netdev - Re: [PATCH] RFC: net: ipconfig: temporarily bring interface down when changing MTU.

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Date: Tue, 19 Dec 2023 12:33:58 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Graeme Smecher <gsmecher@...eespeedlogic.com>, David Ahern
	 <dsahern@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>,  Jakub Kicinski <kuba@...nel.org>,
 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, 2023-12-15 at 17:04 -0800, Graeme Smecher 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.

I think we have to address that in the relevant device drivers. This
could cause significant regressions: changing the MTU may causes the
device to stay down afterwards - if the device fails to re-initialize.

That even for drivers that before failed gracefully.

Instead, at the device level, the driver could allocate in advance the
new ring, and restore the previous one if the allocation fails, always
leaving the device in a consistent status.

Cheers,

Paolo