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Commit 54b41388 authored by Alessio Balsini's avatar Alessio Balsini
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ANDROID: 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.

Test: Pixel 4.19
Bug: 171780975
Change-Id: I09563baffad1711a045e45c1bd0bd8713c2cc0b6
Signed-off-by: default avatarDaniel Rosenberg <drosen@google.com>
[astrachan: Folded 34df4102216e ("ANDROID: fsnotify: Notify lower fs of
            open") into this patch]
Signed-off-by: default avatarAlistair Strachan <astrachan@google.com>
Signed-off-by: default avatarYongqin Liu <yongqin.liu@linaro.org>
Signed-off-by: default avatarAlessio Balsini <balsini@google.com>
parent c0be21f5

fs/notify/inotify/inotify_user.c

+14 −2
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;
@@ -747,13 +749,23 @@ 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,

							    &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;

include/linux/dcache.h

+2 −1
Original line number Diff line number Diff line
@@ -151,7 +151,8 @@ struct dentry_operations { 
	int (*d_manage)(const struct path *, bool);

	struct dentry *(*d_real)(struct dentry *, const struct inode *);



	ANDROID_KABI_RESERVE(1);

	ANDROID_KABI_USE(1, void (*d_canonical_path)(const struct path *,

						     struct path *));

	ANDROID_KABI_RESERVE(2);

	ANDROID_KABI_RESERVE(3);

	ANDROID_KABI_RESERVE(4);

include/linux/fsnotify.h

+9 −0
Original line number Diff line number Diff line
@@ -211,11 +211,20 @@ static inline void fsnotify_open(struct file *file) 
{

	const struct path *path = &file->f_path;

	struct inode *inode = file_inode(file);

	struct path lower_path;

	__u32 mask = FS_OPEN;



	if (S_ISDIR(inode->i_mode))

		mask |= FS_ISDIR;



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

		path->dentry->d_op->d_canonical_path(path, &lower_path);

		fsnotify_parent(&lower_path, NULL, mask);

		fsnotify(lower_path.dentry->d_inode, mask, &lower_path,

			 FSNOTIFY_EVENT_PATH, NULL, 0);

		path_put(&lower_path);

	}



	fsnotify_parent(path, NULL, mask);

	fsnotify(inode, mask, path, FSNOTIFY_EVENT_PATH, NULL, 0);

}