ipv4: teach ipconfig about the MTU option in DHCP

The DHCP spec allows the server to specify the MTU.  This can be useful
for netbooting with UDP-based NFS-root on a network using jumbo frames.
This patch allows the kernel IP autoconfiguration to handle this option
correctly.

It would be possible to use initramfs and add a script to set the MTU,
but that seems like a complicated solution if no initramfs is otherwise
necessary, and would bloat the kernel image more than this code would.

This patch was originally submitted to LKML in 2003 by Hans-Peter Jansen.

Signed-off-by: Chris Friesen <cfriesen@nortel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index 88bf051d0cbb4cd8989b44b8e894e6ab0ac60e53..f8d04c256454fe14c4bbd65689e174b7cf9bbc04 100644 (file)
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -160,6 +160,9 @@ static char user_dev_name[IFNAMSIZ] __initdata = { 0, };
 /* Protocols supported by available interfaces */
 static int ic_proto_have_if __initdata = 0;
 
+/* MTU for boot device */
+static int ic_dev_mtu __initdata = 0;
+
 #ifdef IPCONFIG_DYNAMIC
 static DEFINE_SPINLOCK(ic_recv_lock);
 static volatile int ic_got_reply __initdata = 0;    /* Proto(s) that replied */
@@ -286,7 +289,7 @@ set_sockaddr(struct sockaddr_in *sin, __be32 addr, __be16 port)
        sin->sin_port = port;
 }
 
-static int __init ic_dev_ioctl(unsigned int cmd, struct ifreq *arg)
+static int __init ic_devinet_ioctl(unsigned int cmd, struct ifreq *arg)
 {
        int res;
 
@@ -297,6 +300,17 @@ static int __init ic_dev_ioctl(unsigned int cmd, struct ifreq *arg)
        return res;
 }
 
+static int __init ic_dev_ioctl(unsigned int cmd, struct ifreq *arg)
+{
+       int res;
+
+       mm_segment_t oldfs = get_fs();
+       set_fs(get_ds());
+       res = dev_ioctl(&init_net, cmd, (struct ifreq __user *) arg);
+       set_fs(oldfs);
+       return res;
+}
+
 static int __init ic_route_ioctl(unsigned int cmd, struct rtentry *arg)
 {
        int res;
@@ -321,20 +335,31 @@ static int __init ic_setup_if(void)
        memset(&ir, 0, sizeof(ir));
        strcpy(ir.ifr_ifrn.ifrn_name, ic_dev->name);
        set_sockaddr(sin, ic_myaddr, 0);
-       if ((err = ic_dev_ioctl(SIOCSIFADDR, &ir)) < 0) {
+       if ((err = ic_devinet_ioctl(SIOCSIFADDR, &ir)) < 0) {
                printk(KERN_ERR "IP-Config: Unable to set interface address (%d).\n", err);
                return -1;
        }
        set_sockaddr(sin, ic_netmask, 0);
-       if ((err = ic_dev_ioctl(SIOCSIFNETMASK, &ir)) < 0) {
+       if ((err = ic_devinet_ioctl(SIOCSIFNETMASK, &ir)) < 0) {
                printk(KERN_ERR "IP-Config: Unable to set interface netmask (%d).\n", err);
                return -1;
        }
        set_sockaddr(sin, ic_myaddr | ~ic_netmask, 0);
-       if ((err = ic_dev_ioctl(SIOCSIFBRDADDR, &ir)) < 0) {
+       if ((err = ic_devinet_ioctl(SIOCSIFBRDADDR, &ir)) < 0) {
                printk(KERN_ERR "IP-Config: Unable to set interface broadcast address (%d).\n", err);
                return -1;
        }
+       /* Handle the case where we need non-standard MTU on the boot link (a network
+        * using jumbo frames, for instance).  If we can't set the mtu, don't error
+        * out, we'll try to muddle along.
+        */
+       if (ic_dev_mtu != 0) {
+               strcpy(ir.ifr_name, ic_dev->name);
+               ir.ifr_mtu = ic_dev_mtu;
+               if ((err = ic_dev_ioctl(SIOCSIFMTU, &ir)) < 0)
+                       printk(KERN_ERR "IP-Config: Unable to set interface mtu to %d (%d).\n",
+                                        ic_dev_mtu, err);
+       }
        return 0;
 }
 
@@ -623,6 +648,7 @@ ic_dhcp_init_options(u8 *options)
                        12,     /* Host name */
                        15,     /* Domain name */
                        17,     /* Boot path */
+                       26,     /* MTU */
                        40,     /* NIS domain name */
                };
 
@@ -798,6 +824,7 @@ static void __init ic_do_bootp_ext(u8 *ext)
 {
        u8 servers;
        int i;
+       u16 mtu;
 
 #ifdef IPCONFIG_DEBUG
        u8 *c;
@@ -837,6 +864,10 @@ static void __init ic_do_bootp_ext(u8 *ext)
                        if (!root_server_path[0])
                                ic_bootp_string(root_server_path, ext+1, *ext, sizeof(root_server_path));
                        break;
+               case 26:        /* Interface MTU */
+                       memcpy(&mtu, ext+1, sizeof(mtu));
+                       ic_dev_mtu = ntohs(mtu);
+                       break;
                case 40:        /* NIS Domain name (_not_ DNS) */
                        ic_bootp_string(utsname()->domainname, ext+1, *ext, __NEW_UTS_LEN);
                        break;
@@ -1403,6 +1434,8 @@ static int __init ip_auto_config(void)
        printk(",\n     bootserver=%pI4", &ic_servaddr);
        printk(", rootserver=%pI4", &root_server_addr);
        printk(", rootpath=%s", root_server_path);
+       if (ic_dev_mtu)
+               printk(", mtu=%d", ic_dev_mtu);
        printk("\n");
 #endif /* !SILENT */