// SPDX-License-Identifier: GPL-2.0-only

  /*
   * 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 (*end == '/') {

  		/* 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;

  	if (IS_ROOT(path->dentry))

  		return ERR_PTR(-ESTALE);

  	mnt = ERR_PTR(-ENOMEM);

  	fh = nfs_alloc_fhandle();
  	fattr = nfs_alloc_fattr();
  	if (fh == NULL || fattr == NULL)

  		goto out;

  	mnt = server->nfs_client->rpc_ops->submount(server, path->dentry, fh, fattr);

  	if (IS_ERR(mnt))

  		goto out;

  	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);

  	return mnt;

  }

  static int

  nfs_namespace_getattr(const struct path *path, struct kstat *stat,
  			u32 request_mask, unsigned int query_flags)

  {

  	if (NFS_FH(d_inode(path->dentry))->size != 0)
  		return nfs_getattr(path, stat, request_mask, query_flags);
  	generic_fillattr(d_inode(path->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_submount(mountdata->dentry, &nfs_xdev_fs_type, 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;

  	char *page = (char *) __get_free_page(GFP_USER);
  	char *devname;

  	if (page == NULL)

  		return ERR_PTR(-ENOMEM);

  	devname = nfs_devname(dentry, page, PAGE_SIZE);

  	if (IS_ERR(devname))

  		mnt = ERR_CAST(devname);

  	else
  		mnt = nfs_do_clone_mount(NFS_SB(dentry->d_sb), devname, &mountdata);

  	free_page((unsigned long)page);

  	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);