| 1 | |
| 2 | * linux/fs/pnode.c
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| 3 | *
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| 4 | * (C) Copyright IBM Corporation 2005.
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| 5 | * Released under GPL v2.
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| 6 | * Author : Ram Pai ([email protected])
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| 7 | *
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| 8 |
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| 9 | #include <linux/mnt_namespace.h>
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| 10 | #include <linux/mount.h>
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| 11 | #include <linux/fs.h>
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| 12 | #include "internal.h"
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| 13 | #include "pnode.h"
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| 14 |
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| 15 |
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| 16 | static inline struct mount *next_peer(struct mount *p)
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| 17 | {
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| 18 | return list_entry(p->mnt_share.next, struct mount, mnt_share);
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| 19 | }
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| 20 |
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| 21 | static inline struct mount *first_slave(struct mount *p)
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| 22 | {
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| 23 | return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
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| 24 | }
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| 25 |
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| 26 | static inline struct mount *next_slave(struct mount *p)
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| 27 | {
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| 28 | return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
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| 29 | }
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| 30 |
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| 31 | static struct mount *get_peer_under_root(struct mount *mnt,
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| 32 | struct mnt_namespace *ns,
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| 33 | const struct path *root)
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| 34 | {
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| 35 | struct mount *m = mnt;
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| 36 |
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| 37 | do {
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| 38 |
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| 39 | if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
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| 40 | return m;
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| 41 |
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| 42 | m = next_peer(m);
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| 43 | } while (m != mnt);
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| 44 |
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| 45 | return NULL;
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| 46 | }
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| 47 |
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| 48 | |
| 49 | * Get ID of closest dominating peer group having a representative
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| 50 | * under the given root.
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| 51 | *
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| 52 | * Caller must hold namespace_sem
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| 53 |
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| 54 | int get_dominating_id(struct mount *mnt, const struct path *root)
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| 55 | {
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| 56 | struct mount *m;
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| 57 |
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| 58 | for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
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| 59 | struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
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| 60 | if (d)
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| 61 | return d->mnt_group_id;
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| 62 | }
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| 63 |
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| 64 | return 0;
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| 65 | }
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| 66 |
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| 67 | static int do_make_slave(struct mount *mnt)
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| 68 | {
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| 69 | struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
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| 70 | struct mount *slave_mnt;
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| 71 |
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| 72 | |
| 73 | * slave 'mnt' to a peer mount that has the
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| 74 | * same root dentry. If none is available then
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| 75 | * slave it to anything that is available.
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| 76 |
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| 77 | while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
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| 78 | peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;
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| 79 |
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| 80 | if (peer_mnt == mnt) {
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| 81 | peer_mnt = next_peer(mnt);
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| 82 | if (peer_mnt == mnt)
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| 83 | peer_mnt = NULL;
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| 84 | }
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| 85 | if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
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| 86 | mnt_release_group_id(mnt);
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| 87 |
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| 88 | list_del_init(&mnt->mnt_share);
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| 89 | mnt->mnt_group_id = 0;
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| 90 |
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| 91 | if (peer_mnt)
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| 92 | master = peer_mnt;
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| 93 |
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| 94 | if (master) {
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| 95 | list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
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| 96 | slave_mnt->mnt_master = master;
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| 97 | list_move(&mnt->mnt_slave, &master->mnt_slave_list);
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| 98 | list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
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| 99 | INIT_LIST_HEAD(&mnt->mnt_slave_list);
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| 100 | } else {
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| 101 | struct list_head *p = &mnt->mnt_slave_list;
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| 102 | while (!list_empty(p)) {
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| 103 | slave_mnt = list_first_entry(p,
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| 104 | struct mount, mnt_slave);
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| 105 | list_del_init(&slave_mnt->mnt_slave);
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| 106 | slave_mnt->mnt_master = NULL;
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| 107 | }
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| 108 | }
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| 109 | mnt->mnt_master = master;
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| 110 | CLEAR_MNT_SHARED(mnt);
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| 111 | return 0;
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| 112 | }
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| 113 |
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| 114 | |
| 115 | * vfsmount lock must be held for write
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| 116 |
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| 117 | void change_mnt_propagation(struct mount *mnt, int type)
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| 118 | {
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| 119 | if (type == MS_SHARED) {
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| 120 | set_mnt_shared(mnt);
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| 121 | return;
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| 122 | }
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| 123 | do_make_slave(mnt);
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| 124 | if (type != MS_SLAVE) {
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| 125 | list_del_init(&mnt->mnt_slave);
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| 126 | mnt->mnt_master = NULL;
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| 127 | if (type == MS_UNBINDABLE)
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| 128 | mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
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| 129 | else
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| 130 | mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
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| 131 | }
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| 132 | }
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| 133 |
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| 134 | |
| 135 | * get the next mount in the propagation tree.
