autofs4: fix direct mount pending expire race - correction

[linux-2.6/mini2440.git] / fs / autofs4 / root.c

/* -*- c -*- --------------------------------------------------------------- *
 *
 * linux/fs/autofs/root.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 <linux/capability.h>
#include <linux/errno.h>
#include <linux/stat.h>
#include <linux/param.h>
#include <linux/time.h>
#include "autofs_i.h"

static int autofs4_dir_symlink(struct inode *,struct dentry *,const char *);
static int autofs4_dir_unlink(struct inode *,struct dentry *);
static int autofs4_dir_rmdir(struct inode *,struct dentry *);
static int autofs4_dir_mkdir(struct inode *,struct dentry *,int);
static int autofs4_root_ioctl(struct inode *, struct file *,unsigned int,unsigned long);
static int autofs4_dir_open(struct inode *inode, struct file *file);
static int autofs4_root_readdir(struct file * filp, void * dirent, filldir_t filldir);
static struct dentry *autofs4_lookup(struct inode *,struct dentry *, struct nameidata *);
static void *autofs4_follow_link(struct dentry *, struct nameidata *);

#define TRIGGER_FLAGS   (LOOKUP_CONTINUE | LOOKUP_DIRECTORY)
#define TRIGGER_INTENTS (LOOKUP_OPEN | LOOKUP_CREATE)

const struct file_operations autofs4_root_operations = {
        .open           = dcache_dir_open,
        .release        = dcache_dir_close,
        .read           = generic_read_dir,
        .readdir        = autofs4_root_readdir,
        .ioctl          = autofs4_root_ioctl,
};

const struct file_operations autofs4_dir_operations = {
        .open           = autofs4_dir_open,
        .release        = dcache_dir_close,
        .read           = generic_read_dir,
        .readdir        = dcache_readdir,
};

const struct inode_operations autofs4_indirect_root_inode_operations = {
        .lookup         = autofs4_lookup,
        .unlink         = autofs4_dir_unlink,
        .symlink        = autofs4_dir_symlink,
        .mkdir          = autofs4_dir_mkdir,
        .rmdir          = autofs4_dir_rmdir,
};

const struct inode_operations autofs4_direct_root_inode_operations = {
        .lookup         = autofs4_lookup,
        .unlink         = autofs4_dir_unlink,
        .mkdir          = autofs4_dir_mkdir,
        .rmdir          = autofs4_dir_rmdir,
        .follow_link    = autofs4_follow_link,
};

const struct inode_operations autofs4_dir_inode_operations = {
        .lookup         = autofs4_lookup,
        .unlink         = autofs4_dir_unlink,
        .symlink        = autofs4_dir_symlink,
        .mkdir          = autofs4_dir_mkdir,
        .rmdir          = autofs4_dir_rmdir,
};

static int autofs4_root_readdir(struct file *file, void *dirent,
                                filldir_t filldir)
{
        struct autofs_sb_info *sbi = autofs4_sbi(file->f_path.dentry->d_sb);
        int oz_mode = autofs4_oz_mode(sbi);

        DPRINTK("called, filp->f_pos = %lld", file->f_pos);

        /*
         * Don't set reghost flag if:
         * 1) f_pos is larger than zero -- we've already been here.
         * 2) we haven't even enabled reghosting in the 1st place.
         * 3) this is the daemon doing a readdir
         */
        if (oz_mode && file->f_pos == 0 && sbi->reghost_enabled)
                sbi->needs_reghost = 1;

        DPRINTK("needs_reghost = %d", sbi->needs_reghost);

        return dcache_readdir(file, dirent, filldir);
}

static int autofs4_dir_open(struct inode *inode, struct file *file)
{
        struct dentry *dentry = file->f_path.dentry;
        struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);

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

        if (autofs4_oz_mode(sbi))
                goto out;

