/* -*- c -*- --------------------------------------------------------------- *
 *
 * linux/fs/autofs/expire.c
 *
 *  Copyright 1997-1998 Transmeta Corporation -- All Rights Reserved
 *  Copyright 1999-2000 Jeremy Fitzhardinge <jeremy@goop.org>
 *  Copyright 2001-2006 Ian Kent <raven@themaw.net>
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * ------------------------------------------------------------------------- */

#include "autofs_i.h"

static unsigned long now;

/* Check if a dentry can be expired */
static inline int autofs4_can_expire(struct dentry *dentry,
                                        unsigned long timeout, int do_now)
{
        struct autofs_info *ino = autofs4_dentry_ino(dentry);

        /* dentry in the process of being deleted */
        if (ino == NULL)
                return 0;

        if (!do_now) {
                /* Too young to die */
                if (!timeout || time_after(ino->last_used + timeout, now))
                        return 0;

                /* update last_used here :-
                   - obviously makes sense if it is in use now
                   - less obviously, prevents rapid-fire expire
                     attempts if expire fails the first time */
                ino->last_used = now;
        }
        return 1;
}

/* Check a mount point for busyness */
static int autofs4_mount_busy(struct vfsmount *mnt, struct dentry *dentry)
{
        struct dentry *top = dentry;
        struct path path = {.mnt = mnt, .dentry = dentry};
        int status = 1;

        DPRINTK("dentry %p %.*s",
                dentry, (int)dentry->d_name.len, dentry->d_name.name);

        path_get(&path);

        if (!follow_down_one(&path))
                goto done;

        if (is_autofs4_dentry(path.dentry)) {
                struct autofs_sb_info *sbi = autofs4_sbi(path.dentry->d_sb);

                /* This is an autofs submount, we can't expire it */
                if (autofs_type_indirect(sbi->type))
                        goto done;

                /*
                 * Otherwise it's an offset mount and we need to check
                 * if we can umount its mount, if there is one.
                 */
                if (!d_mountpoint(path.dentry)) {
                        status = 0;
                        goto done;
                }
        }

        /* Update the expiry counter if fs is busy */
        if (!may_umount_tree(path.mnt)) {
                struct autofs_info *ino = autofs4_dentry_ino(top);
                ino->last_used = jiffies;
                goto done;
        }

        status = 0;
done:
        DPRINTK("returning = %d", status);
        path_put(&path);
        return status;
}

/*
 * Calculate and dget next entry in top down tree traversal.
 */
static struct dentry *get_next_positive_dentry(struct dentry *prev,
                                                struct dentry *root)
{
        struct list_head *next;
        struct dentry *p, *ret;

        if (prev == NULL)
                return dget(root);

        spin_lock(&autofs4_lock);
relock:
        p = prev;
        spin_lock(&p->d_lock);
again:
        next = p->d_subdirs.next;
        if (next == &p->d_subdirs) {
                while (1) {
                        struct dentry *parent;

                        if (p == root) {
                                spin_unlock(&p->d_lock);
                                spin_unlock(&autofs4_lock);
                                dput(prev);
                                return NULL;
                        }

                        parent = p->d_parent;
                        if (!spin_trylock(&parent->d_lock)) {
                                spin_unlock(&p->d_lock);
                                cpu_relax();
                                goto relock;
                        }
                        spin_unlock(&p->d_lock);
                        next = p->d_u.d_child.next;
                        p = parent;
                        if (next != &parent->d_subdirs)
                                break;
                }
        }
        ret = list_entry(next, struct dentry, d_u.d_child);

        spin_lock_nested(&ret->d_lock, DENTRY_D_LOCK_NESTED);
        /* Negative dentry - try next */
        if (!simple_positive(ret)) {
                spin_unlock(&p->d_lock);
                p = ret;
                goto again;
        }
        dget_dlock(ret);
        spin_unlock(&ret->d_lock);
        spin_unlock(&p->d_lock);
        spin_unlock(&autofs4_lock);

        dput(prev);

        return ret;
}

/*
 * Check a direct mount point for busyness.
 * Direct mounts have similar expiry semantics to tree mounts.
 * The tree is not busy iff no mountpoints are busy and there are no
 * autofs submounts.
 */
static int autofs4_direct_busy(struct vfsmount *mnt,
                                struct dentry *top,
                                unsigned long timeout,
                                int do_now)
{
        DPRINTK("top %p %.*s",
                top, (int) top->d_name.len, top->d_name.name);

