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ANDROID: vfs: add d_canonical_path for stacked filesystem support

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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>
This commit is contained in:
Daniel Rosenberg 2016-02-11 16:44:15 -08:00
parent 819e203358
commit 71b1004af4
2 changed files with 14 additions and 2 deletions
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15
fs/notify/inotify/inotify_user.c
View file

@ -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;

1
include/linux/dcache.h
View file

@ -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;
/*