        /*
         * An empty directory in an autofs file system is always a
         * mount point. The daemon must have failed to mount this
         * during lookup so it doesn't exist. This can happen, for
         * example, if user space returns an incorrect status for a
         * mount request. Otherwise we're doing a readdir on the
         * autofs file system so just let the libfs routines handle
         * it.
         */
        spin_lock(&dcache_lock);
        if (!d_mountpoint(dentry) && __simple_empty(dentry)) {
                spin_unlock(&dcache_lock);
                return -ENOENT;
        }
        spin_unlock(&dcache_lock);

out:
        return dcache_dir_open(inode, file);
}

static int try_to_fill_dentry(struct dentry *dentry, int flags)
{
        struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
        struct autofs_info *ino = autofs4_dentry_ino(dentry);
        int status;

        /* Block on any pending expiry here; invalidate the dentry
           when expiration is done to trigger mount request with a new
           dentry */
        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 the directory still exists the mount request must
                 * continue otherwise it can't be followed at the right
                 * time during the walk.
                 */
                status = d_invalidate(dentry);
                if (status != -EBUSY)
                        return -EAGAIN;

                goto cont;
        }
        spin_unlock(&sbi->fs_lock);
cont:
        DPRINTK("dentry=%p %.*s ino=%p",
                 dentry, dentry->d_name.len, dentry->d_name.name, dentry->d_inode);

        /*
         * Wait for a pending mount, triggering one if there
         * isn't one already
         */
        if (dentry->d_inode == NULL) {
                DPRINTK("waiting for mount name=%.*s",
                         dentry->d_name.len, dentry->d_name.name);

                status = autofs4_wait(sbi, dentry, NFY_MOUNT);

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

                /* Turn this into a real negative dentry? */
                if (status == -ENOENT) {
                        spin_lock(&dentry->d_lock);
                        dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
                        spin_unlock(&dentry->d_lock);
                        return status;
                } else if (status) {
                        /* Return a negative dentry, but leave it "pending" */
                        return status;
                }
        /* Trigger mount for path component or follow link */
        } else if (dentry->d_flags & DCACHE_AUTOFS_PENDING ||
                        flags & (TRIGGER_FLAGS | TRIGGER_INTENTS) ||
                        current->link_count) {
                DPRINTK("waiting for mount name=%.*s",
                        dentry->d_name.len, dentry->d_name.name);

                spin_lock(&dentry->d_lock);
                dentry->d_flags |= DCACHE_AUTOFS_PENDING;
                spin_unlock(&dentry->d_lock);
                status = autofs4_wait(sbi, dentry, NFY_MOUNT);

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

                if (status) {
                        spin_lock(&dentry->d_lock);
                        dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
                        spin_unlock(&dentry->d_lock);
                        return status;
                }
        }

        /* Initialize expiry counter after successful mount */
        if (ino)
                ino->last_used = jiffies;

        spin_lock(&dentry->d_lock);
        dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
        spin_unlock(&dentry->d_lock);

        return 0;
}

/* For autofs direct mounts the follow link triggers the mount */
static void *autofs4_follow_link(struct dentry *dentry, struct nameidata *nd)
{
        struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);
        struct autofs_info *ino = autofs4_dentry_ino(dentry);
        int oz_mode = autofs4_oz_mode(sbi);
        unsigned int lookup_type;
        int status;

        DPRINTK("dentry=%p %.*s oz_mode=%d nd->flags=%d",
                dentry, dentry->d_name.len, dentry->d_name.name, oz_mode,
                nd->flags);
        /*
         * For an expire of a covered direct or offset mount we need
         * to beeak out of follow_down() at the autofs mount trigger
         * (d_mounted--), so we can see the expiring flag, and manage
         * the blocking and following here until the expire is completed.
         */
        if (oz_mode) {
                spin_lock(&sbi->fs_lock);
                if (ino->flags & AUTOFS_INF_EXPIRING) {
                        spin_unlock(&sbi->fs_lock);
                        /* Follow down to our covering mount. */
                        if (!follow_down(&nd->path.mnt, &nd->path.dentry))
                                goto done;
                        goto follow;
                }
                spin_unlock(&sbi->fs_lock);
                goto done;
        }

        /* If an expire request is pending everyone must wait. */
        spin_lock(&sbi->fs_lock);
        if (ino->flags & AUTOFS_INF_EXPIRING) {
                spin_unlock(&sbi->fs_lock);

