From: Daniel Rosenberg <drosen@google.com>
Date: Fri, 12 Feb 2016 00:44:15 +0000 (-0800)
Subject: ANDROID: vfs: add d_canonical_path for stacked filesystem support
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=71b1004af40eef8abcdccf7062689265ceabc1dd;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git

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.

Change-Id: I09563baffad1711a045e45c1bd0bd8713c2cc0b6
Signed-off-by: Daniel Rosenberg <drosen@google.com>
---

diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index 7cc7d3fb1862..5750a477b2a3 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -671,6 +671,8 @@ 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;
@@ -710,13 +712,22 @@ 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, &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;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index f05a659cdf34..d8fcc02e378b 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -149,6 +149,7 @@ struct dentry_operations {
 	int (*d_manage)(const struct path *, bool);
 	struct dentry *(*d_real)(struct dentry *, const struct inode *,
 				 unsigned int, unsigned int);
+	void (*d_canonical_path)(const struct path *, struct path *);
 } ____cacheline_aligned;
 
 /*