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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 1e2d3bbcf3
commit 530d9c5fc2
2 changed files with 15 additions and 3 deletions
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17
fs/notify/inotify/inotify_user.c
View file

@ -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);

1
include/linux/dcache.h
View file

@ -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;
/*