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Commit c6609c0a authored by Ian Kent's avatar Ian Kent Committed by Al Viro
Browse files

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(), that checks if a struct path
is a mountpoint for this case.

Link: http://lkml.kernel.org/r/20161011053358.27645.9729.stgit@pluto.themaw.net


Signed-off-by: default avatarIan Kent <raven@themaw.net>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Omar Sandoval <osandov@osandov.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent fb5f51c7

fs/mount.h

+6 −0
Original line number Diff line number Diff line
@@ -94,6 +94,12 @@ extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *); 
extern int __legitimize_mnt(struct vfsmount *, unsigned);

extern bool legitimize_mnt(struct vfsmount *, unsigned);



static inline bool __path_is_mountpoint(const struct path *path)

{

	struct mount *m = __lookup_mnt(path->mnt, path->dentry);

	return m && likely(!(m->mnt.mnt_flags & MNT_SYNC_UMOUNT));

}



extern void __detach_mounts(struct dentry *dentry);



static inline void detach_mounts(struct dentry *dentry)

fs/namespace.c

+29 −0
Original line number Diff line number Diff line
@@ -1159,6 +1159,35 @@ struct vfsmount *mntget(struct vfsmount *mnt) 
}

EXPORT_SYMBOL(mntget);



/* path_is_mountpoint() - Check if path is a mount in the current

 *                          namespace.

 *

 *  d_mountpoint() can only be used reliably to establish if a dentry is

 *  not mounted in any namespace and that common case is handled inline.

 *  d_mountpoint() isn't aware of the possibility there may be multiple

 *  mounts using a given dentry in a different namespace. This function

 *  checks if the passed in path is a mountpoint rather than the dentry

 *  alone.

 */

bool path_is_mountpoint(const struct path *path)

{

	unsigned seq;

	bool res;



	if (!d_mountpoint(path->dentry))

		return false;



	rcu_read_lock();

	do {

		seq = read_seqbegin(&mount_lock);

		res = __path_is_mountpoint(path);

	} while (read_seqretry(&mount_lock, seq));

	rcu_read_unlock();



	return res;

}

EXPORT_SYMBOL(path_is_mountpoint);



struct vfsmount *mnt_clone_internal(struct path *path)

{

	struct mount *p;

include/linux/mount.h

+2 −0
Original line number Diff line number Diff line
@@ -98,4 +98,6 @@ extern dev_t name_to_dev_t(const char *name); 


extern unsigned int sysctl_mount_max;



extern bool path_is_mountpoint(const struct path *path);



#endif /* _LINUX_MOUNT_H */