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| 136 | * @m: the mount seen last
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| 137 | * @origin: the original mount from where the tree walk initiated
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| 138 | *
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| 139 | * Note that peer groups form contiguous segments of slave lists.
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| 140 | * We rely on that in get_source() to be able to find out if
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| 141 | * vfsmount found while iterating with propagation_next() is
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| 142 | * a peer of one we'd found earlier.
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| 143 |
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| 144 | static struct mount *propagation_next(struct mount *m,
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| 145 | struct mount *origin)
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| 146 | {
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| 147 |
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| 148 | if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
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| 149 | return first_slave(m);
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| 150 |
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| 151 | while (1) {
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| 152 | struct mount *master = m->mnt_master;
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| 153 |
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| 154 | if (master == origin->mnt_master) {
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| 155 | struct mount *next = next_peer(m);
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| 156 | return (next == origin) ? NULL : next;
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| 157 | } else if (m->mnt_slave.next != &master->mnt_slave_list)
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| 158 | return next_slave(m);
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| 159 |
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| 160 |
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| 161 | m = master;
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| 162 | }
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| 163 | }
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| 164 |
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| 165 | |
| 166 | * return the source mount to be used for cloning
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| 167 | *
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| 168 | * @dest the current destination mount
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| 169 | * @last_dest the last seen destination mount
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| 170 | * @last_src the last seen source mount
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| 171 | * @type return CL_SLAVE if the new mount has to be
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| 172 | * cloned as a slave.
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| 173 |
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| 174 | static struct mount *get_source(struct mount *dest,
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| 175 | struct mount *last_dest,
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| 176 | struct mount *last_src,
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| 177 | int *type)
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| 178 | {
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| 179 | struct mount *p_last_src = NULL;
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| 180 | struct mount *p_last_dest = NULL;
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| 181 |
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| 182 | while (last_dest != dest->mnt_master) {
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| 183 | p_last_dest = last_dest;
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| 184 | p_last_src = last_src;
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| 185 | last_dest = last_dest->mnt_master;
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| 186 | last_src = last_src->mnt_master;
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| 187 | }
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| 188 |
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| 189 | if (p_last_dest) {
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| 190 | do {
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| 191 | p_last_dest = next_peer(p_last_dest);
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| 192 | } while (IS_MNT_NEW(p_last_dest));
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| 193 |
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| 194 | if (dest == p_last_dest) {
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| 195 | *type = CL_MAKE_SHARED;
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| 196 | return p_last_src;
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| 197 | }
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| 198 | }
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| 199 |
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| 200 | *type = CL_SLAVE;
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| 201 |
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| 202 | if (IS_MNT_SHARED(dest))
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| 203 | *type |= CL_MAKE_SHARED;
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| 204 | return last_src;
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| 205 | }
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| 206 |
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| 207 | |
| 208 | * mount 'source_mnt' under the destination 'dest_mnt' at
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| 209 | * dentry 'dest_dentry'. And propagate that mount to
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| 210 | * all the peer and slave mounts of 'dest_mnt'.
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| 211 | * Link all the new mounts into a propagation tree headed at
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| 212 | * source_mnt. Also link all the new mounts using ->mnt_list
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| 213 | * headed at source_mnt's ->mnt_list
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| 214 | *
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| 215 | * @dest_mnt: destination mount.
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| 216 | * @dest_dentry: destination dentry.
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| 217 | * @source_mnt: source mount.
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| 218 | * @tree_list : list of heads of trees to be attached.
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| 219 |
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| 220 | int propagate_mnt(struct mount *dest_mnt, struct dentry *dest_dentry,
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| 221 | struct mount *source_mnt, struct list_head *tree_list)
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| 222 | {
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| 223 | struct mount *m, *child;
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| 224 | int ret = 0;
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| 225 | struct mount *prev_dest_mnt = dest_mnt;
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| 226 | struct mount *prev_src_mnt = source_mnt;
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| 227 | LIST_HEAD(tmp_list);
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| 228 | LIST_HEAD(umount_list);
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| 229 |
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| 230 | for (m = propagation_next(dest_mnt, dest_mnt); m;
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| 231 | m = propagation_next(m, dest_mnt)) {
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| 232 | int type;
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| 233 | struct mount *source;
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| 234 |
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| 235 | if (IS_MNT_NEW(m))
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| 236 | continue;
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| 237 |
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| 238 | source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
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| 239 |
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| 240 | if (!(child = copy_tree(source, source->mnt.mnt_root, type))) {
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| 241 | ret = -ENOMEM;
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| 242 | list_splice(tree_list, tmp_list.prev);
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| 243 | goto out;
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| 244 | }
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| 245 |
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| 246 | if (is_subdir(dest_dentry, m->mnt.mnt_root)) {
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| 247 | mnt_set_mountpoint(m, dest_dentry, child);
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| 248 | list_add_tail(&child->mnt_hash, tree_list);
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| 249 | } else {
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| 250 | |
| 251 | * This can happen if the parent mount was bind mounted
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| 252 | * on some subdirectory of a shared/slave mount.