                DPRINTK("waiting for active request %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("request done status=%d", status);

                goto cont;
        }
        spin_unlock(&sbi->fs_lock);
cont:
        /* We trigger a mount for almost all flags */
        lookup_type = nd->flags & (TRIGGER_FLAGS | TRIGGER_INTENTS);
        if (!(lookup_type || dentry->d_flags & DCACHE_AUTOFS_PENDING))
                goto follow;

        /*
         * If the dentry contains directories then it is an autofs
         * multi-mount with no root mount offset. So don't try to
         * mount it again.
         */
        spin_lock(&dcache_lock);
        if (dentry->d_flags & DCACHE_AUTOFS_PENDING ||
            (!d_mountpoint(dentry) && __simple_empty(dentry))) {
                spin_unlock(&dcache_lock);

                status = try_to_fill_dentry(dentry, 0);
                if (status)
                        goto out_error;

                goto follow;
        }
        spin_unlock(&dcache_lock);
follow:
        /*
         * If there is no root mount it must be an autofs
         * multi-mount with no root offset so we don't need
         * to follow it.
         */
        if (d_mountpoint(dentry)) {
                if (!autofs4_follow_mount(&nd->path.mnt,
                                          &nd->path.dentry)) {
                        status = -ENOENT;
                        goto out_error;
                }
        }

done:
        return NULL;

out_error:
        path_put(&nd->path);
        return ERR_PTR(status);
}

/*
 * Revalidate is called on every cache lookup.  Some of those
 * cache lookups may actually happen while the dentry is not
 * yet completely filled in, and revalidate has to delay such
 * lookups..
 */
static int autofs4_revalidate(struct dentry *dentry, struct nameidata *nd)
{
        struct inode *dir = dentry->d_parent->d_inode;
        struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
        int oz_mode = autofs4_oz_mode(sbi);
        int flags = nd ? nd->flags : 0;
        int status = 1;

        /* Pending dentry */
        spin_lock(&sbi->fs_lock);
        if (autofs4_ispending(dentry)) {
                /* The daemon never causes a mount to trigger */
                spin_unlock(&sbi->fs_lock);

                if (oz_mode)
                        return 1;

                /*
                 * A zero status is success otherwise we have a
                 * negative error code.
                 */
                status = try_to_fill_dentry(dentry, flags);
                if (status == 0)
                        return 1;

                /*
                 * A status of EAGAIN here means that the dentry has gone
                 * away while waiting for an expire to complete. If we are
                 * racing with expire lookup will wait for it so this must
                 * be a revalidate and we need to send it to lookup.
                 */
                if (status == -EAGAIN)
                        return 0;

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

        /* Negative dentry.. invalidate if "old" */
        if (dentry->d_inode == NULL)
                return 0;

        /* Check for a non-mountpoint directory with no contents */
        spin_lock(&dcache_lock);
        if (S_ISDIR(dentry->d_inode->i_mode) &&
            !d_mountpoint(dentry) && 
            __simple_empty(dentry)) {
                DPRINTK("dentry=%p %.*s, emptydir",
                         dentry, dentry->d_name.len, dentry->d_name.name);
                spin_unlock(&dcache_lock);

                /* The daemon never causes a mount to trigger */
                if (oz_mode)
                        return 1;

                /*
                 * A zero status is success otherwise we have a
                 * negative error code.
                 */
                status = try_to_fill_dentry(dentry, flags);
                if (status == 0)
                        return 1;

                return status;
        }
        spin_unlock(&dcache_lock);

        return 1;
}

void autofs4_dentry_release(struct dentry *de)
{
        struct autofs_info *inf;

        DPRINTK("releasing %p", de);

        inf = autofs4_dentry_ino(de);
        de->d_fsdata = NULL;

        if (inf) {
                struct autofs_sb_info *sbi = autofs4_sbi(de->d_sb);

                if (sbi) {
                        spin_lock(&sbi->lookup_lock);
                        if (!list_empty(&inf->active))
                                list_del(&inf->active);
                        if (!list_empty(&inf->expiring))
                                list_del(&inf->expiring);
                        spin_unlock(&sbi->lookup_lock);
                }

                inf->dentry = NULL;
                inf->inode = NULL;

                autofs4_free_ino(inf);
        }
}

/* For dentries of directories in the root dir */
static struct dentry_operations autofs4_root_dentry_operations = {
        .d_revalidate   = autofs4_revalidate,
        .d_release      = autofs4_dentry_release,
};

