![Miklos Szeredi](/assets/img/avatar_default.png)
Add a unique ID to each peer group using the IDR infrastructure. The identifiers are reused after the peer group dissolves. The IDR structures are protected by holding namepspace_sem for write while allocating or deallocating IDs. IDs are allocated when a previously unshared vfsmount becomes the first member of a peer group. When a new member is added to an existing group, the ID is copied from one of the old members. IDs are freed when the last member of a peer group is unshared. Setting the MNT_SHARED flag on members of a subtree is done as a separate step, after all the IDs have been allocated. This way an allocation failure can be cleaned up easilty, without affecting the propagation state. Based on design sketch by Al Viro. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
308 lines
7.7 KiB
C
308 lines
7.7 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 "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 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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static inline struct vfsmount *first_slave(struct vfsmount *p)
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{
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return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
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}
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static inline struct vfsmount *next_slave(struct vfsmount *p)
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{
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return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
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}
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static int do_make_slave(struct vfsmount *mnt)
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{
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struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
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struct vfsmount *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 than
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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_root != 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 (IS_MNT_SHARED(mnt) && 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 vfsmount, 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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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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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_flags |= MNT_UNBINDABLE;
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else
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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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static struct vfsmount *propagation_next(struct vfsmount *m,
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struct vfsmount *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 vfsmount *next;
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struct vfsmount *master = m->mnt_master;
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if (master == origin->mnt_master) {
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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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/*
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* return the source mount to be used for cloning
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*
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* @dest the current destination mount
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* @last_dest the last seen destination mount
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* @last_src the last seen source mount
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* @type return CL_SLAVE if the new mount has to be
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* cloned as a slave.
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*/
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static struct vfsmount *get_source(struct vfsmount *dest,
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struct vfsmount *last_dest,
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struct vfsmount *last_src,
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int *type)
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{
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struct vfsmount *p_last_src = NULL;
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struct vfsmount *p_last_dest = NULL;
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*type = CL_PROPAGATION;
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if (IS_MNT_SHARED(dest))
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*type |= CL_MAKE_SHARED;
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while (last_dest != dest->mnt_master) {
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p_last_dest = last_dest;
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p_last_src = last_src;
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last_dest = last_dest->mnt_master;
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last_src = last_src->mnt_master;
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}
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if (p_last_dest) {
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do {
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p_last_dest = next_peer(p_last_dest);
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} while (IS_MNT_NEW(p_last_dest));
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}
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if (dest != p_last_dest) {
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*type |= CL_SLAVE;
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return last_src;
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} else
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return p_last_src;
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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;
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struct vfsmount *source;
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if (IS_MNT_NEW(m))
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continue;
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source = get_source(m, prev_dest_mnt, prev_src_mnt, &type);
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if (!(child = copy_tree(source, source->mnt_root, 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_first_entry(&tmp_list, struct vfsmount, 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) - mnt->mnt_ghosts;
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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_move_tail(&child->mnt_hash, &mnt->mnt_hash);
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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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