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Message-ID: <aa341e85-6a3f-4d4b-a2a7-b19bf0c9ba2f@kernel.org>
Date: Sat, 16 Dec 2023 11:12:46 -0700
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Subject: Re: [PATCH] RFC: net: ipconfig: temporarily bring interface down when
 changing MTU.
Content-Language: en-US
To: Stephen Hemminger <stephen@networkplumber.org>,
 Graeme Smecher <gsmecher@threespeedlogic.com>
Cc: "David S. Miller" <davem@davemloft.net>,
 Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
 Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
 claudiu.beznea@tuxon.dev, nicolas.ferre@microchip.com, mdf@kernel.org
References: <58519bfa-260c-4745-a145-fdca89b4e9d1@kernel.org>
 <20231216010431.84776-1-gsmecher@threespeedlogic.com>
 <20231215193024.02819d85@hermes.local>
From: David Ahern <dsahern@kernel.org>
In-Reply-To: <20231215193024.02819d85@hermes.local>
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On 12/15/23 7:30 PM, Stephen Hemminger wrote:
>> 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. */
> Check if interface was already down first.


it is; see ic_open_devs. ic_close_devs will bring down all interfaces
not configured by ipconfig.