/*
   * V9FS FID Management
   *

   *  Copyright (C) 2007 by Latchesar Ionkov <lucho@ionkov.net>

   *  Copyright (C) 2005, 2006 by Eric Van Hensbergen <ericvh@gmail.com>

   *
   *  This program is free software; you can redistribute it and/or modify

   *  it under the terms of the GNU General Public License version 2
   *  as published by the Free Software Foundation.

   *
   *  This program is distributed in the hope that it will be useful,
   *  but WITHOUT ANY WARRANTY; without even the implied warranty of
   *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   *  GNU General Public License for more details.
   *
   *  You should have received a copy of the GNU General Public License
   *  along with this program; if not, write to:
   *  Free Software Foundation
   *  51 Franklin Street, Fifth Floor
   *  Boston, MA  02111-1301  USA
   *
   */

  #include <linux/module.h>
  #include <linux/errno.h>
  #include <linux/fs.h>

  #include <linux/slab.h>

  #include <linux/sched.h>

  #include <linux/idr.h>

  #include <net/9p/9p.h>
  #include <net/9p/client.h>

  #include "v9fs.h"

  #include "v9fs_vfs.h"

  #include "fid.h"
  
  /**

   * v9fs_fid_add - add a fid to a dentry
   * @dentry: dentry that the fid is being added to

   * @fid: fid to add

   *
   */

  int v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)

  {

  	struct v9fs_dentry *dent;

  	p9_debug(P9_DEBUG_VFS, "fid %d dentry %s
  ",
  		 fid->fid, dentry->d_name.name);

  	dent = dentry->d_fsdata;
  	if (!dent) {
  		dent = kmalloc(sizeof(struct v9fs_dentry), GFP_KERNEL);
  		if (!dent)
  			return -ENOMEM;

  		spin_lock_init(&dent->lock);
  		INIT_LIST_HEAD(&dent->fidlist);
  		dentry->d_fsdata = dent;

  	}

  	spin_lock(&dent->lock);
  	list_add(&fid->dlist, &dent->fidlist);
  	spin_unlock(&dent->lock);

  	return 0;

  }
  
  /**

   * v9fs_fid_find - retrieve a fid that belongs to the specified uid

   * @dentry: dentry to look for fid in

   * @uid: return fid that belongs to the specified user
   * @any: if non-zero, return any fid associated with the dentry

   *
   */

  static struct p9_fid *v9fs_fid_find(struct dentry *dentry, u32 uid, int any)

  {

  	struct v9fs_dentry *dent;

  	struct p9_fid *fid, *ret;

  	p9_debug(P9_DEBUG_VFS, " dentry: %s (%p) uid %d any %d
  ",
  		 dentry->d_name.name, dentry, uid, any);

  	dent = (struct v9fs_dentry *) dentry->d_fsdata;
  	ret = NULL;
  	if (dent) {
  		spin_lock(&dent->lock);
  		list_for_each_entry(fid, &dent->fidlist, dlist) {
  			if (any || fid->uid == uid) {
  				ret = fid;
  				break;
  			}
  		}
  		spin_unlock(&dent->lock);
  	}

  	return ret;

  }

  /*
   * We need to hold v9ses->rename_sem as long as we hold references
   * to returned path array. Array element contain pointers to
   * dentry names.
   */
  static int build_path_from_dentry(struct v9fs_session_info *v9ses,
  				  struct dentry *dentry, char ***names)
  {
  	int n = 0, i;
  	char **wnames;
  	struct dentry *ds;
  
  	for (ds = dentry; !IS_ROOT(ds); ds = ds->d_parent)
  		n++;
  
  	wnames = kmalloc(sizeof(char *) * n, GFP_KERNEL);
  	if (!wnames)
  		goto err_out;
  
  	for (ds = dentry, i = (n-1); i >= 0; i--, ds = ds->d_parent)
  		wnames[i] = (char  *)ds->d_name.name;
  
  	*names = wnames;
  	return n;
  err_out:
  	return -ENOMEM;
  }

  static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
  					       uid_t uid, int any)

  {

  	struct dentry *ds;

  	char **wnames, *uname;

  	int i, n, l, clone, access;
  	struct v9fs_session_info *v9ses;
  	struct p9_fid *fid, *old_fid = NULL;

  	v9ses = v9fs_dentry2v9ses(dentry);

  	access = v9ses->flags & V9FS_ACCESS_MASK;

  	fid = v9fs_fid_find(dentry, uid, any);
  	if (fid)
  		return fid;

  	/*
  	 * we don't have a matching fid. To do a TWALK we need
  	 * parent fid. We need to prevent rename when we want to
  	 * look at the parent.
  	 */
  	down_read(&v9ses->rename_sem);

  	ds = dentry->d_parent;
  	fid = v9fs_fid_find(ds, uid, any);

  	if (fid) {
  		/* Found the parent fid do a lookup with that */
  		fid = p9_client_walk(fid, 1, (char **)&dentry->d_name.name, 1);
  		goto fid_out;
  	}
  	up_read(&v9ses->rename_sem);

