pnode.c

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/*
 *  linux/fs/pnode.c
 *
 * (C) Copyright IBM Corporation 2005.
 *  Released under GPL v2.
 *  Author : Ram Pai ([email protected])
 *
 */
#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 mount *next_peer(struct mount *p)
{
    return list_entry(p->mnt_share.next, struct mount, mnt_share);
}

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

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

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

    do {
        /* Check the namespace first for optimization */
        if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.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 mount *mnt, const struct path *root)
{
    struct mount *m;

    for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
        struct mount *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 mount *mnt)
{
    struct mount *peer_mnt = mnt, *master = mnt->mnt_master;
    struct mount *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.mnt_root != mnt->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 mount, 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 mount *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.mnt_flags |= MNT_UNBINDABLE;
        else
            mnt->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 mount *propagation_next(struct mount *m,
                     struct mount *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 mount *master = m->mnt_master;

        if (master == origin->mnt_master) {
            struct mount *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 mount *get_source(struct mount *dest,
                struct mount *last_dest,
                struct mount *last_src,
                int *type)
{
    struct mount *p_last_src = NULL;
    struct mount *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 mount *dest_mnt, struct dentry *dest_dentry,
            struct mount *source_mnt, struct list_head *tree_list)
{
    struct mount *m, *child;
    int ret = 0;
    struct mount *prev_dest_mnt = dest_mnt;
    struct mount *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 mount *source;

        if (IS_MNT_NEW(m))
            continue;

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

        child = copy_tree(source, source->mnt.mnt_root, type);
        if (IS_ERR(child)) {
            ret = PTR_ERR(child);
            list_splice(tree_list, tmp_list.prev);
            goto out;
        }

        if (is_subdir(dest_dentry, m->mnt.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 mount, 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 mount *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 mount *mnt, int refcnt)
{
    struct mount *m, *child;
    struct mount *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->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 mount *mnt)
{
    struct mount *parent = mnt->mnt_parent;
    struct mount *m;

    BUG_ON(parent == mnt);

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

        struct mount *child = __lookup_mnt(&m->mnt,
                    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 mount *mnt;

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