[PATCH] unbindable mounts
An unbindable mount does not forward or receive propagation. Also unbindable mount disallows bind mounts. The semantics is as follows. Bind semantics: It is invalid to bind mount an unbindable mount. Move semantics: It is invalid to move an unbindable mount under shared mount. Clone-namespace semantics: If a mount is unbindable in the parent namespace, the corresponding cloned mount in the child namespace becomes unbindable too. Note: there is subtle difference, unbindable mounts cannot be bind mounted but can be cloned during clone-namespace. Signed-off-by: Ram Pai <linuxram@us.ibm.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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5afe002213
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9676f0c638
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@ -213,6 +213,16 @@ static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
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return list_entry(next, struct vfsmount, mnt_child);
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}
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static struct vfsmount *skip_mnt_tree(struct vfsmount *p)
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{
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struct list_head *prev = p->mnt_mounts.prev;
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while (prev != &p->mnt_mounts) {
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p = list_entry(prev, struct vfsmount, mnt_child);
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prev = p->mnt_mounts.prev;
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}
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return p;
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}
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static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
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int flag)
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{
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@ -650,6 +660,9 @@ struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
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struct vfsmount *res, *p, *q, *r, *s;
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struct nameidata nd;
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if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(mnt))
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return NULL;
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res = q = clone_mnt(mnt, dentry, flag);
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if (!q)
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goto Enomem;
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@ -661,6 +674,10 @@ struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
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continue;
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for (s = r; s; s = next_mnt(s, r)) {
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if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(s)) {
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s = skip_mnt_tree(s);
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continue;
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}
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while (p != s->mnt_parent) {
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p = p->mnt_parent;
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q = q->mnt_parent;
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@ -698,18 +715,18 @@ Enomem:
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*
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* NOTE: in the table below explains the semantics when a source mount
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* of a given type is attached to a destination mount of a given type.
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* -------------------------------------------------------------
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* | BIND MOUNT OPERATION |
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* |*************************************************************
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* | source-->| shared | private | slave |
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* | dest | | | |
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* | | | | | |
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* | v | | | |
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* |*************************************************************
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* | shared | shared (++) | shared (+) | shared(+++)|
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* | | | | |
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* |non-shared| shared (+) | private | slave (*) |
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* **************************************************************
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* ---------------------------------------------------------------------------
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* | BIND MOUNT OPERATION |
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* |**************************************************************************
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* | source-->| shared | private | slave | unbindable |
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* | dest | | | | |
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* | | | | | | |
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* | v | | | | |
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* |**************************************************************************
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* | shared | shared (++) | shared (+) | shared(+++)| invalid |
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* | | | | | |
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* |non-shared| shared (+) | private | slave (*) | invalid |
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* ***************************************************************************
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* A bind operation clones the source mount and mounts the clone on the
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* destination mount.
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*
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@ -726,18 +743,18 @@ Enomem:
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* (*) the cloned mount is made a slave of the same master as that of the
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* source mount.
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*
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* --------------------------------------------------------------
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* | MOVE MOUNT OPERATION |
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* |*************************************************************
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* | source-->| shared | private | slave |
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* | dest | | | |
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* | | | | | |
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* | v | | | |
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* |*************************************************************
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* | shared | shared (+) | shared (+) | shared(+++) |
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* | | | | |
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* |non-shared| shared (+*) | private | slave (*) |
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* **************************************************************
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* ---------------------------------------------------------------------------
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* | MOVE MOUNT OPERATION |
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* |**************************************************************************
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* | source-->| shared | private | slave | unbindable |
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* | dest | | | | |
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* | | | | | | |
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* | v | | | | |
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* |**************************************************************************
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* | shared | shared (+) | shared (+) | shared(+++) | invalid |
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* | | | | | |
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* |non-shared| shared (+*) | private | slave (*) | unbindable |
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* ***************************************************************************
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*
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* (+) the mount is moved to the destination. And is then propagated to
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* all the mounts in the propagation tree of the destination mount.
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@ -854,6 +871,9 @@ static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
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down_write(&namespace_sem);
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err = -EINVAL;
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if (IS_MNT_UNBINDABLE(old_nd.mnt))
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goto out;
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if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
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goto out;
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@ -911,6 +931,16 @@ static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
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return err;
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}
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static inline int tree_contains_unbindable(struct vfsmount *mnt)
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{
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struct vfsmount *p;
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for (p = mnt; p; p = next_mnt(p, mnt)) {
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if (IS_MNT_UNBINDABLE(p))
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return 1;
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}
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return 0;
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}
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static int do_move_mount(struct nameidata *nd, char *old_name)
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{
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struct nameidata old_nd, parent_nd;
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@ -954,6 +984,12 @@ static int do_move_mount(struct nameidata *nd, char *old_name)
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*/
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if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
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goto out1;
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/*
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* Don't move a mount tree containing unbindable mounts to a destination
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* mount which is shared.
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*/
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if (IS_MNT_SHARED(nd->mnt) && tree_contains_unbindable(old_nd.mnt))
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goto out1;
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err = -ELOOP;
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for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)
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if (p == old_nd.mnt)
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@ -1266,7 +1302,7 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
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data_page);
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else if (flags & MS_BIND)
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retval = do_loopback(&nd, dev_name, flags & MS_REC);
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else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE))
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else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
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retval = do_change_type(&nd, flags);
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else if (flags & MS_MOVE)
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retval = do_move_mount(&nd, dev_name);
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@ -1311,7 +1347,7 @@ int copy_namespace(int flags, struct task_struct *tsk)
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down_write(&namespace_sem);
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/* First pass: copy the tree topology */
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new_ns->root = copy_tree(namespace->root, namespace->root->mnt_root,
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CL_EXPIRE);
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CL_COPY_ALL | CL_EXPIRE);
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if (!new_ns->root) {
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up_write(&namespace_sem);
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kfree(new_ns);
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@ -82,6 +82,8 @@ void change_mnt_propagation(struct vfsmount *mnt, int type)
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if (type != MS_SLAVE) {
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list_del_init(&mnt->mnt_slave);
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mnt->mnt_master = NULL;
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if (type == MS_UNBINDABLE)
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mnt->mnt_flags |= MNT_UNBINDABLE;
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}
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}
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@ -15,6 +15,7 @@
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#define IS_MNT_SLAVE(mnt) (mnt->mnt_master)
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#define IS_MNT_NEW(mnt) (!mnt->mnt_namespace)
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#define CLEAR_MNT_SHARED(mnt) (mnt->mnt_flags &= ~MNT_SHARED)
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#define IS_MNT_UNBINDABLE(mnt) (mnt->mnt_flags & MNT_UNBINDABLE)
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#define CL_EXPIRE 0x01
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#define CL_SLAVE 0x02
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@ -104,6 +104,7 @@ extern int dir_notify_enable;
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#define MS_MOVE 8192
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#define MS_REC 16384
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#define MS_VERBOSE 32768
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#define MS_UNBINDABLE (1<<17) /* change to unbindable */
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#define MS_PRIVATE (1<<18) /* change to private */
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#define MS_SLAVE (1<<19) /* change to slave */
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#define MS_SHARED (1<<20) /* change to shared */
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@ -21,6 +21,7 @@
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#define MNT_NODEV 0x02
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#define MNT_NOEXEC 0x04
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#define MNT_SHARED 0x10 /* if the vfsmount is a shared mount */
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#define MNT_UNBINDABLE 0x20 /* if the vfsmount is a unbindable mount */
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#define MNT_PNODE_MASK 0x30 /* propogation flag mask */
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struct vfsmount {
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