405 lines
10 KiB
C
405 lines
10 KiB
C
/*
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* linux/fs/pnode.c
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*
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* (C) Copyright IBM Corporation 2005.
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* Released under GPL v2.
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* Author : Ram Pai (linuxram@us.ibm.com)
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*
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*/
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#include <linux/mnt_namespace.h>
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#include <linux/mount.h>
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#include <linux/fs.h>
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#include <linux/nsproxy.h>
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#include "internal.h"
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#include "pnode.h"
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/* return the next shared peer mount of @p */
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static inline struct mount *next_peer(struct mount *p)
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{
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return list_entry(p->mnt_share.next, struct mount, mnt_share);
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}
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static inline struct mount *first_slave(struct mount *p)
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{
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return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
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}
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static inline struct mount *next_slave(struct mount *p)
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{
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return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
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}
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static struct mount *get_peer_under_root(struct mount *mnt,
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struct mnt_namespace *ns,
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const struct path *root)
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{
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struct mount *m = mnt;
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do {
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/* Check the namespace first for optimization */
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if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
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return m;
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m = next_peer(m);
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} while (m != mnt);
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return NULL;
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}
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/*
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* Get ID of closest dominating peer group having a representative
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* under the given root.
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*
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* Caller must hold namespace_sem
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*/
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int get_dominating_id(struct mount *mnt, const struct path *root)
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{
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struct mount *m;
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for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
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struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
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if (d)
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return d->mnt_group_id;
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}
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return 0;
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}
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static int do_make_slave(struct mount *mnt)
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{
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struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
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struct mount *slave_mnt;
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/*
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* slave 'mnt' to a peer mount that has the
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* same root dentry. If none is available then
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* slave it to anything that is available.
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*/
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while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
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peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;
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if (peer_mnt == mnt) {
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peer_mnt = next_peer(mnt);
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if (peer_mnt == mnt)
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peer_mnt = NULL;
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}
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if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
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list_empty(&mnt->mnt_share))
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mnt_release_group_id(mnt);
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list_del_init(&mnt->mnt_share);
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mnt->mnt_group_id = 0;
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if (peer_mnt)
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master = peer_mnt;
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if (master) {
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list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
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slave_mnt->mnt_master = master;
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list_move(&mnt->mnt_slave, &master->mnt_slave_list);
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list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
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INIT_LIST_HEAD(&mnt->mnt_slave_list);
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} else {
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struct list_head *p = &mnt->mnt_slave_list;
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while (!list_empty(p)) {
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slave_mnt = list_first_entry(p,
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struct mount, mnt_slave);
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list_del_init(&slave_mnt->mnt_slave);
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slave_mnt->mnt_master = NULL;
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}
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}
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mnt->mnt_master = master;
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CLEAR_MNT_SHARED(mnt);
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return 0;
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}
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/*
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* vfsmount lock must be held for write
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*/
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void change_mnt_propagation(struct mount *mnt, int type)
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{
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if (type == MS_SHARED) {
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set_mnt_shared(mnt);
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return;
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}
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do_make_slave(mnt);
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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.mnt_flags |= MNT_UNBINDABLE;
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else
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mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
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}
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}
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/*
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* get the next mount in the propagation tree.
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* @m: the mount seen last
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* @origin: the original mount from where the tree walk initiated
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*
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* Note that peer groups form contiguous segments of slave lists.
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* We rely on that in get_source() to be able to find out if
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* vfsmount found while iterating with propagation_next() is
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* a peer of one we'd found earlier.
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*/
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static struct mount *propagation_next(struct mount *m,
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struct mount *origin)
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{
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/* are there any slaves of this mount? */
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if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
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return first_slave(m);
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while (1) {
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struct mount *master = m->mnt_master;
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if (master == origin->mnt_master) {
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struct mount *next = next_peer(m);
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return (next == origin) ? NULL : next;
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} else if (m->mnt_slave.next != &master->mnt_slave_list)
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return next_slave(m);
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/* back at master */
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m = master;
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}
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}
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static struct mount *next_group(struct mount *m, struct mount *origin)
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{
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while (1) {
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while (1) {
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struct mount *next;
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if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
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return first_slave(m);
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next = next_peer(m);
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if (m->mnt_group_id == origin->mnt_group_id) {
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if (next == origin)
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return NULL;
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} else if (m->mnt_slave.next != &next->mnt_slave)
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break;
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m = next;
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}
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/* m is the last peer */
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while (1) {
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struct mount *master = m->mnt_master;
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if (m->mnt_slave.next != &master->mnt_slave_list)
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return next_slave(m);
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m = next_peer(master);
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if (master->mnt_group_id == origin->mnt_group_id)
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break;
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if (master->mnt_slave.next == &m->mnt_slave)
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break;
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m = master;
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}
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if (m == origin)
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return NULL;
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}
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}
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/* all accesses are serialized by namespace_sem */
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static struct user_namespace *user_ns;
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static struct mount *last_dest, *last_source, *dest_master;
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static struct mountpoint *mp;
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static struct hlist_head *list;
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static int propagate_one(struct mount *m)
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{
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struct mount *child;
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int type;
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/* skip ones added by this propagate_mnt() */
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if (IS_MNT_NEW(m))
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return 0;
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/* skip if mountpoint isn't covered by it */
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if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
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return 0;
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if (m->mnt_group_id == last_dest->mnt_group_id) {
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type = CL_MAKE_SHARED;
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} else {
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struct mount *n, *p;
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for (n = m; ; n = p) {
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p = n->mnt_master;
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if (p == dest_master || IS_MNT_MARKED(p)) {
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while (last_dest->mnt_master != p) {
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last_source = last_source->mnt_master;
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last_dest = last_source->mnt_parent;
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}
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if (n->mnt_group_id != last_dest->mnt_group_id) {
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last_source = last_source->mnt_master;
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last_dest = last_source->mnt_parent;
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}
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break;
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}
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}
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type = CL_SLAVE;
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/* beginning of peer group among the slaves? */
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if (IS_MNT_SHARED(m))
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type |= CL_MAKE_SHARED;
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}
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/* Notice when we are propagating across user namespaces */
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if (m->mnt_ns->user_ns != user_ns)
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type |= CL_UNPRIVILEGED;
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child = copy_tree(last_source, last_source->mnt.mnt_root, type);
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if (IS_ERR(child))
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return PTR_ERR(child);
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mnt_set_mountpoint(m, mp, child);
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last_dest = m;
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last_source = child;
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if (m->mnt_master != dest_master) {
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read_seqlock_excl(&mount_lock);
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SET_MNT_MARK(m->mnt_master);
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read_sequnlock_excl(&mount_lock);
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}
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hlist_add_head(&child->mnt_hash, list);
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return 0;
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}
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/*
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* mount 'source_mnt' under the destination 'dest_mnt' at
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* dentry 'dest_dentry'. And propagate that mount to
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* all the peer and slave mounts of 'dest_mnt'.