  	/* start from the root and try to do a lookup */
  	fid = v9fs_fid_find(dentry->d_sb->s_root, uid, any);
  	if (!fid) {
  		/* the user is not attached to the fs yet */
  		if (access == V9FS_ACCESS_SINGLE)
  			return ERR_PTR(-EPERM);

  		if (v9fs_proto_dotu(v9ses) || v9fs_proto_dotl(v9ses))
  				uname = NULL;
  		else
  			uname = v9ses->uname;

  		fid = p9_client_attach(v9ses->clnt, NULL, uname, uid,
  				       v9ses->aname);
  		if (IS_ERR(fid))
  			return fid;

  		v9fs_fid_add(dentry->d_sb->s_root, fid);
  	}
  	/* If we are root ourself just return that */
  	if (dentry->d_sb->s_root == dentry)

  		return fid;

  	/*
  	 * Do a multipath walk with attached root.
  	 * When walking parent we need to make sure we
  	 * don't have a parallel rename happening
  	 */
  	down_read(&v9ses->rename_sem);
  	n  = build_path_from_dentry(v9ses, dentry, &wnames);
  	if (n < 0) {
  		fid = ERR_PTR(n);
  		goto err_out;
  	}

  	clone = 1;
  	i = 0;
  	while (i < n) {
  		l = min(n - i, P9_MAXWELEM);

  		/*
  		 * We need to hold rename lock when doing a multipath
  		 * walk to ensure none of the patch component change
  		 */

  		fid = p9_client_walk(fid, l, &wnames[i], clone);

  		if (IS_ERR(fid)) {

  			if (old_fid) {
  				/*
  				 * If we fail, clunk fid which are mapping
  				 * to path component and not the last component
  				 * of the path.
  				 */
  				p9_client_clunk(old_fid);
  			}

  			kfree(wnames);

  			goto err_out;

  		}

  		old_fid = fid;

  		i += l;
  		clone = 0;
  	}

  	kfree(wnames);

  fid_out:

  	if (!IS_ERR(fid))
  		v9fs_fid_add(dentry, fid);

  err_out:
  	up_read(&v9ses->rename_sem);

  	return fid;

  }

  /**
   * v9fs_fid_lookup - lookup for a fid, try to walk if not found
   * @dentry: dentry to look for fid in
   *
   * Look for a fid in the specified dentry for the current user.
   * If no fid is found, try to create one walking from a fid from the parent
   * dentry (if it has one), or the root dentry. If the user haven't accessed
   * the fs yet, attach now and walk from the root.
   */
  
  struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
  {
  	uid_t uid;
  	int  any, access;
  	struct v9fs_session_info *v9ses;

  	v9ses = v9fs_dentry2v9ses(dentry);

  	access = v9ses->flags & V9FS_ACCESS_MASK;
  	switch (access) {
  	case V9FS_ACCESS_SINGLE:
  	case V9FS_ACCESS_USER:
  	case V9FS_ACCESS_CLIENT:
  		uid = current_fsuid();
  		any = 0;
  		break;
  
  	case V9FS_ACCESS_ANY:
  		uid = v9ses->uid;
  		any = 1;
  		break;
  
  	default:
  		uid = ~0;
  		any = 0;
  		break;
  	}
  	return v9fs_fid_lookup_with_uid(dentry, uid, any);
  }

  struct p9_fid *v9fs_fid_clone(struct dentry *dentry)
  {
  	struct p9_fid *fid, *ret;
  
  	fid = v9fs_fid_lookup(dentry);
  	if (IS_ERR(fid))
  		return fid;
  
  	ret = p9_client_walk(fid, 0, NULL, 1);
  	return ret;
  }

  static struct p9_fid *v9fs_fid_clone_with_uid(struct dentry *dentry, uid_t uid)
  {
  	struct p9_fid *fid, *ret;
  
  	fid = v9fs_fid_lookup_with_uid(dentry, uid, 0);
  	if (IS_ERR(fid))
  		return fid;
  
  	ret = p9_client_walk(fid, 0, NULL, 1);
  	return ret;
  }

  
  struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
  {

  	int err;

  	struct p9_fid *fid;

  	fid = v9fs_fid_clone_with_uid(dentry, 0);

  	if (IS_ERR(fid))
  		goto error_out;
  	/*
  	 * writeback fid will only be used to write back the
  	 * dirty pages. We always request for the open fid in read-write
  	 * mode so that a partial page write which result in page
  	 * read can work.

  	 */

  	err = p9_client_open(fid, O_RDWR);

  	if (err < 0) {
  		p9_client_clunk(fid);
  		fid = ERR_PTR(err);
  		goto error_out;
  	}
  error_out:
  	return fid;
  }