[PATCH v3] ipconfig: add nameserver IPs to kernel-parameter ip=

[Christoph Fritz <chf.fritz@googlemail.com>]

On small systems (e.g. embedded ones) IP addresses are often configured
by bootloaders and get assigned to kernel via parameter "ip=".  If set to
"ip=dhcp", even nameserver entries from DHCP daemons are handled. These
entries exported in /proc/net/pnp are commonly linked by /etc/resolv.conf.

To configure nameservers for networks without DHCP, this patch adds option
<dns0-ip> and <dns1-ip> to kernel-parameter 'ip='.

Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Tested-by: Jan Weitzel <j.weitzel@phytec.de>
---
v2: - fix indent
v3: - fix docu: add new arguments to option "ip="
---
 Documentation/filesystems/nfs/nfsroot.txt |   10 ++++++-
 net/ipv4/ipconfig.c                       |   39 ++++++++++++++++++++++++++--
 2 files changed, 45 insertions(+), 4 deletions(-)

diff --git a/Documentation/filesystems/nfs/nfsroot.txt b/Documentation/filesystems/nfs/nfsroot.txt
index ffdd9d8..2d66ed6 100644
--- a/Documentation/filesystems/nfs/nfsroot.txt
+++ b/Documentation/filesystems/nfs/nfsroot.txt
@@ -78,7 +78,8 @@ nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
 			flags		= hard, nointr, noposix, cto, ac
 
 
-ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>
+ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:
+   <dns0-ip>:<dns1-ip>
 
   This parameter tells the kernel how to configure IP addresses of devices
   and also how to set up the IP routing table. It was originally called
@@ -158,6 +159,13 @@ ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>
 
                 Default: any
 
+  <dns0-ip>	IP address of first nameserver.
+		Value gets exported by /proc/net/pnp which is often linked
+		on embedded systems by /etc/resolv.conf.
+
+  <dns1-ip>	IP address of secound nameserver.
+		Same as above.
+
 
 nfsrootdebug
 
diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 67e8a6b..1c0e7e0 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -743,14 +743,22 @@ static void __init ic_bootp_init_ext(u8 *e)
 
 
 /*
- *  Initialize the DHCP/BOOTP mechanism.
+ *  Predefine Nameservers
  */
-static inline void __init ic_bootp_init(void)
+static inline void __init ic_nameservers_predef(void)
 {
 	int i;
 
 	for (i = 0; i < CONF_NAMESERVERS_MAX; i++)
 		ic_nameservers[i] = NONE;
+}
+
+/*
+ *  Initialize the DHCP/BOOTP mechanism.
+ */
+static inline void __init ic_bootp_init(void)
+{
+	ic_nameservers_predef();
 
 	dev_add_pack(&bootp_packet_type);
 }
@@ -1379,6 +1387,7 @@ static int __init ip_auto_config(void)
 	int retries = CONF_OPEN_RETRIES;
 #endif
 	int err;
+	unsigned int i;
 
 #ifdef CONFIG_PROC_FS
 	proc_net_fops_create(&init_net, "pnp", S_IRUGO, &pnp_seq_fops);
@@ -1499,7 +1508,15 @@ static int __init ip_auto_config(void)
 		&ic_servaddr, &root_server_addr, root_server_path);
 	if (ic_dev_mtu)
 		pr_cont(", mtu=%d", ic_dev_mtu);
-	pr_cont("\n");
+	for (i = 0; i < CONF_NAMESERVERS_MAX; i++)
+		if (ic_nameservers[i] != NONE) {
+			pr_info("     nameserver%u=%pI4",
+				i, &ic_nameservers[i]);
+			break;
+		}
+	for (i++; i < CONF_NAMESERVERS_MAX; i++)
+		if (ic_nameservers[i] != NONE)
+			pr_cont(", nameserver%u=%pI4\n", i, &ic_nameservers[i]);
 #endif /* !SILENT */
 
 	return 0;
@@ -1570,6 +1587,8 @@ static int __init ip_auto_config_setup(char *addrs)
 		return 1;
 	}
 
+	ic_nameservers_predef();
+
 	/* Parse string for static IP assignment.  */
 	ip = addrs;
 	while (ip && *ip) {
@@ -1613,6 +1632,20 @@ static int __init ip_auto_config_setup(char *addrs)
 					ic_enable = 0;
 				}
 				break;
+			case 7:
+				if (CONF_NAMESERVERS_MAX >= 1) {
+					ic_nameservers[0] = in_aton(ip);
+					if (ic_nameservers[0] == ANY)
+						ic_nameservers[0] = NONE;
+				}
+				break;
+			case 8:
+				if (CONF_NAMESERVERS_MAX >= 2) {
+					ic_nameservers[1] = in_aton(ip);
+					if (ic_nameservers[1] == ANY)
+						ic_nameservers[1] = NONE;
+				}
+				break;
 			}
 		}
 		ip = cp;
-- 
1.7.2.5