/*
 *  linux/fs/pnode.c
 *
 * (C) Copyright IBM Corporation 2005.
 *      Released under GPL v2.
 *      Author : Ram Pai (linuxram@us.ibm.com)
 *
 */
#include <linux/mnt_namespace.h>
#include <linux/mount.h>
#include <linux/fs.h>
#include "internal.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);
}

static inline struct vfsmount *first_slave(struct vfsmount *p)
{
        return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
}

static inline struct vfsmount *next_slave(struct vfsmount *p)
{
        return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
}

/*
 * Return true if path is reachable from root
 *
 * namespace_sem is held, and mnt is attached
 */
static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
                         const struct path *root)
{
        while (mnt != root->mnt && mnt->mnt_parent != mnt) {
                dentry = mnt->mnt_mountpoint;
                mnt = mnt->mnt_parent;
        }
        return mnt == root->mnt && is_subdir(dentry, root->dentry);
}

static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
                                            struct mnt_namespace *ns,
                                            const struct path *root)
{
        struct vfsmount *m = mnt;

        do {
                /* Check the namespace first for optimization */
                if (m->mnt_ns == ns && is_path_reachable(m, m->mnt_root, root))
                        return m;

                m = next_peer(m);
        } while (m != mnt);

        return NULL;
}

/*
 * Get ID of closest dominating peer group having a representative
 * under the given root.
 *
 * Caller must hold namespace_sem
 */
int get_dominating_id(struct vfsmount *mnt, const struct path *root)
{
        struct vfsmount *m;

        for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
                struct vfsmount *d = get_peer_under_root(m, mnt->mnt_ns, root);
                if (d)
                        return d->mnt_group_id;
        }

        return 0;
}

static int do_make_slave(struct vfsmount *mnt)
{
        struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
        struct vfsmount *slave_mnt;

        /*
         * slave 'mnt' to a peer mount that has the
         * same root dentry. If none is available then
         * slave it to anything that is available.
         */
        while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
               peer_mnt->mnt_root != mnt->mnt_root) ;

        if (peer_mnt == mnt) {
                peer_mnt = next_peer(mnt);
                if (peer_mnt == mnt)
                        peer_mnt = NULL;
        }
        if (IS_MNT_SHARED(mnt) && list_empty(&mnt->mnt_share))
                mnt_release_group_id(mnt);

        list_del_init(&mnt->mnt_share);
        mnt->mnt_group_id = 0;

        if (peer_mnt)
                master = peer_mnt;

        if (master) {
                list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
                        slave_mnt->mnt_master = master;
                list_move(&mnt->mnt_slave, &master->mnt_slave_list);
                list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
                INIT_LIST_HEAD(&mnt->mnt_slave_list);
        } else {
                struct list_head *p = &mnt->mnt_slave_list;
                while (!list_empty(p)) {
                        slave_mnt = list_first_entry(p,
                                        struct vfsmount, mnt_slave);
                        list_del_init(&slave_mnt->mnt_slave);
                        slave_mnt->mnt_master = NULL;
                }
        }
        mnt->mnt_master = master;
        CLEAR_MNT_SHARED(mnt);
        return 0;
}

/*
 * vfsmount lock must be held for write
 */
void change_mnt_propagation(struct vfsmount *mnt, int type)
{
        if (type == MS_SHARED) {
                set_mnt_shared(mnt);
                return;
        }
        do_make_slave(mnt);
        if (type != MS_SLAVE) {
                list_del_init(&mnt->mnt_slave);
                mnt->mnt_master = NULL;
                if (type == MS_UNBINDABLE)
                        mnt->mnt_flags |= MNT_UNBINDABLE;
                else
                        mnt->mnt_flags &= ~MNT_UNBINDABLE;
        }
}

/*
 * get the next mount in the propagation tree.
 * @m: the mount seen last
 * @origin: the original mount from where the tree walk initiated
 *
 * Note that peer groups form contiguous segments of slave lists.
 * We rely on that in get_source() to be able to find out if
 * vfsmount found while iterating with propagation_next() is
 * a peer of one we'd found earlier.
 */
static struct vfsmount *propagation_next(struct vfsmount *m,
                                         struct vfsmount *origin)
{
        /* are there any slaves of this mount? */
        if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
                return first_slave(m);

        while (1) {
                struct vfsmount *next;
                struct vfsmount *master = m->mnt_master;

                if (master == origin->mnt_master) {
                        next = next_peer(m);
                        return ((next == origin) ? NULL : next);
                } else if (m->mnt_slave.next != &master->mnt_slave_list)
                        return next_slave(m);

                /* back at master */
                m = master;
        }
}

/*
 * return the source mount to be used for cloning
 *
 * @dest        the current destination mount
 * @last_dest   the last seen destination mount
 * @last_src    the last seen source mount
 * @type        return CL_SLAVE if the new mount has to be
 *              cloned as a slave.
 */
static struct vfsmount *get_source(struct vfsmount *dest,
                                        struct vfsmount *last_dest,
                                        struct vfsmount *last_src,
                                        int *type)
{
        struct vfsmount *p_last_src = NULL;
        struct vfsmount *p_last_dest = NULL;

        while (last_dest != dest->mnt_master) {
                p_last_dest = last_dest;
                p_last_src = last_src;
                last_dest = last_dest->mnt_master;
                last_src = last_src->mnt_master;
        }

        if (p_last_dest) {
                do {
                        p_last_dest = next_peer(p_last_dest);
                } while (IS_MNT_NEW(p_last_dest));
                /* is that a peer of the earlier? */
                if (dest == p_last_dest) {
                        *type = CL_MAKE_SHARED;
                        return p_last_src;
                }
        }
        /* slave of the earlier, then */
        *type = CL_SLAVE;
        /* beginning of peer group among the slaves? */
        if (IS_MNT_SHARED(dest))
                *type |= CL_MAKE_SHARED;
        return last_src;
}

/*
 * 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;
                struct vfsmount *source;

                if (IS_MNT_NEW(m))
                        continue;

                source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);

                if (!(child = copy_tree(source, source->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:
        br_write_lock(vfsmount_lock);
        while (!list_empty(&tmp_list)) {
                child = list_first_entry(&tmp_list, struct vfsmount, mnt_hash);
                umount_tree(child, 0, &umount_list);
        }
        br_write_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 = mnt_get_count(mnt) - mnt->mnt_ghosts;
        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.
 *
 * vfsmount lock must be held for write
 */
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_move_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.
 *
 * vfsmount lock must be held for write
 */
int propagate_umount(struct list_head *list)
{
        struct vfsmount *mnt;

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