(-ENAMETOOLONG); return end; } +EXPORT_SYMBOL(simple_dname); /* * Write full pathname from the root of the filesystem into the buffer. -- 1.8.5.3