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

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Message-ID: <Z4bupHBw-KgnnKWe@LQ3V64L9R2>
Date: Tue, 14 Jan 2025 15:09:24 -0800
From: Joe Damato <jdamato@...tly.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
	pabeni@...hat.com, andrew+netdev@...n.ch, horms@...nel.org
Subject: Re: [PATCH net-next 04/11] net: add netdev->up protected by
 netdev_lock()

On Mon, Jan 13, 2025 at 07:51:10PM -0800, Jakub Kicinski 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>
> ---
>  include/linux/netdevice.h | 13 ++++++++++++-
>  net/core/dev.h            | 12 ++++++++++++
>  net/core/dev.c            |  4 ++--
>  3 files changed, 26 insertions(+), 3 deletions(-)

Reviewed-by: Joe Damato <jdamato@...tly.com>