/* mountpoint management
 *
 * Copyright (C) 2002 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include "internal.h"


static struct dentry *afs_mntpt_lookup(struct inode *dir,
                                       struct dentry *dentry,
                                       struct nameidata *nd);
static int afs_mntpt_open(struct inode *inode, struct file *file);
static void *afs_mntpt_follow_link(struct dentry *dentry, struct nameidata *nd);
static void afs_mntpt_expiry_timed_out(struct work_struct *work);

const struct file_operations afs_mntpt_file_operations = {
        .open           = afs_mntpt_open,
};

const struct inode_operations afs_mntpt_inode_operations = {
        .lookup         = afs_mntpt_lookup,
        .follow_link    = afs_mntpt_follow_link,
        .readlink       = page_readlink,
        .getattr        = afs_getattr,
};

static LIST_HEAD(afs_vfsmounts);
static DECLARE_DELAYED_WORK(afs_mntpt_expiry_timer, afs_mntpt_expiry_timed_out);

static unsigned long afs_mntpt_expiry_timeout = 10 * 60;

/*
 * check a symbolic link to see whether it actually encodes a mountpoint
 * - sets the AFS_VNODE_MOUNTPOINT flag on the vnode appropriately
 */
int afs_mntpt_check_symlink(struct afs_vnode *vnode, struct key *key)
{
        struct file file = {
                .private_data = key,
        };
        struct page *page;
        size_t size;
        char *buf;
        int ret;

        _enter("{%x:%u,%u}",
               vnode->fid.vid, vnode->fid.vnode, vnode->fid.unique);

        /* read the contents of the symlink into the pagecache */
        page = read_mapping_page(AFS_VNODE_TO_I(vnode)->i_mapping, 0, &file);
        if (IS_ERR(page)) {
                ret = PTR_ERR(page);
                goto out;
        }

        ret = -EIO;
        if (PageError(page))
                goto out_free;

        buf = kmap(page);

        /* examine the symlink's contents */
        size = vnode->status.size;
        _debug("symlink to %*.*s", (int) size, (int) size, buf);

        if (size > 2 &&
            (buf[0] == '%' || buf[0] == '#') &&
            buf[size - 1] == '.'
            ) {
                _debug("symlink is a mountpoint");
                spin_lock(&vnode->lock);
                set_bit(AFS_VNODE_MOUNTPOINT, &vnode->flags);
                spin_unlock(&vnode->lock);
        }

        ret = 0;

        kunmap(page);
out_free:
        page_cache_release(page);
out:
        _leave(" = %d", ret);
        return ret;
}

/*
 * no valid lookup procedure on this sort of dir
 */
static struct dentry *afs_mntpt_lookup(struct inode *dir,
                                       struct dentry *dentry,
                                       struct nameidata *nd)
{
        _enter("%p,%p{%p{%s},%s}",
               dir,
               dentry,
               dentry->d_parent,
               dentry->d_parent ?
               dentry->d_parent->d_name.name : (const unsigned char *) "",
               dentry->d_name.name);

        return ERR_PTR(-EREMOTE);
}

/*
 * no valid open procedure on this sort of dir
 */
static int afs_mntpt_open(struct inode *inode, struct file *file)
{
        _enter("%p,%p{%p{%s},%s}",
               inode, file,
               file->f_path.dentry->d_parent,
               file->f_path.dentry->d_parent ?
               file->f_path.dentry->d_parent->d_name.name :
               (const unsigned char *) "",
               file->f_path.dentry->d_name.name);

        return -EREMOTE;
}

/*
 * create a vfsmount to be automounted
 */
static struct vfsmount *afs_mntpt_do_automount(struct dentry *mntpt)
{
        struct afs_super_info *super;
        struct vfsmount *mnt;
        struct page *page = NULL;
        size_t size;
        char *buf, *devname = NULL, *options = NULL;
        int ret;

        _enter("{%s}", mntpt->d_name.name);

