[PATCH] Configurable tap interface MTU

[PATCH] Configurable tap interface MTU

[Ed Swierk]

[-- Attachment #1: Type: text/plain, Size: 422 bytes --]

This patch makes it possible to change the MTU on a tap interface.
Increasing the MTU beyond the 1500-byte default is useful for
applications that interoperate with Ethernet devices supporting jumbo
frames.

The patch caps the MTU somewhat arbitrarily at 16000 bytes. This is
slightly lower than the value used by the e1000 driver, so it seems
like a safe upper limit.

Signed-off-by: Ed Swierk <eswierk@arastra.com>

---

[-- Attachment #2: tap-change-mtu.patch --]
[-- Type: application/octet-stream, Size: 931 bytes --]

Index: linux-2.6.22.6/drivers/net/tun.c
===================================================================
--- linux-2.6.22.6.orig/drivers/net/tun.c
+++ linux-2.6.22.6/drivers/net/tun.c
@@ -171,6 +171,18 @@ tun_net_mclist(struct net_device *dev)
 	}
 }
 
+#define MIN_MTU 68
+#define MAX_MTU 16000
+
+static int
+tun_net_change_mtu(struct net_device *dev, int new_mtu)
+{
+	if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
+		return -EINVAL;
+	dev->mtu = new_mtu;
+	return 0;
+}
+
 static struct net_device_stats *tun_net_stats(struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
@@ -200,6 +212,7 @@ static void tun_net_init(struct net_devi
 		dev->set_multicast_list = tun_net_mclist;
 
 		ether_setup(dev);
+		dev->change_mtu = tun_net_change_mtu;
 
 		/* random address already created for us by tun_set_iff, use it */
 		memcpy(dev->dev_addr, tun->dev_addr, min(sizeof(tun->dev_addr), sizeof(dev->dev_addr)) );

Re: [PATCH] Configurable tap interface MTU

[Rick Jones]

Ed Swierk wrote:
> This patch makes it possible to change the MTU on a tap interface.
> Increasing the MTU beyond the 1500-byte default is useful for
> applications that interoperate with Ethernet devices supporting jumbo
> frames.
> 
> The patch caps the MTU somewhat arbitrarily at 16000 bytes. This is
> slightly lower than the value used by the e1000 driver, so it seems
> like a safe upper limit.

FWIW the OFED 1.2 bits take the MTU of IPoIB up to 65520 bytes :)

rick jones

Re: [PATCH] Configurable tap interface MTU

[Herbert Xu]

Ed Swierk <eswierk@arastra.com> wrote:
> 
> The patch caps the MTU somewhat arbitrarily at 16000 bytes. This is
> slightly lower than the value used by the e1000 driver, so it seems
> like a safe upper limit.

Please make it 65535 without an Ethernet header and 65521
with an Ethernet header.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: [PATCH] Configurable tap interface MTU

[Ed Swierk]

[-- Attachment #1: Type: text/plain, Size: 404 bytes --]

On 9/11/07, Herbert Xu <herbert@gondor.apana.org.au> wrote:
> Please make it 65535 without an Ethernet header and 65521
> with an Ethernet header.

Here is a revised patch that allows MTUs up to 65535 for tap
interfaces and up to 65521 for tun interfaces.

(If I set the MTU to 65521 on a tun interface, ping complains "message
too long" when I send a 65521-byte packet; 65520 works okay, though.)

--Ed

[-- Attachment #2: tap-change-mtu.patch --]
[-- Type: application/octet-stream, Size: 1185 bytes --]

Index: linux-2.6.22.6/drivers/net/tun.c
===================================================================
--- linux-2.6.22.6.orig/drivers/net/tun.c
+++ linux-2.6.22.6/drivers/net/tun.c
@@ -171,6 +171,18 @@ tun_net_mclist(struct net_device *dev)
 	}
 }
 
+#define MIN_MTU 68
+#define MAX_MTU 65535
+
+static int
+tun_net_change_mtu(struct net_device *dev, int new_mtu)
+{
+	if (new_mtu < MIN_MTU || new_mtu + dev->hard_header_len > MAX_MTU)
+		return -EINVAL;
+	dev->mtu = new_mtu;
+	return 0;
+}
+
 static struct net_device_stats *tun_net_stats(struct net_device *dev)
 {
 	struct tun_struct *tun = netdev_priv(dev);
@@ -188,6 +200,7 @@ static void tun_net_init(struct net_devi
 		dev->hard_header_len = 0;
 		dev->addr_len = 0;
 		dev->mtu = 1500;
+		dev->change_mtu = tun_net_change_mtu;
 
 		/* Zero header length */
 		dev->type = ARPHRD_NONE;
@@ -200,6 +213,7 @@ static void tun_net_init(struct net_devi
 		dev->set_multicast_list = tun_net_mclist;
 
 		ether_setup(dev);
+		dev->change_mtu = tun_net_change_mtu;
 
 		/* random address already created for us by tun_set_iff, use it */
 		memcpy(dev->dev_addr, tun->dev_addr, min(sizeof(tun->dev_addr), sizeof(dev->dev_addr)) );

Re: [PATCH] Configurable tap interface MTU

[David Miller]

From: "Ed Swierk" <eswierk@arastra.com>
Date: Wed, 12 Sep 2007 09:54:35 -0700

> On 9/11/07, Herbert Xu <herbert@gondor.apana.org.au> wrote:
> > Please make it 65535 without an Ethernet header and 65521
> > with an Ethernet header.
> 
> Here is a revised patch that allows MTUs up to 65535 for tap
> interfaces and up to 65521 for tun interfaces.
> 
> (If I set the MTU to 65521 on a tun interface, ping complains "message
> too long" when I send a 65521-byte packet; 65520 works okay, though.)

Applied to net-2.6.24

Please provide a proper Signed-off-by: line and a full
changelog with every patch submission and revision in
the future.

Thanks.