/*
 * linux/fs/nfs/namespace.c
 *
 * Copyright (C) 2005 Trond Myklebust <Trond.Myklebust@netapp.com>
 * - Modified by David Howells <dhowells@redhat.com>
 *
 * NFS namespace
 */

#include <linux/dcache.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/nfs_fs.h>
#include <linux/string.h>
#include <linux/sunrpc/clnt.h>
#include <linux/vfs.h>
#include "internal.h"

#define NFSDBG_FACILITY         NFSDBG_VFS

static void nfs_expire_automounts(struct work_struct *work);

LIST_HEAD(nfs_automount_list);
static DECLARE_DELAYED_WORK(nfs_automount_task, nfs_expire_automounts);
int nfs_mountpoint_expiry_timeout = 500 * HZ;

static struct vfsmount *nfs_do_submount(const struct vfsmount *mnt_parent,
                                        const struct dentry *dentry,
                                        struct nfs_fh *fh,
                                        struct nfs_fattr *fattr);

/*
 * nfs_path - reconstruct the path given an arbitrary dentry
 * @base - arbitrary string to prepend to the path
 * @droot - pointer to root dentry for mountpoint
 * @dentry - pointer to dentry
 * @buffer - result buffer
 * @buflen - length of buffer
 *
 * Helper function for constructing the path from the
 * root dentry to an arbitrary hashed dentry.
 *
 * This is mainly for use in figuring out the path on the
 * server side when automounting on top of an existing partition.
 */
char *nfs_path(const char *base,
               const struct dentry *droot,
               const struct dentry *dentry,
               char *buffer, ssize_t buflen)
{
        char *end = buffer+buflen;
        int namelen;

        *--end = '\0';
        buflen--;
        spin_lock(&dcache_lock);
        while (!IS_ROOT(dentry) && dentry != droot) {
                namelen = dentry->d_name.len;
                buflen -= namelen + 1;
                if (buflen < 0)
                        goto Elong_unlock;
                end -= namelen;
                memcpy(end, dentry->d_name.name, namelen);
                *--end = '/';
                dentry = dentry->d_parent;
        }
        spin_unlock(&dcache_lock);
        namelen = strlen(base);
        /* Strip off excess slashes in base string */
        while (namelen > 0 && base[namelen - 1] == '/')
                namelen--;
        buflen -= namelen;
        if (buflen < 0)
                goto Elong;
        end -= namelen;
        memcpy(end, base, namelen);
        return end;
Elong_unlock:
        spin_unlock(&dcache_lock);
Elong:
        return ERR_PTR(-ENAMETOOLONG);
}

/*
 * nfs_follow_mountpoint - handle crossing a mountpoint on the server
 * @dentry - dentry of mountpoint
 * @nd - nameidata info
 *
 * When we encounter a mountpoint on the server, we want to set up
 * a mountpoint on the client too, to prevent inode numbers from
 * colliding, and to allow "df" to work properly.
 * On NFSv4, we also want to allow for the fact that different
 * filesystems may be migrated to different servers in a failover
 * situation, and that different filesystems may want to use
 * different security flavours.
 */
static void * nfs_follow_mountpoint(struct dentry *dentry, struct nameidata *nd)
{
        struct vfsmount *mnt;
        struct nfs_server *server = NFS_SERVER(dentry->d_inode);
        struct dentry *parent;
        struct nfs_fh fh;
        struct nfs_fattr fattr;
        int err;

        dprintk("--> nfs_follow_mountpoint()\n");

        BUG_ON(IS_ROOT(dentry));
        dprintk("%s: enter\n", __FUNCTION__);
        dput(nd->dentry);
        nd->dentry = dget(dentry);