        /* If it's busy update the expiry counters */
        if (!may_umount_tree(mnt)) {
                struct autofs_info *ino = autofs4_dentry_ino(top);
                if (ino)
                        ino->last_used = jiffies;
                return 1;
        }

        /* Timeout of a direct mount is determined by its top dentry */
        if (!autofs4_can_expire(top, timeout, do_now))
                return 1;

        return 0;
}

/* Check a directory tree of mount points for busyness
 * The tree is not busy iff no mountpoints are busy
 */
static int autofs4_tree_busy(struct vfsmount *mnt,
                             struct dentry *top,
                             unsigned long timeout,
                             int do_now)
{
        struct autofs_info *top_ino = autofs4_dentry_ino(top);
        struct dentry *p;

        DPRINTK("top %p %.*s",
                top, (int)top->d_name.len, top->d_name.name);

        /* Negative dentry - give up */
        if (!simple_positive(top))
                return 1;

        p = NULL;
        while ((p = get_next_positive_dentry(p, top))) {
                DPRINTK("dentry %p %.*s",
                        p, (int) p->d_name.len, p->d_name.name);

                /*
                 * Is someone visiting anywhere in the subtree ?
                 * If there's no mount we need to check the usage
                 * count for the autofs dentry.
                 * If the fs is busy update the expiry counter.
                 */
                if (d_mountpoint(p)) {
                        if (autofs4_mount_busy(mnt, p)) {
                                top_ino->last_used = jiffies;
                                dput(p);
                                return 1;
                        }
                } else {
                        struct autofs_info *ino = autofs4_dentry_ino(p);
                        unsigned int ino_count = atomic_read(&ino->count);

                        /*
                         * Clean stale dentries below that have not been
                         * invalidated after a mount fail during lookup
                         */
                        d_invalidate(p);

                        /* allow for dget above and top is already dgot */
                        if (p == top)
                                ino_count += 2;
                        else
                                ino_count++;

                        if (p->d_count > ino_count) {
                                top_ino->last_used = jiffies;
                                dput(p);
                                return 1;
                        }
                }
        }

        /* Timeout of a tree mount is ultimately determined by its top dentry */
        if (!autofs4_can_expire(top, timeout, do_now))
                return 1;

        return 0;
}

static struct dentry *autofs4_check_leaves(struct vfsmount *mnt,
                                           struct dentry *parent,
                                           unsigned long timeout,
                                           int do_now)
{
        struct dentry *p;

        DPRINTK("parent %p %.*s",
                parent, (int)parent->d_name.len, parent->d_name.name);

        p = NULL;
        while ((p = get_next_positive_dentry(p, parent))) {
                DPRINTK("dentry %p %.*s",
                        p, (int) p->d_name.len, p->d_name.name);

                if (d_mountpoint(p)) {
                        /* Can we umount this guy */
                        if (autofs4_mount_busy(mnt, p))
                                continue;

                        /* Can we expire this guy */
                        if (autofs4_can_expire(p, timeout, do_now))
                                return p;
                }
        }
        return NULL;
}

/* Check if we can expire a direct mount (possibly a tree) */
struct dentry *autofs4_expire_direct(struct super_block *sb,
                                     struct vfsmount *mnt,
                                     struct autofs_sb_info *sbi,
                                     int how)
{
        unsigned long timeout;
        struct dentry *root = dget(sb->s_root);
        int do_now = how & AUTOFS_EXP_IMMEDIATE;
        struct autofs_info *ino;

        if (!root)
                return NULL;

        now = jiffies;
        timeout = sbi->exp_timeout;

