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 7cc7d3fb1862fcb557933e63ec66361cf8bcfb7a..5750a477b2a31ea9bfc0419e106964fbafef5ad5 100644 (file)
--- 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 f05a659cdf348a0f2efa2f11b1a932a8f3181482..d8fcc02e378be17e2f83deaa974d7b700cdc6751 100644 (file)
--- 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;
 
 /*