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| 253 |
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| 254 | list_add_tail(&child->mnt_hash, &tmp_list);
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| 255 | }
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| 256 | prev_dest_mnt = m;
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| 257 | prev_src_mnt = child;
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| 258 | }
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| 259 | out:
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| 260 | br_write_lock(&vfsmount_lock);
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| 261 | while (!list_empty(&tmp_list)) {
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| 262 | child = list_first_entry(&tmp_list, struct mount, mnt_hash);
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| 263 | umount_tree(child, 0, &umount_list);
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| 264 | }
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| 265 | br_write_unlock(&vfsmount_lock);
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| 266 | release_mounts(&umount_list);
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| 267 | return ret;
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| 268 | }
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| 269 |
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| 270 | |
| 271 | * return true if the refcount is greater than count
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| 272 |
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| 273 | static inline int do_refcount_check(struct mount *mnt, int count)
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| 274 | {
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| 275 | int mycount = mnt_get_count(mnt) - mnt->mnt_ghosts;
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| 276 | return (mycount > count);
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| 277 | }
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| 278 |
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| 279 | |
| 280 | * check if the mount 'mnt' can be unmounted successfully.
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| 281 | * @mnt: the mount to be checked for unmount
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| 282 | * NOTE: unmounting 'mnt' would naturally propagate to all
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| 283 | * other mounts its parent propagates to.
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| 284 | * Check if any of these mounts that **do not have submounts**
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| 285 | * have more references than 'refcnt'. If so return busy.
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| 286 | *
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| 287 | * vfsmount lock must be held for write
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| 288 |
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| 289 | int propagate_mount_busy(struct mount *mnt, int refcnt)
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| 290 | {
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| 291 | struct mount *m, *child;
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| 292 | struct mount *parent = mnt->mnt_parent;
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| 293 | int ret = 0;
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| 294 |
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| 295 | if (mnt == parent)
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| 296 | return do_refcount_check(mnt, refcnt);
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| 297 |
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| 298 | |
| 299 | * quickly check if the current mount can be unmounted.
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| 300 | * If not, we don't have to go checking for all other
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| 301 | * mounts
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| 302 |
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| 303 | if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
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| 304 | return 1;
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| 305 |
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| 306 | for (m = propagation_next(parent, parent); m;
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| 307 | m = propagation_next(m, parent)) {
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| 308 | child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint, 0);
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| 309 | if (child && list_empty(&child->mnt_mounts) &&
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| 310 | (ret = do_refcount_check(child, 1)))
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| 311 | break;
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| 312 | }
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| 313 | return ret;
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| 314 | }
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| 315 |
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| 316 | |
| 317 | * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
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| 318 | * parent propagates to.
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| 319 |
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| 320 | static void __propagate_umount(struct mount *mnt)
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| 321 | {
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| 322 | struct mount *parent = mnt->mnt_parent;
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| 323 | struct mount *m;
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| 324 |
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| 325 | BUG_ON(parent == mnt);
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| 326 |
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| 327 | for (m = propagation_next(parent, parent); m;
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| 328 | m = propagation_next(m, parent)) {
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| 329 |
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| 330 | struct mount *child = __lookup_mnt(&m->mnt,
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| 331 | mnt->mnt_mountpoint, 0);
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| 332 | |
| 333 | * umount the child only if the child has no
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| 334 | * other children
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| 335 |
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| 336 | if (child && list_empty(&child->mnt_mounts))
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| 337 | list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
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| 338 | }
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| 339 | }
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| 340 |
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| 341 | |
| 342 | * collect all mounts that receive propagation from the mount in @list,
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| 343 | * and return these additional mounts in the same list.
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| 344 | * @list: the list of mounts to be unmounted.
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| 345 | *
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| 346 | * vfsmount lock must be held for write
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| 347 |
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| 348 | int propagate_umount(struct list_head *list)
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| 349 | {
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| 350 | struct mount *mnt;
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| 351 |
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| 352 | list_for_each_entry(mnt, list, mnt_hash)
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| 353 | __propagate_umount(mnt);
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| 354 | return 0;
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| 355 | }
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