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Message-ID: <20231215193024.02819d85@hermes.local>
Date: Fri, 15 Dec 2023 19:30:24 -0800
From: Stephen Hemminger <stephen@...workplumber.org>
To: Graeme Smecher <gsmecher@...eespeedlogic.com>
Cc: David Ahern <dsahern@...nel.org>, "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
Subject: Re: [PATCH] RFC: net: ipconfig: temporarily bring interface down
when changing MTU.
On Fri, 15 Dec 2023 17:04:31 -0800
Graeme Smecher <gsmecher@...eespeedlogic.com> wrote:
> 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. */
Check if interface was already down first.
> + if((err = dev_change_flags(ic_dev->dev, ic_dev->dev->flags | IFF_UP, NULL)))
Please do not combine function call with err test. Surprised checkpatch doesn't complain about hat.
> + pr_err("IP-Config: About to set MTU, but failed to "
> + "bring interface %s down! (%d)\n",
Don't break lines in error messages.
> + 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;
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