linux-kernel - Re: [PATCH net-next v4 2/9] net: create a dummy net

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Date: Wed, 10 Apr 2024 05:45:41 -0700
From: Breno Leitao <leitao@...ian.org>
To: Ido Schimmel <idosch@...sch.org>
Cc: aleksander.lobakin@...el.com, kuba@...nel.org, davem@...emloft.net,
	pabeni@...hat.com, edumazet@...gle.com, elder@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, nbd@....name,
	sean.wang@...iatek.com, Mark-MC.Lee@...iatek.com,
	lorenzo@...nel.org, taras.chornyi@...ision.eu,
	ath11k@...ts.infradead.org, ath10k@...ts.infradead.org,
	linux-wireless@...r.kernel.org, geomatsi@...il.com,
	kvalo@...nel.org, quic_jjohnson@...cinc.com, leon@...nel.org,
	dennis.dalessandro@...nelisnetworks.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	bpf@...r.kernel.org, Jiri Pirko <jiri@...nulli.us>,
	Simon Horman <horms@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	amcohen@...dia.com
Subject: Re: [PATCH net-next v4 2/9] net: create a dummy net_device allocator

On Wed, Apr 10, 2024 at 02:10:04PM +0300, Ido Schimmel wrote:
> On Tue, Apr 09, 2024 at 05:57:16AM -0700, Breno Leitao wrote:
> > It is impossible to use init_dummy_netdev together with alloc_netdev()
> > as the 'setup' argument.
> > 
> > This is because alloc_netdev() initializes some fields in the net_device
> > structure, and later init_dummy_netdev() memzero them all. This causes
> > some problems as reported here:
> > 
> > 	https://lore.kernel.org/all/20240322082336.49f110cc@kernel.org/
> > 
> > Split the init_dummy_netdev() function in two. Create a new function called
> > init_dummy_netdev_core() that does not memzero the net_device structure.
> > Then have init_dummy_netdev() memzero-ing and calling
> > init_dummy_netdev_core(), keeping the old behaviour.
> > 
> > init_dummy_netdev_core() is the new function that could be called as an
> > argument for alloc_netdev().
> > 
> > Also, create a helper to allocate and initialize dummy net devices,
> > leveraging init_dummy_netdev_core() as the setup argument. This function
> > basically simplify the allocation of dummy devices, by allocating and
> > initializing it. Freeing the device continue to be done through
> > free_netdev()
> > 
> > Suggested-by: Jakub Kicinski <kuba@...nel.org>
> > Signed-off-by: Breno Leitao <leitao@...ian.org>
> 
> Reviewed-by: Ido Schimmel <idosch@...dia.com>
> 
> We were about to submit another user of init_dummy_netdev() when I
> noticed this patch. Converted the code to use alloc_netdev_dummy() [1]
> and it seems to be working fine. Will submit after your patch is
> accepted.

Thanks. It seems that this patch is close to get accepted. Let's see...

> See a few minor comments below.
> 
> [...]
> 
> > +/**
> > + *	init_dummy_netdev	- init a dummy network device for NAPI
> > + *	@dev: device to init
> > + *
> > + *	This takes a network device structure and initialize the minimum
> 
> s/initialize/initializes/
> 
> > + *	amount of fields so it can be used to schedule NAPI polls without
> > + *	registering a full blown interface. This is to be used by drivers
> > + *	that need to tie several hardware interfaces to a single NAPI
> > + *	poll scheduler due to HW limitations.
> > + */
> > +void init_dummy_netdev(struct net_device *dev)
> > +{
> > +	/* Clear everything. Note we don't initialize spinlocks
> > +	 * are they aren't supposed to be taken by any of the
> 
> I assume you meant s/are/as/ ?

Thanks for the feedback, I agree with all of them.

Since these lines were not introduced by this patch, and this patch is
just moving code (and comments) around, I would add a new patch to the
patch series fixing the grammar errors.