/* For other dentries */
static struct dentry_operations autofs4_dentry_operations = {
        .d_revalidate   = autofs4_revalidate,
        .d_release      = autofs4_dentry_release,
};

static struct dentry *autofs4_lookup_active(struct autofs_sb_info *sbi, struct dentry *parent, struct qstr *name)
{
        unsigned int len = name->len;
        unsigned int hash = name->hash;
        const unsigned char *str = name->name;
        struct list_head *p, *head;

        spin_lock(&dcache_lock);
        spin_lock(&sbi->lookup_lock);
        head = &sbi->active_list;
        list_for_each(p, head) {
                struct autofs_info *ino;
                struct dentry *dentry;
                struct qstr *qstr;

                ino = list_entry(p, struct autofs_info, active);
                dentry = ino->dentry;

                spin_lock(&dentry->d_lock);

                /* Already gone? */
                if (atomic_read(&dentry->d_count) == 0)
                        goto next;

                qstr = &dentry->d_name;

                if (dentry->d_name.hash != hash)
                        goto next;
                if (dentry->d_parent != parent)
                        goto next;

                if (qstr->len != len)
                        goto next;
                if (memcmp(qstr->name, str, len))
                        goto next;

                if (d_unhashed(dentry)) {
                        dget(dentry);
                        spin_unlock(&dentry->d_lock);
                        spin_unlock(&sbi->lookup_lock);
                        spin_unlock(&dcache_lock);
                        return dentry;
                }
next:
                spin_unlock(&dentry->d_lock);
        }
        spin_unlock(&sbi->lookup_lock);
        spin_unlock(&dcache_lock);

        return NULL;
}

static struct dentry *autofs4_lookup_expiring(struct autofs_sb_info *sbi, struct dentry *parent, struct qstr *name)
{
        unsigned int len = name->len;
        unsigned int hash = name->hash;
        const unsigned char *str = name->name;
        struct list_head *p, *head;

        spin_lock(&dcache_lock);
        spin_lock(&sbi->lookup_lock);
        head = &sbi->expiring_list;
        list_for_each(p, head) {
                struct autofs_info *ino;
                struct dentry *dentry;
                struct qstr *qstr;

                ino = list_entry(p, struct autofs_info, expiring);
                dentry = ino->dentry;

                spin_lock(&dentry->d_lock);

                /* Bad luck, we've already been dentry_iput */
                if (!dentry->d_inode)
                        goto next;

                qstr = &dentry->d_name;

                if (dentry->d_name.hash != hash)
                        goto next;
                if (dentry->d_parent != parent)
                        goto next;

                if (qstr->len != len)
                        goto next;
                if (memcmp(qstr->name, str, len))
                        goto next;

                if (d_unhashed(dentry)) {
                        dget(dentry);
                        spin_unlock(&dentry->d_lock);
                        spin_unlock(&sbi->lookup_lock);
                        spin_unlock(&dcache_lock);
                        return dentry;
                }
next:
                spin_unlock(&dentry->d_lock);
        }
        spin_unlock(&sbi->lookup_lock);
        spin_unlock(&dcache_lock);

        return NULL;
}

/* Lookups in the root directory */
static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
{
        struct autofs_sb_info *sbi;
        struct autofs_info *ino;
        struct dentry *expiring, *unhashed;
        int oz_mode;

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

        /* File name too long to exist */
        if (dentry->d_name.len > NAME_MAX)
                return ERR_PTR(-ENAMETOOLONG);

        sbi = autofs4_sbi(dir->i_sb);
        oz_mode = autofs4_oz_mode(sbi);