        BUG_ON(!mntpt->d_inode);

        ret = -EINVAL;
        size = mntpt->d_inode->i_size;
        if (size > PAGE_SIZE - 1)
                goto error;

        ret = -ENOMEM;
        devname = (char *) get_zeroed_page(GFP_KERNEL);
        if (!devname)
                goto error;

        options = (char *) get_zeroed_page(GFP_KERNEL);
        if (!options)
                goto error;

        /* read the contents of the AFS special symlink */
        page = read_mapping_page(mntpt->d_inode->i_mapping, 0, NULL);
        if (IS_ERR(page)) {
                ret = PTR_ERR(page);
                goto error;
        }

        ret = -EIO;
        if (PageError(page))
                goto error;

        buf = kmap_atomic(page, KM_USER0);
        memcpy(devname, buf, size);
        kunmap_atomic(buf, KM_USER0);
        page_cache_release(page);
        page = NULL;

        /* work out what options we want */
        super = AFS_FS_S(mntpt->d_sb);
        memcpy(options, "cell=", 5);
        strcpy(options + 5, super->volume->cell->name);
        if (super->volume->type == AFSVL_RWVOL)
                strcat(options, ",rwpath");

        /* try and do the mount */
        _debug("--- attempting mount %s -o %s ---", devname, options);
        mnt = vfs_kern_mount(&afs_fs_type, 0, devname, options);
        _debug("--- mount result %p ---", mnt);

        free_page((unsigned long) devname);
        free_page((unsigned long) options);
        _leave(" = %p", mnt);
        return mnt;

error:
        if (page)
                page_cache_release(page);
        if (devname)
                free_page((unsigned long) devname);
        if (options)
                free_page((unsigned long) options);
        _leave(" = %d", ret);
        return ERR_PTR(ret);
}

/*
 * follow a link from a mountpoint directory, thus causing it to be mounted
 */
static void *afs_mntpt_follow_link(struct dentry *dentry, struct nameidata *nd)
{
        struct vfsmount *newmnt;
        int err;

        _enter("%p{%s},{%s:%p{%s},}",
               dentry,
               dentry->d_name.name,
               nd->path.mnt->mnt_devname,
               dentry,
               nd->path.dentry->d_name.name);

        dput(nd->path.dentry);
        nd->path.dentry = dget(dentry);

        newmnt = afs_mntpt_do_automount(nd->path.dentry);
        if (IS_ERR(newmnt)) {
                path_put(&nd->path);
                return (void *)newmnt;
        }

        mntget(newmnt);
        err = do_add_mount(newmnt, &nd->path, MNT_SHRINKABLE, &afs_vfsmounts);
        switch (err) {
        case 0:
                path_put(&nd->path);
                nd->path.mnt = newmnt;
                nd->path.dentry = dget(newmnt->mnt_root);
                schedule_delayed_work(&afs_mntpt_expiry_timer,
                                      afs_mntpt_expiry_timeout * HZ);
                break;
        case -EBUSY:
                /* someone else made a mount here whilst we were busy */
                while (d_mountpoint(nd->path.dentry) &&
                       follow_down(&nd->path))
                        ;
                err = 0;
        default:
                mntput(newmnt);
                break;
        }

        _leave(" = %d", err);
        return ERR_PTR(err);
}

/*
 * handle mountpoint expiry timer going off
 */
static void afs_mntpt_expiry_timed_out(struct work_struct *work)
{
        _enter("");

        if (!list_empty(&afs_vfsmounts)) {
                mark_mounts_for_expiry(&afs_vfsmounts);
                schedule_delayed_work(&afs_mntpt_expiry_timer,
                                      afs_mntpt_expiry_timeout * HZ);
        }

        _leave("");
}

/*
 * kill the AFS mountpoint timer if it's still running
 */
void afs_mntpt_kill_timer(void)
{
        _enter("");

        ASSERT(list_empty(&afs_vfsmounts));
        cancel_delayed_work(&afs_mntpt_expiry_timer);
        flush_scheduled_work();
}