        spin_lock(&sbi->fs_lock);
        ino = autofs4_dentry_ino(root);
        /* No point expiring a pending mount */
        if (ino->flags & AUTOFS_INF_PENDING) {
                spin_unlock(&sbi->fs_lock);
                return NULL;
        }
        managed_dentry_set_transit(root);
        if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {
                struct autofs_info *ino = autofs4_dentry_ino(root);
                ino->flags |= AUTOFS_INF_EXPIRING;
                init_completion(&ino->expire_complete);
                spin_unlock(&sbi->fs_lock);
                return root;
        }
        managed_dentry_clear_transit(root);
        spin_unlock(&sbi->fs_lock);
        dput(root);

        return NULL;
}

/*
 * Find an eligible tree to time-out
 * A tree is eligible if :-
 *  - it is unused by any user process
 *  - it has been unused for exp_timeout time
 */
struct dentry *autofs4_expire_indirect(struct super_block *sb,
                                       struct vfsmount *mnt,
                                       struct autofs_sb_info *sbi,
                                       int how)
{
        unsigned long timeout;
        struct dentry *root = sb->s_root;
        struct dentry *dentry;
        struct dentry *expired = NULL;
        int do_now = how & AUTOFS_EXP_IMMEDIATE;
        int exp_leaves = how & AUTOFS_EXP_LEAVES;
        struct autofs_info *ino;
        unsigned int ino_count;

        if (!root)
                return NULL;

        now = jiffies;
        timeout = sbi->exp_timeout;

        dentry = NULL;
        while ((dentry = get_next_positive_dentry(dentry, root))) {
                spin_lock(&sbi->fs_lock);
                ino = autofs4_dentry_ino(dentry);
                /* No point expiring a pending mount */
                if (ino->flags & AUTOFS_INF_PENDING)
                        goto cont;
                managed_dentry_set_transit(dentry);

                /*
                 * Case 1: (i) indirect mount or top level pseudo direct mount
                 *         (autofs-4.1).
                 *         (ii) indirect mount with offset mount, check the "/"
                 *         offset (autofs-5.0+).
                 */
                if (d_mountpoint(dentry)) {
                        DPRINTK("checking mountpoint %p %.*s",
                                dentry, (int)dentry->d_name.len, dentry->d_name.name);

                        /* Path walk currently on this dentry? */
                        ino_count = atomic_read(&ino->count) + 2;
                        if (dentry->d_count > ino_count)
                                goto next;

                        /* Can we umount this guy */
                        if (autofs4_mount_busy(mnt, dentry))
                                goto next;

                        /* Can we expire this guy */
                        if (autofs4_can_expire(dentry, timeout, do_now)) {
                                expired = dentry;
                                goto found;
                        }
                        goto next;
                }

                if (simple_empty(dentry))
                        goto next;

                /* Case 2: tree mount, expire iff entire tree is not busy */
                if (!exp_leaves) {
                        /* Path walk currently on this dentry? */
                        ino_count = atomic_read(&ino->count) + 1;
                        if (dentry->d_count > ino_count)
                                goto next;

                        if (!autofs4_tree_busy(mnt, dentry, timeout, do_now)) {
                                expired = dentry;
                                goto found;
                        }
                /*
                 * Case 3: pseudo direct mount, expire individual leaves
                 *         (autofs-4.1).
                 */
                } else {
                        /* Path walk currently on this dentry? */
                        ino_count = atomic_read(&ino->count) + 1;
                        if (dentry->d_count > ino_count)
                                goto next;

                        expired = autofs4_check_leaves(mnt, dentry, timeout, do_now);
                        if (expired) {
                                dput(dentry);
                                goto found;
                        }
                }
next:
                managed_dentry_clear_transit(dentry);
cont:
                spin_unlock(&sbi->fs_lock);
        }
        return NULL;

found:
        DPRINTK("returning %p %.*s",
                expired, (int)expired->d_name.len, expired->d_name.name);
        ino = autofs4_dentry_ino(expired);
        ino->flags |= AUTOFS_INF_EXPIRING;
        init_completion(&ino->expire_complete);
        spin_unlock(&sbi->fs_lock);
        spin_lock(&autofs4_lock);
        spin_lock(&expired->d_parent->d_lock);
        spin_lock_nested(&expired->d_lock, DENTRY_D_LOCK_NESTED);
        list_move(&expired->d_parent->d_subdirs, &expired->d_u.d_child);
        spin_unlock(&expired->d_lock);
        spin_unlock(&expired->d_parent->d_lock);
        spin_unlock(&autofs4_lock);
        return expired;
}

int autofs4_expire_wait(struct dentry *dentry)
{
        struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
        struct autofs_info *ino = autofs4_dentry_ino(dentry);
        int status;

