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    Subject[RFC PATCH 2/8] vfs - add path_is_mountpoint() helper
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    From: Ian Kent <ikent@redhat.com>

    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.

    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>
    ---
    fs/namespace.c | 43 +++++++++++++++++++++++++++++++++++++++++++
    include/linux/fs.h | 2 ++
    2 files changed, 45 insertions(+)

    diff --git a/fs/namespace.c b/fs/namespace.c
    index 7bb2cda..ca1faaa 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -1153,6 +1153,49 @@ struct vfsmount *mntget(struct vfsmount *mnt)
    }
    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 --git a/include/linux/fs.h b/include/linux/fs.h
    index 901e25d..d588b26 100644
    --- a/include/linux/fs.h
    +++ b/include/linux/fs.h
    @@ -2117,6 +2117,8 @@ extern int vfs_ustat(dev_t, struct kstatfs *);
    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);

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      Last update: 2016-10-03 02:51    [W:6.408 / U:0.024 seconds]
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