        /* Look it up again */
        parent = dget_parent(nd->dentry);
        err = server->nfs_client->rpc_ops->lookup(parent->d_inode,
                                                  &nd->dentry->d_name,
                                                  &fh, &fattr);
        dput(parent);
        if (err != 0)
                goto out_err;

        if (fattr.valid & NFS_ATTR_FATTR_V4_REFERRAL)
                mnt = nfs_do_refmount(nd->mnt, nd->dentry);
        else
                mnt = nfs_do_submount(nd->mnt, nd->dentry, &fh, &fattr);
        err = PTR_ERR(mnt);
        if (IS_ERR(mnt))
                goto out_err;

        mntget(mnt);
        err = do_add_mount(mnt, nd, nd->mnt->mnt_flags|MNT_SHRINKABLE, &nfs_automount_list);
        if (err < 0) {
                mntput(mnt);
                if (err == -EBUSY)
                        goto out_follow;
                goto out_err;
        }
        mntput(nd->mnt);
        dput(nd->dentry);
        nd->mnt = mnt;
        nd->dentry = dget(mnt->mnt_root);
        schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
out:
        dprintk("%s: done, returned %d\n", __FUNCTION__, err);

        dprintk("<-- nfs_follow_mountpoint() = %d\n", err);
        return ERR_PTR(err);
out_err:
        path_release(nd);
        goto out;
out_follow:
        while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
                ;
        err = 0;
        goto out;
}

const struct inode_operations nfs_mountpoint_inode_operations = {
        .follow_link    = nfs_follow_mountpoint,
        .getattr        = nfs_getattr,
};

const struct inode_operations nfs_referral_inode_operations = {
        .follow_link    = nfs_follow_mountpoint,
};

static void nfs_expire_automounts(struct work_struct *work)
{
        struct list_head *list = &nfs_automount_list;

        mark_mounts_for_expiry(list);
        if (!list_empty(list))
                schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
}

void nfs_release_automount_timer(void)
{
        if (list_empty(&nfs_automount_list))
                cancel_delayed_work(&nfs_automount_task);
}

/*
 * Clone a mountpoint of the appropriate type
 */
static struct vfsmount *nfs_do_clone_mount(struct nfs_server *server,
                                           const char *devname,
                                           struct nfs_clone_mount *mountdata)
{
#ifdef CONFIG_NFS_V4
        struct vfsmount *mnt = NULL;
        switch (server->nfs_client->cl_nfsversion) {
                case 2:
                case 3:
                        mnt = vfs_kern_mount(&nfs_xdev_fs_type, 0, devname, mountdata);
                        break;
                case 4:
                        mnt = vfs_kern_mount(&nfs4_xdev_fs_type, 0, devname, mountdata);
        }
        return mnt;
#else
        return vfs_kern_mount(&nfs_xdev_fs_type, 0, devname, mountdata);
#endif
}

/**
 * nfs_do_submount - set up mountpoint when crossing a filesystem boundary
 * @mnt_parent - mountpoint of parent directory
 * @dentry - parent directory
 * @fh - filehandle for new root dentry
 * @fattr - attributes for new root inode
 *
 */
static struct vfsmount *nfs_do_submount(const struct vfsmount *mnt_parent,
                                        const struct dentry *dentry,
                                        struct nfs_fh *fh,
                                        struct nfs_fattr *fattr)
{
        struct nfs_clone_mount mountdata = {
                .sb = mnt_parent->mnt_sb,
                .dentry = dentry,
                .fh = fh,
                .fattr = fattr,
        };
        struct vfsmount *mnt = ERR_PTR(-ENOMEM);
        char *page = (char *) __get_free_page(GFP_USER);
        char *devname;

        dprintk("--> nfs_do_submount()\n");

        dprintk("%s: submounting on %s/%s\n", __FUNCTION__,
                        dentry->d_parent->d_name.name,
                        dentry->d_name.name);
        if (page == NULL)
                goto out;
        devname = nfs_devname(mnt_parent, dentry, page, PAGE_SIZE);
        mnt = (struct vfsmount *)devname;
        if (IS_ERR(devname))
                goto free_page;
        mnt = nfs_do_clone_mount(NFS_SB(mnt_parent->mnt_sb), devname, &mountdata);
free_page:
        free_page((unsigned long)page);
out:
        dprintk("%s: done\n", __FUNCTION__);

        dprintk("<-- nfs_do_submount() = %p\n", mnt);
        return mnt;
}