/*
   * 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
   *
   */
  
  static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
  {
  	hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
  }
  
  void v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
  {
  	spin_lock(&dentry->d_lock);
  	__add_fid(dentry, fid);
  	spin_unlock(&dentry->d_lock);
  }
  
  /**
   * 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, kuid_t uid, int any)
  {
  	struct p9_fid *fid, *ret;
  
  	p9_debug(P9_DEBUG_VFS, " dentry: %s (%p) uid %d any %d
  ",
  		 dentry->d_name.name, dentry, from_kuid(&init_user_ns, uid),
  		 any);
  	ret = NULL;
  	/* we'll recheck under lock if there's anything to look in */
  	if (dentry->d_fsdata) {
  		struct hlist_head *h = (struct hlist_head *)&dentry->d_fsdata;
  		spin_lock(&dentry->d_lock);
  		hlist_for_each_entry(fid, h, dlist) {
  			if (any || uid_eq(fid->uid, uid)) {
  				ret = fid;
  				break;
  			}
  		}
  		spin_unlock(&dentry->d_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,
  					       kuid_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)) {
  		spin_lock(&dentry->d_lock);
  		if (d_unhashed(dentry)) {
  			spin_unlock(&dentry->d_lock);
  			p9_client_clunk(fid);
  			fid = ERR_PTR(-ENOENT);
  		} else {
  			__add_fid(dentry, fid);
  			spin_unlock(&dentry->d_lock);
  		}
  	}
  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)
  {
  	kuid_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 = INVALID_UID;
  		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, kuid_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, GLOBAL_ROOT_UID);
  	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;
  }