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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: Ian 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Ian Kent 2016-11-24 08:03:41 +11:00 committed by Al Viro
parent fb5f51c742
commit c6609c0a1c
3 changed files with 37 additions and 0 deletions
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6
fs/mount.h
View File

@ -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)

29
fs/namespace.c
View File

@ -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;

2
include/linux/mount.h
View File

@ -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 */