netdev - Re: What is the purpose of dev->gflags?

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Message-ID: <41a58ead-9a14-c061-ee12-42050605deff@6wind.com>
Date:   Mon, 11 Apr 2022 18:10:49 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: What is the purpose of dev->gflags?


Le 11/04/2022 à 17:49, Vladimir Oltean a écrit :
> On Mon, Apr 11, 2022 at 05:43:01PM +0200, Nicolas Dichtel wrote:
>>
>> Le 11/04/2022 à 17:33, Vladimir Oltean a écrit :
>> [snip]
>>> Would you agree that the __dev_set_allmulti() -> __dev_notify_flags()
>>> call path is dead code? If it is, is there any problem it should be
>>> addressing which it isn't, or can we just delete it?
>> I probably miss your point, why is it dead code?
> 
> Because __dev_set_allmulti() doesn't update dev->gflags, it means
> dev->gflags == old_gflags. In turn, it means dev->gflags ^ old_gflags,
> passed to "gchanges" of __dev_notify_flags(), is 0.
I didn't take any assumptions on dev->gflags because two functions are called
with dev as parameter (dev_change_rx_flags() and dev_set_rx_mode()).
Even if __dev_notify_flags() is called with 0 for the last arg, it calls
notifiers. Thus, this is not "dead code".