        /* Block on any pending expire */
        spin_lock(&sbi->fs_lock);
        if (ino->flags & AUTOFS_INF_EXPIRING) {
                spin_unlock(&sbi->fs_lock);

                DPRINTK("waiting for expire %p name=%.*s",
                         dentry, dentry->d_name.len, dentry->d_name.name);

                status = autofs4_wait(sbi, dentry, NFY_NONE);
                wait_for_completion(&ino->expire_complete);

                DPRINTK("expire done status=%d", status);

                if (d_unhashed(dentry))
                        return -EAGAIN;

                return status;
        }
        spin_unlock(&sbi->fs_lock);

        return 0;
}

/* Perform an expiry operation */
int autofs4_expire_run(struct super_block *sb,
                      struct vfsmount *mnt,
                      struct autofs_sb_info *sbi,
                      struct autofs_packet_expire __user *pkt_p)
{
        struct autofs_packet_expire pkt;
        struct autofs_info *ino;
        struct dentry *dentry;
        int ret = 0;

        memset(&pkt,0,sizeof pkt);

        pkt.hdr.proto_version = sbi->version;
        pkt.hdr.type = autofs_ptype_expire;

        if ((dentry = autofs4_expire_indirect(sb, mnt, sbi, 0)) == NULL)
                return -EAGAIN;

        pkt.len = dentry->d_name.len;
        memcpy(pkt.name, dentry->d_name.name, pkt.len);
        pkt.name[pkt.len] = '\0';
        dput(dentry);

        if ( copy_to_user(pkt_p, &pkt, sizeof(struct autofs_packet_expire)) )
                ret = -EFAULT;

        spin_lock(&sbi->fs_lock);
        ino = autofs4_dentry_ino(dentry);
        ino->flags &= ~AUTOFS_INF_EXPIRING;
        if (!d_unhashed(dentry))
                managed_dentry_clear_transit(dentry);
        complete_all(&ino->expire_complete);
        spin_unlock(&sbi->fs_lock);

        return ret;
}

int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt,
                            struct autofs_sb_info *sbi, int when)
{
        struct dentry *dentry;
        int ret = -EAGAIN;

        if (autofs_type_trigger(sbi->type))
                dentry = autofs4_expire_direct(sb, mnt, sbi, when);
        else
                dentry = autofs4_expire_indirect(sb, mnt, sbi, when);

        if (dentry) {
                struct autofs_info *ino = autofs4_dentry_ino(dentry);

                /* This is synchronous because it makes the daemon a
                   little easier */
                ret = autofs4_wait(sbi, dentry, NFY_EXPIRE);

                spin_lock(&sbi->fs_lock);
                ino->flags &= ~AUTOFS_INF_EXPIRING;
                spin_lock(&dentry->d_lock);
                if (ret)
                        __managed_dentry_clear_transit(dentry);
                else {
                        if ((IS_ROOT(dentry) ||
                            (autofs_type_indirect(sbi->type) &&
                             IS_ROOT(dentry->d_parent))) &&
                            !(dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
                                __managed_dentry_set_automount(dentry);
                }
                spin_unlock(&dentry->d_lock);
                complete_all(&ino->expire_complete);
                spin_unlock(&sbi->fs_lock);
                dput(dentry);
        }

        return ret;
}

/* Call repeatedly until it returns -EAGAIN, meaning there's nothing
   more to be done */
int autofs4_expire_multi(struct super_block *sb, struct vfsmount *mnt,
                        struct autofs_sb_info *sbi, int __user *arg)
{
        int do_now = 0;

        if (arg && get_user(do_now, arg))
                return -EFAULT;

        return autofs4_do_expire_multi(sb, mnt, sbi, do_now);
}