        DPRINTK("pid = %u, pgrp = %u, catatonic = %d, oz_mode = %d",
                 current->pid, task_pgrp_nr(current), sbi->catatonic, oz_mode);

        expiring = autofs4_lookup_expiring(sbi, dentry->d_parent, &dentry->d_name);
        if (expiring) {
                /*
                 * If we are racing with expire the request might not
                 * be quite complete but the directory has been removed
                 * so it must have been successful, so just wait for it.
                 */
                ino = autofs4_dentry_ino(expiring);
                spin_lock(&sbi->fs_lock);
                if (ino->flags & AUTOFS_INF_EXPIRING) {
                        spin_unlock(&sbi->fs_lock);
                        DPRINTK("wait for incomplete expire %p name=%.*s",
                                expiring, expiring->d_name.len,
                                expiring->d_name.name);
                        autofs4_wait(sbi, expiring, NFY_NONE);
                        wait_for_completion(&ino->expire_complete);
                        DPRINTK("request completed");
                        goto cont;
                }
                spin_unlock(&sbi->fs_lock);
cont:
                spin_lock(&sbi->lookup_lock);
                if (!list_empty(&ino->expiring))
                        list_del_init(&ino->expiring);
                spin_unlock(&sbi->lookup_lock);
                dput(expiring);
        }

        unhashed = autofs4_lookup_active(sbi, dentry->d_parent, &dentry->d_name);
        if (unhashed)
                dentry = unhashed;
        else {
                /*
                 * Mark the dentry incomplete but don't hash it. We do this
                 * to serialize our inode creation operations (symlink and
                 * mkdir) which prevents deadlock during the callback to
                 * the daemon. Subsequent user space lookups for the same
                 * dentry are placed on the wait queue while the daemon
                 * itself is allowed passage unresticted so the create
                 * operation itself can then hash the dentry. Finally,
                 * we check for the hashed dentry and return the newly
                 * hashed dentry.
                 */
                dentry->d_op = &autofs4_root_dentry_operations;

                /*
                 * And we need to ensure that the same dentry is used for
                 * all following lookup calls until it is hashed so that
                 * the dentry flags are persistent throughout the request.
                 */
                ino = autofs4_init_ino(NULL, sbi, 0555);
                if (!ino)
                        return ERR_PTR(-ENOMEM);

                dentry->d_fsdata = ino;
                ino->dentry = dentry;

                spin_lock(&sbi->lookup_lock);
                list_add(&ino->active, &sbi->active_list);
                spin_unlock(&sbi->lookup_lock);

                d_instantiate(dentry, NULL);
        }

        if (!oz_mode) {
                spin_lock(&dentry->d_lock);
                dentry->d_flags |= DCACHE_AUTOFS_PENDING;
                spin_unlock(&dentry->d_lock);
                if (dentry->d_op && dentry->d_op->d_revalidate) {
                        mutex_unlock(&dir->i_mutex);
                        (dentry->d_op->d_revalidate)(dentry, nd);
                        mutex_lock(&dir->i_mutex);
                }
        }

        /*
         * If we are still pending, check if we had to handle
         * a signal. If so we can force a restart..
         */
        if (dentry->d_flags & DCACHE_AUTOFS_PENDING) {
                /* See if we were interrupted */
                if (signal_pending(current)) {
                        sigset_t *sigset = &current->pending.signal;
                        if (sigismember (sigset, SIGKILL) ||
                            sigismember (sigset, SIGQUIT) ||
                            sigismember (sigset, SIGINT)) {
                            if (unhashed)
                                dput(unhashed);
                            return ERR_PTR(-ERESTARTNOINTR);
                        }
                }
                if (!oz_mode) {
                        spin_lock(&dentry->d_lock);
                        dentry->d_flags &= ~DCACHE_AUTOFS_PENDING;
                        spin_unlock(&dentry->d_lock);
                }
        }

