netdev - Re: [PATCH net-next v3] net: Add sysfs atttribute for max

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Message-ID: <CANn89iJf68+GZ-myjkiZ40SJY1egD3-qYhVeZOdi=6TB13aE4w@mail.gmail.com>
Date: Thu, 9 May 2024 12:01:41 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Shradha Gupta <shradhagupta@...ux.microsoft.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Jonathan Corbet <corbet@....net>, Haiyang Zhang <haiyangz@...rosoft.com>, 
	Randy Dunlap <rdunlap@...radead.org>, Johannes Berg <johannes.berg@...el.com>, 
	Breno Leitao <leitao@...ian.org>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	Shradha Gupta <shradhagupta@...rosoft.com>
Subject: Re: [PATCH net-next v3] net: Add sysfs atttribute for max_mtu

On Thu, May 9, 2024 at 11:11 AM Shradha Gupta
<shradhagupta@...ux.microsoft.com> wrote:
>
> For drivers like MANA, max_mtu value is populated with the value of
> maximum MTU that the underlying hardware can support.
> Exposing this attribute as sysfs param, would be helpful in debugging
> and customization of config issues with such drivers.
>
> Signed-off-by: Shradha Gupta <shradhagupta@...ux.microsoft.com>
> Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>
> ---
>  Changes in v3:
>  * Removed the min_mtu sysfs attribute as it was not needed
>  * Improved the commit message to explain the need for the changes
>  * Seperated this patch from other mana attributes requirements.
> ---
>  Documentation/ABI/testing/sysfs-class-net | 8 ++++++++
>  net/core/net-sysfs.c                      | 2 ++
>  2 files changed, 10 insertions(+)


Sorry, this is a NACK from my side.

Adding sysfs attributes is costly for setups adding/deleting many
netns/devices per second.

RTNL already provides this value.

net/core/rtnetlink.c:1850:          nla_put_u32(skb, IFLA_MAX_MTU,
READ_ONCE(dev->max_mtu)) ||