pnode.c 4.82 KB
Newer Older
1 2 3 4 5 6 7 8 9 10 11 12 13
/*
 *  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"

Ram Pai's avatar
Ram Pai committed
14 15 16 17 18 19
/* 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);
}

20 21
void change_mnt_propagation(struct vfsmount *mnt, int type)
{
Ram Pai's avatar
Ram Pai committed
22
	if (type == MS_SHARED) {
23
		set_mnt_shared(mnt);
Ram Pai's avatar
Ram Pai committed
24 25 26 27
	} else {
		list_del_init(&mnt->mnt_share);
		mnt->mnt_flags &= ~MNT_PNODE_MASK;
	}
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

/*
 * 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);
102
		umount_tree(child, 0, &umount_list);
103 104 105 106 107
	}
	spin_unlock(&vfsmount_lock);
	release_mounts(&umount_list);
	return ret;
}
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

/*
 * 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;
}