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vfs: add path_is_mountpoint() helper

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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/[email protected]
Signed-off-by: Ian Kent <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Eric W. Biederman <[email protected]>
Cc: Omar Sandoval <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Al Viro <[email protected]>
This commit is contained in:
Ian Kent 2016-11-24 08:03:41 +11:00 • committed by Al Viro
commit c6609c0a1c
3 changed files with 37 additions and 0 deletions
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29
fs/namespace.c
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@ -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;