/*
   *  fs/cifs/dns_resolve.c
   *
   *   Copyright (c) 2007 Igor Mammedov
   *   Author(s): Igor Mammedov (niallain@gmail.com)
   *              Steve French (sfrench@us.ibm.com)
   *              Wang Lei (wang840925@gmail.com)
   *		David Howells (dhowells@redhat.com)
   *
   *   Contains the CIFS DFS upcall routines used for hostname to
   *   IP address translation.
   *
   *   This library is free software; you can redistribute it and/or modify
   *   it under the terms of the GNU Lesser General Public License as published
   *   by the Free Software Foundation; either version 2.1 of the License, or
   *   (at your option) any later version.
   *
   *   This library 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 Lesser General Public License for more details.
   *
   *   You should have received a copy of the GNU Lesser General Public License
   *   along with this library; if not, write to the Free Software
   *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
   */
  
  #include <linux/slab.h>
  #include <linux/dns_resolver.h>
  #include "dns_resolve.h"
  #include "cifsglob.h"
  #include "cifsproto.h"
  #include "cifs_debug.h"
  
  /**
   * dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
   * @unc: UNC path specifying the server (with '/' as delimiter)
   * @ip_addr: Where to return the IP address.
   *
   * The IP address will be returned in string form, and the caller is
   * responsible for freeing it.
   *
   * Returns length of result on success, -ve on error.
   */
  int
  dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
  {
  	struct sockaddr_storage ss;
  	const char *hostname, *sep;
  	char *name;
  	int len, rc;
  
  	if (!ip_addr || !unc)
  		return -EINVAL;
  
  	len = strlen(unc);
  	if (len < 3) {
  		cifs_dbg(FYI, "%s: unc is too short: %s
  ", __func__, unc);
  		return -EINVAL;
  	}
  
  	/* Discount leading slashes for cifs */
  	len -= 2;
  	hostname = unc + 2;
  
  	/* Search for server name delimiter */
  	sep = memchr(hostname, '/', len);
  	if (sep)
  		len = sep - hostname;
  	else
  		cifs_dbg(FYI, "%s: probably server name is whole unc: %s
  ",
  			 __func__, unc);
  
  	/* Try to interpret hostname as an IPv4 or IPv6 address */
  	rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
  	if (rc > 0)
  		goto name_is_IP_address;
  
  	/* Perform the upcall */
  	rc = dns_query(NULL, hostname, len, NULL, ip_addr, NULL);
  	if (rc < 0)
  		cifs_dbg(FYI, "%s: unable to resolve: %*.*s
  ",
  			 __func__, len, len, hostname);
  	else
  		cifs_dbg(FYI, "%s: resolved: %*.*s to %s
  ",
  			 __func__, len, len, hostname, *ip_addr);
  	return rc;
  
  name_is_IP_address:
  	name = kmalloc(len + 1, GFP_KERNEL);
  	if (!name)
  		return -ENOMEM;
  	memcpy(name, hostname, len);
  	name[len] = 0;
  	cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %s
  ",
  		 __func__, name);
  	*ip_addr = name;
  	return 0;
  }