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Message-Id: <20231216010431.84776-1-gsmecher@threespeedlogic.com>
Date: Fri, 15 Dec 2023 17:04:31 -0800
From: Graeme Smecher <gsmecher@...eespeedlogic.com>
To: David Ahern <dsahern@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
netdev@...r.kernel.org,
claudiu.beznea@...on.dev,
nicolas.ferre@...rochip.com,
mdf@...nel.org,
Graeme Smecher <gsmecher@...eespeedlogic.com>
Subject: [PATCH] RFC: net: ipconfig: temporarily bring interface down when changing MTU.
Several network drivers (sh_eth, macb_main, nixge, sundance) only allow
the MTU to be changed when the interface is down, because their buffer
allocations are performed during ndo_open() and calculated using a
specific MTU.
Kick-tested using QEMU (rtl8139, e1000).
Tested-by: Graeme Smecher <gsmecher@...eespeedlogic.com>
---
net/ipv4/ipconfig.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/ipconfig.c b/net/ipv4/ipconfig.c
index c56b6fe6f0d7..69c2a41393a0 100644
--- a/net/ipv4/ipconfig.c
+++ b/net/ipv4/ipconfig.c
@@ -396,9 +396,21 @@ static int __init ic_setup_if(void)
*/
if (ic_dev_mtu != 0) {
rtnl_lock();
- if ((err = dev_set_mtu(ic_dev->dev, ic_dev_mtu)) < 0)
- pr_err("IP-Config: Unable to set interface mtu to %d (%d)\n",
- ic_dev_mtu, err);
+ /* Some Ethernet adapters only allow MTU to change when down. */
+ if((err = dev_change_flags(ic_dev->dev, ic_dev->dev->flags | IFF_UP, NULL)))
+ pr_err("IP-Config: About to set MTU, but failed to "
+ "bring interface %s down! (%d)\n",
+ ic_dev->dev->name, err);
+ else {
+ if ((err = dev_set_mtu(ic_dev->dev, ic_dev_mtu)) < 0)
+ pr_err("IP-Config: Unable to set interface mtu to %d (%d)\n",
+ ic_dev_mtu, err);
+
+ if((err = dev_change_flags(ic_dev->dev, ic_dev->dev->flags | IFF_UP, NULL)))
+ pr_err("IP-Config: Trying to set MTU, but unable "
+ "to bring interface %s back up! (%d)\n",
+ ic_dev->dev->name, err);
+ }
rtnl_unlock();
}
return 0;
--
2.39.2
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