        /*
         * If this dentry is unhashed, then we shouldn't honour this
         * lookup.  Returning ENOENT here doesn't do the right thing
         * for all system calls, but it should be OK for the operations
         * we permit from an autofs.
         */
        if (!oz_mode && d_unhashed(dentry)) {
                /*
                 * A user space application can (and has done in the past)
                 * remove and re-create this directory during the callback.
                 * This can leave us with an unhashed dentry, but a
                 * successful mount!  So we need to perform another
                 * cached lookup in case the dentry now exists.
                 */
                struct dentry *parent = dentry->d_parent;
                struct dentry *new = d_lookup(parent, &dentry->d_name);
                if (new != NULL)
                        dentry = new;
                else
                        dentry = ERR_PTR(-ENOENT);

                if (unhashed)
                        dput(unhashed);

                return dentry;
        }

        if (unhashed)
                return unhashed;

        return NULL;
}

static int autofs4_dir_symlink(struct inode *dir, 
                               struct dentry *dentry,
                               const char *symname)
{
        struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
        struct autofs_info *ino = autofs4_dentry_ino(dentry);
        struct autofs_info *p_ino;
        struct inode *inode;
        char *cp;

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

        if (!autofs4_oz_mode(sbi))
                return -EACCES;

        ino = autofs4_init_ino(ino, sbi, S_IFLNK | 0555);
        if (!ino)
                return -ENOMEM;

        spin_lock(&sbi->lookup_lock);
        if (!list_empty(&ino->active))
                list_del_init(&ino->active);
        spin_unlock(&sbi->lookup_lock);

        ino->size = strlen(symname);
        cp = kmalloc(ino->size + 1, GFP_KERNEL);
        if (!cp) {
                if (!dentry->d_fsdata)
                        kfree(ino);
                return -ENOMEM;
        }

        strcpy(cp, symname);

        inode = autofs4_get_inode(dir->i_sb, ino);
        if (!inode) {
                kfree(cp);
                if (!dentry->d_fsdata)
                        kfree(ino);
                return -ENOMEM;
        }
        d_add(dentry, inode);

        if (dir == dir->i_sb->s_root->d_inode)
                dentry->d_op = &autofs4_root_dentry_operations;
        else
                dentry->d_op = &autofs4_dentry_operations;

        dentry->d_fsdata = ino;
        ino->dentry = dget(dentry);
        atomic_inc(&ino->count);
        p_ino = autofs4_dentry_ino(dentry->d_parent);
        if (p_ino && dentry->d_parent != dentry)
                atomic_inc(&p_ino->count);
        ino->inode = inode;

        ino->u.symlink = cp;
        dir->i_mtime = CURRENT_TIME;

        return 0;
}

/*
 * NOTE!
 *
 * Normal filesystems would do a "d_delete()" to tell the VFS dcache
 * that the file no longer exists. However, doing that means that the
 * VFS layer can turn the dentry into a negative dentry.  We don't want
 * this, because the unlink is probably the result of an expire.
 * We simply d_drop it and add it to a expiring list in the super block,
 * which allows the dentry lookup to check for an incomplete expire.
 *
 * If a process is blocked on the dentry waiting for the expire to finish,
 * it will invalidate the dentry and try to mount with a new one.
 *
 * Also see autofs4_dir_rmdir()..
 */
static int autofs4_dir_unlink(struct inode *dir, struct dentry *dentry)
{
        struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
        struct autofs_info *ino = autofs4_dentry_ino(dentry);
        struct autofs_info *p_ino;
        
        /* This allows root to remove symlinks */
        if (!autofs4_oz_mode(sbi) && !capable(CAP_SYS_ADMIN))
                return -EACCES;

        if (atomic_dec_and_test(&ino->count)) {
                p_ino = autofs4_dentry_ino(dentry->d_parent);
                if (p_ino && dentry->d_parent != dentry)
                        atomic_dec(&p_ino->count);
        }
        dput(ino->dentry);

        dentry->d_inode->i_size = 0;
        clear_nlink(dentry->d_inode);

        dir->i_mtime = CURRENT_TIME;

        spin_lock(&dcache_lock);
        spin_lock(&sbi->lookup_lock);
        if (list_empty(&ino->expiring))
                list_add(&ino->expiring, &sbi->expiring_list);
        spin_unlock(&sbi->lookup_lock);
        spin_lock(&dentry->d_lock);
        __d_drop(dentry);
        spin_unlock(&dentry->d_lock);
        spin_unlock(&dcache_lock);

        return 0;
}

static int autofs4_dir_rmdir(struct inode *dir, struct dentry *dentry)
{
        struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
        struct autofs_info *ino = autofs4_dentry_ino(dentry);
        struct autofs_info *p_ino;
        
