summaryrefslogtreecommitdiffstats
path: root/fs/pnode.c
blob: 7bc942d047cd299df0e76282664ba1d052c81c1b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
/*
 *  linux/fs/pnode.c
 *
 * (C) Copyright IBM Corporation 2005.
 *	Released under GPL v2.
 *	Author : Ram Pai (linuxram@us.ibm.com)
 *
 */
#include <linux/namespace.h>
#include <linux/mount.h>
#include <linux/fs.h>
#include "pnode.h"

/* return the next shared peer mount of @p */
static inline struct vfsmount *next_peer(struct vfsmount *p)
{
	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
}

void change_mnt_propagation(struct vfsmount *mnt, int type)
{
	if (type == MS_SHARED) {
		set_mnt_shared(mnt);
	} else {
		list_del_init(&mnt->mnt_share);
		mnt->mnt_flags &= ~MNT_PNODE_MASK;
	}
}

/*
 * get the next mount in the propagation tree.
 * @m: the mount seen last
 * @origin: the original mount from where the tree walk initiated
 */
static struct vfsmount *propagation_next(struct vfsmount *m,
					 struct vfsmount *origin)
{
	m = next_peer(m);
	if (m == origin)
		return NULL;
	return m;
}

/*
 * mount 'source_mnt' under the destination 'dest_mnt' at
 * dentry 'dest_dentry'. And propagate that mount to
 * all the peer and slave mounts of 'dest_mnt'.
 * Link all the new mounts into a propagation tree headed at
 * source_mnt. Also link all the new mounts using ->mnt_list
 * headed at source_mnt's ->mnt_list
 *
 * @dest_mnt: destination mount.
 * @dest_dentry: destination dentry.
 * @source_mnt: source mount.
 * @tree_list : list of heads of trees to be attached.
 */
int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
		    struct vfsmount *source_mnt, struct list_head *tree_list)
{
	struct vfsmount *m, *child;
	int ret = 0;
	struct vfsmount *prev_dest_mnt = dest_mnt;
	struct vfsmount *prev_src_mnt  = source_mnt;
	LIST_HEAD(tmp_list);
	LIST_HEAD(umount_list);

	for (m = propagation_next(dest_mnt, dest_mnt); m;
			m = propagation_next(m, dest_mnt)) {
		int type = CL_PROPAGATION;

		if (IS_MNT_NEW(m))
			continue;

		if (IS_MNT_SHARED(m))
			type |= CL_MAKE_SHARED;

		if (!(child = copy_tree(source_mnt, source_mnt->mnt_root,
						type))) {
			ret = -ENOMEM;
			list_splice(tree_list, tmp_list.prev);
			goto out;
		}

		if (is_subdir(dest_dentry, m->mnt_root)) {
			mnt_set_mountpoint(m, dest_dentry, child);
			list_add_tail(&child->mnt_hash, tree_list);
		} else {
			/*
			 * This can happen if the parent mount was bind mounted
			 * on some subdirectory of a shared/slave mount.
			 */
			list_add_tail(&child->mnt_hash, &tmp_list);
		}
		prev_dest_mnt = m;
		prev_src_mnt  = child;
	}
out:
	spin_lock(&vfsmount_lock);
	while (!list_empty(&tmp_list)) {
		child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
		list_del_init(&child->mnt_hash);
		umount_tree(child, 0, &umount_list);
	}
	spin_unlock(&vfsmount_lock);
	release_mounts(&umount_list);
	return ret;
}

/*
 * return true if the refcount is greater than count
 */
static inline int do_refcount_check(struct vfsmount *mnt, int count)
{
	int mycount = atomic_read(&mnt->mnt_count);
	return (mycount > count);
}

/*
 * check if the mount 'mnt' can be unmounted successfully.
 * @mnt: the mount to be checked for unmount
 * NOTE: unmounting 'mnt' would naturally propagate to all
 * other mounts its parent propagates to.
 * Check if any of these mounts that **do not have submounts**
 * have more references than 'refcnt'. If so return busy.
 */
int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
{
	struct vfsmount *m, *child;
	struct vfsmount *parent = mnt->mnt_parent;
	int ret = 0;

	if (mnt == parent)
		return do_refcount_check(mnt, refcnt);

	/*
	 * quickly check if the current mount can be unmounted.
	 * If not, we don't have to go checking for all other
	 * mounts
	 */
	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
		return 1;

	for (m = propagation_next(parent, parent); m;
	     		m = propagation_next(m, parent)) {
		child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
		if (child && list_empty(&child->mnt_mounts) &&
		    (ret = do_refcount_check(child, 1)))
			break;
	}
	return ret;
}

/*
 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 * parent propagates to.
 */
static void __propagate_umount(struct vfsmount *mnt)
{
	struct vfsmount *parent = mnt->mnt_parent;
	struct vfsmount *m;

	BUG_ON(parent == mnt);

	for (m = propagation_next(parent, parent); m;
			m = propagation_next(m, parent)) {

		struct vfsmount *child = __lookup_mnt(m,
					mnt->mnt_mountpoint, 0);
		/*
		 * umount the child only if the child has no
		 * other children
		 */
		if (child && list_empty(&child->mnt_mounts)) {
			list_del(&child->mnt_hash);
			list_add_tail(&child->mnt_hash, &mnt->mnt_hash);
		}
	}
}

/*
 * collect all mounts that receive propagation from the mount in @list,
 * and return these additional mounts in the same list.
 * @list: the list of mounts to be unmounted.
 */
int propagate_umount(struct list_head *list)
{
	struct vfsmount *mnt;

	list_for_each_entry(mnt, list, mnt_hash)
		__propagate_umount(mnt);
	return 0;
}
OpenPOWER on IntegriCloud