/*
   * 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/module.h>
  #include <linux/dcache.h>
  #include <linux/gfp.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 <linux/sunrpc/gss_api.h>
  #include "internal.h"
  
  #define NFSDBG_FACILITY		NFSDBG_VFS
  
  static void nfs_expire_automounts(struct work_struct *work);
  
  static LIST_HEAD(nfs_automount_list);
  static DECLARE_DELAYED_WORK(nfs_automount_task, nfs_expire_automounts);
  int nfs_mountpoint_expiry_timeout = 500 * HZ;
  
  /*
   * nfs_path - reconstruct the path given an arbitrary dentry
   * @base - used to return pointer to the end of devname part of path
   * @dentry - pointer to dentry
   * @buffer - result buffer
   * @buflen - length of buffer
   * @flags - options (see below)
   *
   * Helper function for constructing the server pathname
   * by 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
   * and in generating /proc/mounts and friends.
   *
   * Supported flags:
   * NFS_PATH_CANONICAL: ensure there is exactly one slash after
   *		       the original device (export) name
   *		       (if unset, the original name is returned verbatim)
   */
  char *nfs_path(char **p, struct dentry *dentry, char *buffer, ssize_t buflen,
  	       unsigned flags)
  {
  	char *end;
  	int namelen;
  	unsigned seq;
  	const char *base;
  
  rename_retry:
  	end = buffer+buflen;
  	*--end = '\0';
  	buflen--;
  
  	seq = read_seqbegin(&rename_lock);
  	rcu_read_lock();
  	while (1) {
  		spin_lock(&dentry->d_lock);
  		if (IS_ROOT(dentry))
  			break;
  		namelen = dentry->d_name.len;
  		buflen -= namelen + 1;
  		if (buflen < 0)
  			goto Elong_unlock;
  		end -= namelen;
  		memcpy(end, dentry->d_name.name, namelen);
  		*--end = '/';
  		spin_unlock(&dentry->d_lock);
  		dentry = dentry->d_parent;
  	}
  	if (read_seqretry(&rename_lock, seq)) {
  		spin_unlock(&dentry->d_lock);
  		rcu_read_unlock();
  		goto rename_retry;
  	}
  	if ((flags & NFS_PATH_CANONICAL) && *end != '/') {
  		if (--buflen < 0) {
  			spin_unlock(&dentry->d_lock);
  			rcu_read_unlock();
  			goto Elong;
  		}
  		*--end = '/';
  	}
  	*p = end;
  	base = dentry->d_fsdata;
  	if (!base) {
  		spin_unlock(&dentry->d_lock);
  		rcu_read_unlock();
  		WARN_ON(1);
  		return end;
  	}
  	namelen = strlen(base);
  	if (flags & NFS_PATH_CANONICAL) {
  		/* Strip off excess slashes in base string */
  		while (namelen > 0 && base[namelen - 1] == '/')
  			namelen--;
  	}
  	buflen -= namelen;
  	if (buflen < 0) {
  		spin_unlock(&dentry->d_lock);
  		rcu_read_unlock();
  		goto Elong;
  	}
  	end -= namelen;
  	memcpy(end, base, namelen);
  	spin_unlock(&dentry->d_lock);
  	rcu_read_unlock();
  	return end;
  Elong_unlock:
  	spin_unlock(&dentry->d_lock);
  	rcu_read_unlock();
  	if (read_seqretry(&rename_lock, seq))
  		goto rename_retry;
  Elong:
  	return ERR_PTR(-ENAMETOOLONG);
  }
  EXPORT_SYMBOL_GPL(nfs_path);
  
  /*
   * nfs_d_automount - Handle crossing a mountpoint on the server
   * @path - The mountpoint
   *
   * 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.
   */
  struct vfsmount *nfs_d_automount(struct path *path)
  {
  	struct vfsmount *mnt;
  	struct nfs_server *server = NFS_SERVER(d_inode(path->dentry));
  	struct nfs_fh *fh = NULL;
  	struct nfs_fattr *fattr = NULL;
  
  	dprintk("--> nfs_d_automount()
  ");
  
  	mnt = ERR_PTR(-ESTALE);
  	if (IS_ROOT(path->dentry))
  		goto out_nofree;
  