        DPRINTK("dentry %p, removing %.*s",
                dentry, dentry->d_name.len, dentry->d_name.name);

        if (!autofs4_oz_mode(sbi))
                return -EACCES;

        spin_lock(&dcache_lock);
        if (!list_empty(&dentry->d_subdirs)) {
                spin_unlock(&dcache_lock);
                return -ENOTEMPTY;
        }
        spin_lock(&sbi->lookup_lock);
        if (list_empty(&ino->expiring))
                list_add(&ino->expiring, &sbi->expiring_list);
        spin_unlock(&sbi->lookup_lock);
        spin_lock(&dentry->d_lock);
        __d_drop(dentry);
        spin_unlock(&dentry->d_lock);
        spin_unlock(&dcache_lock);

        if (atomic_dec_and_test(&ino->count)) {
                p_ino = autofs4_dentry_ino(dentry->d_parent);
                if (p_ino && dentry->d_parent != dentry)
                        atomic_dec(&p_ino->count);
        }
        dput(ino->dentry);
        dentry->d_inode->i_size = 0;
        clear_nlink(dentry->d_inode);

        if (dir->i_nlink)
                drop_nlink(dir);

        return 0;
}

static int autofs4_dir_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
        struct autofs_sb_info *sbi = autofs4_sbi(dir->i_sb);
        struct autofs_info *ino = autofs4_dentry_ino(dentry);
        struct autofs_info *p_ino;
        struct inode *inode;

        if (!autofs4_oz_mode(sbi))
                return -EACCES;

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

        ino = autofs4_init_ino(ino, sbi, S_IFDIR | 0555);
        if (!ino)
                return -ENOMEM;

        spin_lock(&sbi->lookup_lock);
        if (!list_empty(&ino->active))
                list_del_init(&ino->active);
        spin_unlock(&sbi->lookup_lock);

        inode = autofs4_get_inode(dir->i_sb, ino);
        if (!inode) {
                if (!dentry->d_fsdata)
                        kfree(ino);
                return -ENOMEM;
        }
        d_add(dentry, inode);

        if (dir == dir->i_sb->s_root->d_inode)
                dentry->d_op = &autofs4_root_dentry_operations;
        else
                dentry->d_op = &autofs4_dentry_operations;

        dentry->d_fsdata = ino;
        ino->dentry = dget(dentry);
        atomic_inc(&ino->count);
        p_ino = autofs4_dentry_ino(dentry->d_parent);
        if (p_ino && dentry->d_parent != dentry)
                atomic_inc(&p_ino->count);
        ino->inode = inode;
        inc_nlink(dir);
        dir->i_mtime = CURRENT_TIME;

        return 0;
}

/* Get/set timeout ioctl() operation */
static inline int autofs4_get_set_timeout(struct autofs_sb_info *sbi,
                                         unsigned long __user *p)
{
        int rv;
        unsigned long ntimeout;

        if ((rv = get_user(ntimeout, p)) ||
             (rv = put_user(sbi->exp_timeout/HZ, p)))
                return rv;

        if (ntimeout > ULONG_MAX/HZ)
                sbi->exp_timeout = 0;
        else
                sbi->exp_timeout = ntimeout * HZ;

        return 0;
}

/* Return protocol version */
static inline int autofs4_get_protover(struct autofs_sb_info *sbi, int __user *p)
{
        return put_user(sbi->version, p);
}

/* Return protocol sub version */
static inline int autofs4_get_protosubver(struct autofs_sb_info *sbi, int __user *p)
{
        return put_user(sbi->sub_version, p);
}

/*
 * Tells the daemon whether we need to reghost or not. Also, clears
 * the reghost_needed flag.
 */
static inline int autofs4_ask_reghost(struct autofs_sb_info *sbi, int __user *p)
{
        int status;

