An unmount of a mount creates a umount event on the parent. If the parent is a shared mount, it gets propagated to all mounts in the peer group. 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>
193 lines
4.8 KiB
C
193 lines
4.8 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/namespace.h>
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#include <linux/mount.h>
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#include <linux/fs.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 vfsmount *next_peer(struct vfsmount *p)
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{
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return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
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}
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void change_mnt_propagation(struct vfsmount *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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} else {
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list_del_init(&mnt->mnt_share);
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mnt->mnt_flags &= ~MNT_PNODE_MASK;
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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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static struct vfsmount *propagation_next(struct vfsmount *m,
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struct vfsmount *origin)
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{
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m = next_peer(m);
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if (m == origin)
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return NULL;
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return m;
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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 vfsmount *dest_mnt, struct dentry *dest_dentry,
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struct vfsmount *source_mnt, struct list_head *tree_list)
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{
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struct vfsmount *m, *child;
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int ret = 0;
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struct vfsmount *prev_dest_mnt = dest_mnt;
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struct vfsmount *prev_src_mnt = source_mnt;
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LIST_HEAD(tmp_list);
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LIST_HEAD(umount_list);
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for (m = propagation_next(dest_mnt, dest_mnt); m;
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m = propagation_next(m, dest_mnt)) {
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int type = CL_PROPAGATION;
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if (IS_MNT_NEW(m))
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continue;
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if (IS_MNT_SHARED(m))
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type |= CL_MAKE_SHARED;
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if (!(child = copy_tree(source_mnt, source_mnt->mnt_root,
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type))) {
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ret = -ENOMEM;
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list_splice(tree_list, tmp_list.prev);
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goto out;
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}
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if (is_subdir(dest_dentry, m->mnt_root)) {
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mnt_set_mountpoint(m, dest_dentry, child);
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list_add_tail(&child->mnt_hash, tree_list);
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} else {
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/*
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* This can happen if the parent mount was bind mounted
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* on some subdirectory of a shared/slave mount.
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*/
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list_add_tail(&child->mnt_hash, &tmp_list);
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}
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prev_dest_mnt = m;
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prev_src_mnt = child;
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}
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out:
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spin_lock(&vfsmount_lock);
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while (!list_empty(&tmp_list)) {
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child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
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list_del_init(&child->mnt_hash);
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umount_tree(child, 0, &umount_list);
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}
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spin_unlock(&vfsmount_lock);
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release_mounts(&umount_list);
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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 vfsmount *mnt, int count)
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{
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int mycount = atomic_read(&mnt->mnt_count);
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return (mycount > 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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int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
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{
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struct vfsmount *m, *child;
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struct vfsmount *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(m, mnt->mnt_mountpoint, 0);
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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 vfsmount *mnt)
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{
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struct vfsmount *parent = mnt->mnt_parent;
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struct vfsmount *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 vfsmount *child = __lookup_mnt(m,
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mnt->mnt_mountpoint, 0);
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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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list_del(&child->mnt_hash);
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list_add_tail(&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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int propagate_umount(struct list_head *list)
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{
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struct vfsmount *mnt;
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list_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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