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Commit 530d9c5f authored by Daniel Rosenberg's avatar Daniel Rosenberg
Browse files

vfs: add d_canonical_path for stacked filesystem support 



Inotify does not currently know when a filesystem
is acting as a wrapper around another fs. This means
that inotify watchers will miss any modifications to
the base file, as well as any made in a separate
stacked fs that points to the same file.
d_canonical_path solves this problem by allowing the fs
to map a dentry to a path in the lower fs. Inotify
can use it to find the appropriate place to watch to
be informed of all changes to a file.

Change-Id: I09563baffad1711a045e45c1bd0bd8713c2cc0b6
Signed-off-by: default avatarDaniel Rosenberg <drosen@google.com>
parent 1e2d3bbc

fs/notify/inotify/inotify_user.c

+14 −3
Original line number Diff line number Diff line
@@ -702,6 +702,8 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname, 
	struct fsnotify_group *group;

	struct inode *inode;

	struct path path;

	struct path alteredpath;

	struct path *canonical_path = &path;

	struct fd f;

	int ret;

	unsigned flags = 0;
@@ -741,13 +743,22 @@ SYSCALL_DEFINE3(inotify_add_watch, int, fd, const char __user *, pathname, 
	if (ret)

		goto fput_and_out;



	/* support stacked filesystems */

	if(path.dentry && path.dentry->d_op) {

		if (path.dentry->d_op->d_canonical_path) {

			path.dentry->d_op->d_canonical_path(path.dentry, &alteredpath);

			canonical_path = &alteredpath;

			path_put(&path);

		}

	}



	/* inode held in place by reference to path; group by fget on fd */

	inode = path.dentry->d_inode;

	inode = canonical_path->dentry->d_inode;

	group = f.file->private_data;



	/* create/update an inode mark */

	ret = inotify_update_watch(group, inode, mask);

	path_put(&path);

	path_put(canonical_path);

fput_and_out:

	fdput(f);

	return ret;
@@ -814,7 +825,7 @@ static int __init inotify_user_setup(void) 
	BUILD_BUG_ON(IN_ISDIR != FS_ISDIR);

	BUILD_BUG_ON(IN_ONESHOT != FS_IN_ONESHOT);



	BUG_ON(hweight32(ALL_INOTIFY_BITS) != 21);

	BUG_ON(hweight32(ALL_INOTIFY_BITS) != 22);



	inotify_inode_mark_cachep = KMEM_CACHE(inotify_inode_mark, SLAB_PANIC);

include/linux/dcache.h

+1 −0
Original line number Diff line number Diff line
@@ -161,6 +161,7 @@ struct dentry_operations { 
	struct vfsmount *(*d_automount)(struct path *);

	int (*d_manage)(struct dentry *, bool);

	struct inode *(*d_select_inode)(struct dentry *, unsigned);

	void (*d_canonical_path)(const struct dentry *, struct path *);

} ____cacheline_aligned;



/*