        DPRINTK("returning %d", sbi->needs_reghost);

        status = put_user(sbi->needs_reghost, p);
        if (status)
                return status;

        sbi->needs_reghost = 0;
        return 0;
}

/*
 * Enable / Disable reghosting ioctl() operation
 */
static inline int autofs4_toggle_reghost(struct autofs_sb_info *sbi, int __user *p)
{
        int status;
        int val;

        status = get_user(val, p);

        DPRINTK("reghost = %d", val);

        if (status)
                return status;

        /* turn on/off reghosting, with the val */
        sbi->reghost_enabled = val;
        return 0;
}

/*
* Tells the daemon whether it can umount the autofs mount.
*/
static inline int autofs4_ask_umount(struct vfsmount *mnt, int __user *p)
{
        int status = 0;

        if (may_umount(mnt))
                status = 1;

        DPRINTK("returning %d", status);

        status = put_user(status, p);

        return status;
}

/* Identify autofs4_dentries - this is so we can tell if there's
   an extra dentry refcount or not.  We only hold a refcount on the
   dentry if its non-negative (ie, d_inode != NULL)
*/
int is_autofs4_dentry(struct dentry *dentry)
{
        return dentry && dentry->d_inode &&
                (dentry->d_op == &autofs4_root_dentry_operations ||
                 dentry->d_op == &autofs4_dentry_operations) &&
                dentry->d_fsdata != NULL;
}

/*
 * ioctl()'s on the root directory is the chief method for the daemon to
 * generate kernel reactions
 */
static int autofs4_root_ioctl(struct inode *inode, struct file *filp,
                             unsigned int cmd, unsigned long arg)
{
        struct autofs_sb_info *sbi = autofs4_sbi(inode->i_sb);
        void __user *p = (void __user *)arg;

        DPRINTK("cmd = 0x%08x, arg = 0x%08lx, sbi = %p, pgrp = %u",
                cmd,arg,sbi,task_pgrp_nr(current));

        if (_IOC_TYPE(cmd) != _IOC_TYPE(AUTOFS_IOC_FIRST) ||
             _IOC_NR(cmd) - _IOC_NR(AUTOFS_IOC_FIRST) >= AUTOFS_IOC_COUNT)
                return -ENOTTY;
        
        if (!autofs4_oz_mode(sbi) && !capable(CAP_SYS_ADMIN))
                return -EPERM;
        
        switch(cmd) {
        case AUTOFS_IOC_READY:  /* Wait queue: go ahead and retry */
                return autofs4_wait_release(sbi,(autofs_wqt_t)arg,0);
        case AUTOFS_IOC_FAIL:   /* Wait queue: fail with ENOENT */
                return autofs4_wait_release(sbi,(autofs_wqt_t)arg,-ENOENT);
        case AUTOFS_IOC_CATATONIC: /* Enter catatonic mode (daemon shutdown) */
                autofs4_catatonic_mode(sbi);
                return 0;
        case AUTOFS_IOC_PROTOVER: /* Get protocol version */
                return autofs4_get_protover(sbi, p);
        case AUTOFS_IOC_PROTOSUBVER: /* Get protocol sub version */
                return autofs4_get_protosubver(sbi, p);
        case AUTOFS_IOC_SETTIMEOUT:
                return autofs4_get_set_timeout(sbi, p);

        case AUTOFS_IOC_TOGGLEREGHOST:
                return autofs4_toggle_reghost(sbi, p);
        case AUTOFS_IOC_ASKREGHOST:
                return autofs4_ask_reghost(sbi, p);

        case AUTOFS_IOC_ASKUMOUNT:
                return autofs4_ask_umount(filp->f_path.mnt, p);

        /* return a single thing to expire */
        case AUTOFS_IOC_EXPIRE:
                return autofs4_expire_run(inode->i_sb,filp->f_path.mnt,sbi, p);
        /* same as above, but can send multiple expires through pipe */
        case AUTOFS_IOC_EXPIRE_MULTI:
                return autofs4_expire_multi(inode->i_sb,filp->f_path.mnt,sbi, p);

        default:
                return -ENOSYS;
        }
}