  	mnt = ERR_PTR(-ENOMEM);
  	fh = nfs_alloc_fhandle();
  	fattr = nfs_alloc_fattr();
  	if (fh == NULL || fattr == NULL)
  		goto out;
  
  	dprintk("%s: enter
  ", __func__);
  
  	mnt = server->nfs_client->rpc_ops->submount(server, path->dentry, fh, fattr);
  	if (IS_ERR(mnt))
  		goto out;
  
  	dprintk("%s: done, success
  ", __func__);
  	mntget(mnt); /* prevent immediate expiration */
  	mnt_set_expiry(mnt, &nfs_automount_list);
  	schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout);
  
  out:
  	nfs_free_fattr(fattr);
  	nfs_free_fhandle(fh);
  out_nofree:
  	if (IS_ERR(mnt))
  		dprintk("<-- %s(): error %ld
  ", __func__, PTR_ERR(mnt));
  	else
  		dprintk("<-- %s() = %p
  ", __func__, mnt);
  	return mnt;
  }
  
  static int
  nfs_namespace_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
  {
  	if (NFS_FH(d_inode(dentry))->size != 0)
  		return nfs_getattr(mnt, dentry, stat);
  	generic_fillattr(d_inode(dentry), stat);
  	return 0;
  }
  
  static int
  nfs_namespace_setattr(struct dentry *dentry, struct iattr *attr)
  {
  	if (NFS_FH(d_inode(dentry))->size != 0)
  		return nfs_setattr(dentry, attr);
  	return -EACCES;
  }
  
  const struct inode_operations nfs_mountpoint_inode_operations = {
  	.getattr	= nfs_getattr,
  	.setattr	= nfs_setattr,
  };
  
  const struct inode_operations nfs_referral_inode_operations = {
  	.getattr	= nfs_namespace_getattr,
  	.setattr	= nfs_namespace_setattr,
  };
  
  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)
  {
  	return vfs_kern_mount(&nfs_xdev_fs_type, 0, devname, mountdata);
  }
  
  /**
   * nfs_do_submount - set up mountpoint when crossing a filesystem boundary
   * @dentry - parent directory
   * @fh - filehandle for new root dentry
   * @fattr - attributes for new root inode
   * @authflavor - security flavor to use when performing the mount
   *
   */
  struct vfsmount *nfs_do_submount(struct dentry *dentry, struct nfs_fh *fh,
  				 struct nfs_fattr *fattr, rpc_authflavor_t authflavor)
  {
  	struct nfs_clone_mount mountdata = {
  		.sb = dentry->d_sb,
  		.dentry = dentry,
  		.fh = fh,
  		.fattr = fattr,
  		.authflavor = authflavor,
  	};
  	struct vfsmount *mnt = ERR_PTR(-ENOMEM);
  	char *page = (char *) __get_free_page(GFP_USER);
  	char *devname;
  
  	dprintk("--> nfs_do_submount()
  ");
  
  	dprintk("%s: submounting on %pd2
  ", __func__,
  			dentry);
  	if (page == NULL)
  		goto out;
  	devname = nfs_devname(dentry, page, PAGE_SIZE);
  	mnt = (struct vfsmount *)devname;
  	if (IS_ERR(devname))
  		goto free_page;
  	mnt = nfs_do_clone_mount(NFS_SB(dentry->d_sb), devname, &mountdata);
  free_page:
  	free_page((unsigned long)page);
  out:
  	dprintk("%s: done
  ", __func__);
  
  	dprintk("<-- nfs_do_submount() = %p
  ", mnt);
  	return mnt;
  }
  EXPORT_SYMBOL_GPL(nfs_do_submount);
  
  struct vfsmount *nfs_submount(struct nfs_server *server, struct dentry *dentry,
  			      struct nfs_fh *fh, struct nfs_fattr *fattr)
  {
  	int err;
  	struct dentry *parent = dget_parent(dentry);
  
  	/* Look it up again to get its attributes */
  	err = server->nfs_client->rpc_ops->lookup(d_inode(parent), &dentry->d_name, fh, fattr, NULL);
  	dput(parent);
  	if (err != 0)
  		return ERR_PTR(err);
  
  	return nfs_do_submount(dentry, fh, fattr, server->client->cl_auth->au_flavor);
  }
  EXPORT_SYMBOL_GPL(nfs_submount);