netdev - Re: [PATCH net-next 04/11] net: add netdev->up protected by netdev

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Message-ID: <CANn89iKMMhw94mi8sRWrXz3+zLVUUqe4EGum7t64AFmq=-Hszw@mail.gmail.com>
Date: Tue, 14 Jan 2025 14:08:15 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, pabeni@...hat.com, 
	andrew+netdev@...n.ch, horms@...nel.org, jdamato@...tly.com
Subject: Re: [PATCH net-next 04/11] net: add netdev->up protected by netdev_lock()

On Tue, Jan 14, 2025 at 4:51 AM Jakub Kicinski <kuba@...nel.org> wrote:
>
> Some uAPI (netdev netlink) hide net_device's sub-objects while
> the interface is down to ensure uniform behavior across drivers.
> To remove the rtnl_lock dependency from those uAPIs we need a way
> to safely tell if the device is down or up.
>
> Add an indication of whether device is open or closed, protected
> by netdev->lock. The semantics are the same as IFF_UP, but taking
> netdev_lock around every write to ->flags would be a lot of code
> churn.
>
> We don't want to blanket the entire open / close path by netdev_lock,
> because it will prevent us from applying it to specific structures -
> core helpers won't be able to take that lock from any function
> called by the drivers on open/close paths.
>
> So the state of the flag is "pessimistic", as in it may report false
> negatives, but never false positives.
>
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>