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* Link all the new mounts into a propagation tree headed at
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* source_mnt. Also link all the new mounts using ->mnt_list
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* headed at source_mnt's ->mnt_list
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*
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* @dest_mnt: destination mount.
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* @dest_dentry: destination dentry.
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* @source_mnt: source mount.
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* @tree_list : list of heads of trees to be attached.
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*/
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int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
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struct mount *source_mnt, struct hlist_head *tree_list)
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{
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struct mount *m, *n;
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int ret = 0;
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/*
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* we don't want to bother passing tons of arguments to
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* propagate_one(); everything is serialized by namespace_sem,
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* so globals will do just fine.
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*/
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user_ns = current->nsproxy->mnt_ns->user_ns;
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last_dest = dest_mnt;
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last_source = source_mnt;
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mp = dest_mp;
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list = tree_list;
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dest_master = dest_mnt->mnt_master;
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/* all peers of dest_mnt, except dest_mnt itself */
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for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
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ret = propagate_one(n);
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if (ret)
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goto out;
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}
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/* all slave groups */
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for (m = next_group(dest_mnt, dest_mnt); m;
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m = next_group(m, dest_mnt)) {
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/* everything in that slave group */
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n = m;
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do {
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ret = propagate_one(n);
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if (ret)
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goto out;
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n = next_peer(n);
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} while (n != m);
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}
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out:
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read_seqlock_excl(&mount_lock);
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hlist_for_each_entry(n, tree_list, mnt_hash) {
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m = n->mnt_parent;
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if (m->mnt_master != dest_mnt->mnt_master)
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CLEAR_MNT_MARK(m->mnt_master);
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}
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read_sequnlock_excl(&mount_lock);
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return ret;
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}
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/*
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* return true if the refcount is greater than count
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*/
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static inline int do_refcount_check(struct mount *mnt, int count)
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{
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return mnt_get_count(mnt) > count;
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}
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/*
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* check if the mount 'mnt' can be unmounted successfully.
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* @mnt: the mount to be checked for unmount
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* NOTE: unmounting 'mnt' would naturally propagate to all
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* other mounts its parent propagates to.
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* Check if any of these mounts that **do not have submounts**
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* have more references than 'refcnt'. If so return busy.
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*
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* vfsmount lock must be held for write
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*/
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int propagate_mount_busy(struct mount *mnt, int refcnt)
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{
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struct mount *m, *child;
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struct mount *parent = mnt->mnt_parent;
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int ret = 0;
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if (mnt == parent)
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return do_refcount_check(mnt, refcnt);
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/*
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* quickly check if the current mount can be unmounted.
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* If not, we don't have to go checking for all other
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* mounts
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*/
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if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
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return 1;
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for (m = propagation_next(parent, parent); m;
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m = propagation_next(m, parent)) {
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child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
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if (child && list_empty(&child->mnt_mounts) &&
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(ret = do_refcount_check(child, 1)))
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break;
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}
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return ret;
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}
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/*
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* NOTE: unmounting 'mnt' naturally propagates to all other mounts its
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* parent propagates to.
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*/
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static void __propagate_umount(struct mount *mnt)
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{
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struct mount *parent = mnt->mnt_parent;
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struct mount *m;
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BUG_ON(parent == mnt);
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for (m = propagation_next(parent, parent); m;
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m = propagation_next(m, parent)) {
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struct mount *child = __lookup_mnt_last(&m->mnt,
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mnt->mnt_mountpoint);
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/*
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* umount the child only if the child has no
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* other children
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*/
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if (child && list_empty(&child->mnt_mounts)) {
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hlist_del_init_rcu(&child->mnt_hash);
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hlist_add_before_rcu(&child->mnt_hash, &mnt->mnt_hash);
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}
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}
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}
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/*
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* collect all mounts that receive propagation from the mount in @list,
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* and return these additional mounts in the same list.
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* @list: the list of mounts to be unmounted.
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*
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* vfsmount lock must be held for write
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*/
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int propagate_umount(struct hlist_head *list)
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{
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struct mount *mnt;
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hlist_for_each_entry(mnt, list, mnt_hash)
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__propagate_umount(mnt);
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return 0;
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}
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