The patch titled
Subject: vfs: add path_is_mountpoint() helper
has been added to the -mm tree. Its filename is
vfs-add-path_is_mountpoint-helper.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/vfs-add-path_is_mountpoint-helper.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/vfs-add-path_is_mountpoint-helper.patch
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------------------------------------------------------
From: Ian Kent <ikent@xxxxxxxxxx>
Subject: vfs: add path_is_mountpoint() helper
d_mountpoint() can only be used reliably to establish if a dentry is
not mounted in any namespace. It isn't aware of the possibility there
may be multiple mounts using a given dentry that may be in a different
namespace.
Add helper functions, path_is_mountpoint() and an rcu version , that
checks if a struct path is a mountpoint for this case.
Link: http://lkml.kernel.org/r/20161011053358.27645.9729.stgit@xxxxxxxxxxxxxxxx
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Omar Sandoval <osandov@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 43 +++++++++++++++++++++++++++++++++++++++++++
include/linux/fs.h | 2 ++
2 files changed, 45 insertions(+)
diff -puN fs/namespace.c~vfs-add-path_is_mountpoint-helper fs/namespace.c
--- a/fs/namespace.c~vfs-add-path_is_mountpoint-helper
+++ a/fs/namespace.c
@@ -1159,6 +1159,49 @@ struct vfsmount *mntget(struct vfsmount
}
EXPORT_SYMBOL(mntget);
+static bool __path_is_mountpoint(struct path *path)
+{
+ struct mount *mount;
+ struct vfsmount *mnt;
+ unsigned seq;
+
+ do {
+ seq = read_seqbegin(&mount_lock);
+ mount = __lookup_mnt(path->mnt, path->dentry);
+ mnt = mount ? &mount->mnt : NULL;
+ } while (mnt &&
+ !(mnt->mnt_flags & MNT_SYNC_UMOUNT) &&
+ read_seqretry(&mount_lock, seq));
+
+ return mnt != NULL;
+}
+
+/* Check if path is a mount in current namespace */
+bool path_is_mountpoint(struct path *path)
+{
+ bool res;
+
+ if (!d_mountpoint(path->dentry))
+ return 0;
+
+ rcu_read_lock();
+ res = __path_is_mountpoint(path);
+ rcu_read_unlock();
+
+ return res;
+}
+EXPORT_SYMBOL(path_is_mountpoint);
+
+/* Check if path is a mount in current namespace */
+bool path_is_mountpoint_rcu(struct path *path)
+{
+ if (!d_mountpoint(path->dentry))
+ return 0;
+
+ return __path_is_mountpoint(path);
+}
+EXPORT_SYMBOL(path_is_mountpoint_rcu);
+
struct vfsmount *mnt_clone_internal(struct path *path)
{
struct mount *p;
diff -puN include/linux/fs.h~vfs-add-path_is_mountpoint-helper include/linux/fs.h
--- a/include/linux/fs.h~vfs-add-path_is_mountpoint-helper
+++ a/include/linux/fs.h
@@ -2134,6 +2134,8 @@ extern int vfs_ustat(dev_t, struct kstat
extern int freeze_super(struct super_block *super);
extern int thaw_super(struct super_block *super);
extern bool our_mnt(struct vfsmount *mnt);
+extern bool path_is_mountpoint(struct path *);
+extern bool path_is_mountpoint_rcu(struct path *);
extern int current_umask(void);
_
Patches currently in -mm which might be from ikent@xxxxxxxxxx are
vfs-change-d_manage-to-take-a-struct-path.patch
vfs-add-path_is_mountpoint-helper.patch
vfs-add-path_has_submounts.patch
autofs-change-autofs4_expire_wait-to-take-struct-path.patch
autofs-change-autofs4_wait-to-take-struct-path.patch
autofs-use-path_is_mountpoint-to-fix-unreliable-d_mountpoint-checks.patch
autofs-use-path_has_submounts-to-fix-unreliable-have_submount-checks.patch
vfs-remove-unused-have_submounts-function.patch
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