expire.c

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/* -*- c -*- --------------------------------------------------------------- *
 *
 * linux/fs/autofs/expire.c
 *
 *  Copyright 1997-1998 Transmeta Corporation -- All Rights Reserved
 *  Copyright 1999-2000 Jeremy Fitzhardinge <[email protected]>
 *  Copyright 2001-2006 Ian Kent <[email protected]>
 *
 * 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 the subdirs list under root.
 */
static struct dentry *get_next_positive_subdir(struct dentry *prev,
                        struct dentry *root)
{
    struct autofs_sb_info *sbi = autofs4_sbi(root->d_sb);
    struct list_head *next;
    struct dentry *q;

    spin_lock(&sbi->lookup_lock);
    spin_lock(&root->d_lock);

    if (prev)
        next = prev->d_u.d_child.next;
    else {
        prev = dget_dlock(root);
        next = prev->d_subdirs.next;
    }

cont:
    if (next == &root->d_subdirs) {
        spin_unlock(&root->d_lock);
        spin_unlock(&sbi->lookup_lock);
        dput(prev);
        return NULL;
    }

    q = list_entry(next, struct dentry, d_u.d_child);

    spin_lock_nested(&q->d_lock, DENTRY_D_LOCK_NESTED);
    /* Already gone or negative dentry (under construction) - try next */
    if (q->d_count == 0 || !simple_positive(q)) {
        spin_unlock(&q->d_lock);
        next = q->d_u.d_child.next;
        goto cont;
    }
    dget_dlock(q);
    spin_unlock(&q->d_lock);
    spin_unlock(&root->d_lock);
    spin_unlock(&sbi->lookup_lock);

    dput(prev);

    return q;
}

/*
 * Calculate and dget next entry in top down tree traversal.
 */
static struct dentry *get_next_positive_dentry(struct dentry *prev,
                        struct dentry *root)
{
    struct autofs_sb_info *sbi = autofs4_sbi(root->d_sb);
    struct list_head *next;
    struct dentry *p, *ret;

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

    spin_lock(&sbi->lookup_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(&sbi->lookup_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);
        lock_set_subclass(&ret->d_lock.dep_map, 0, _RET_IP_);
        p = ret;
        goto again;
    }
    dget_dlock(ret);
    spin_unlock(&ret->d_lock);
    spin_unlock(&p->d_lock);
    spin_unlock(&sbi->lookup_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)
        goto out;
    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;
    }
out:
    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_subdir(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 next;

        /*
         * 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);

            /* 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:
        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(&sbi->lookup_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(&sbi->lookup_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;
    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) {
            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);
}