netdev - Re: [PATCH wpan-next 0/2] ieee802154: Beaconing support

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Message-ID: <CAK-6q+h6Xfa3x2XMjhgrw15LyQDGtfR7f+qgQDkSarteKqWaZA@mail.gmail.com>
Date:   Thu, 26 Jan 2023 20:31:37 -0500
From:   Alexander Aring <aahringo@...hat.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        David Girault <david.girault@...vo.com>,
        Romuald Despres <romuald.despres@...vo.com>,
        Frederic Blain <frederic.blain@...vo.com>,
        Nicolas Schodet <nico@...fr.eu.org>,
        Guilhem Imberton <guilhem.imberton@...vo.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH wpan-next 0/2] ieee802154: Beaconing support

Hi,

On Thu, Jan 26, 2023 at 8:29 PM Alexander Aring <aahringo@...hat.com> wrote:
>
> Hi,
>
> On Wed, Jan 25, 2023 at 5:00 AM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> >
> > Hi Alexander,
> >
> > alex.aring@...il.com wrote on Tue, 24 Jan 2023 21:31:33 -0500:
> >
> > > Hi,
> > >
> > > On Tue, Jan 24, 2023 at 5:08 AM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> > > >
> > > > Hi Alexander,
> > > >
> > > > aahringo@...hat.com wrote on Mon, 23 Jan 2023 09:02:48 -0500:
> > > >
> > > > > Hi,
> > > > >
> > > > > On Mon, Jan 23, 2023 at 9:01 AM Alexander Aring <aahringo@...hat.com> wrote:
> > > > > >
> > > > > > Hi,
> > > > > >
> > > > > > On Wed, Jan 18, 2023 at 4:21 AM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> > > > > > >
> > > > > > > Hi Alexander,
> > > > > > >
> > > > > > > aahringo@...hat.com wrote on Sun, 15 Jan 2023 20:54:02 -0500:
> > > > > > >
> > > > > > > > Hi,
> > > > > > > >
> > > > > > > > On Fri, Jan 6, 2023 at 6:33 AM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> > > > > > > > >
> > > > > > > > > Scanning being now supported, we can eg. play with hwsim to verify
> > > > > > > > > everything works as soon as this series including beaconing support gets
> > > > > > > > > merged.
> > > > > > > > >
> > > > > > > >
> > > > > > > > I am not sure if a beacon send should be handled by an mlme helper
> > > > > > > > handling as this is a different use-case and the user does not trigger
> > > > > > > > an mac command and is waiting for some reply and a more complex
> > > > > > > > handling could be involved. There is also no need for hotpath xmit
> > > > > > > > handling is disabled during this time. It is just an async messaging
> > > > > > > > in some interval and just "try" to send it and don't care if it fails,
> > > > > > > > or? For mac802154 therefore I think we should use the dev_queue_xmit()
> > > > > > > > function to queue it up to send it through the hotpath?
> > > > > > > >
> > > > > > > > I can ack those patches, it will work as well. But I think we should
> > > > > > > > switch at some point to dev_queue_xmit(). It should be simple to
> > > > > > > > switch it. Just want to mention there is a difference which will be
> > > > > > > > there in mac-cmds like association.
> > > > > > >
> > > > > > > I see what you mean. That's indeed true, we might just switch to
> > > > > > > a less constrained transmit path.
> > > > > > >
> > > > > >
> > > > > > I would define the difference in bypass qdisc or not. Whereas the
> > > > > > qdisc can drop or delay transmitting... For me, the qdisc is currently
> > > > > > in a "works for now" state.
> > > > >
> > > > > probably also bypass other hooks like tc, etc. :-/ Not sure if we want that.
> > > >
> > > > Actually, IIUC, we no longer want to go through the entire net stack.
> > > > We still want to bypass it but without stopping/flushing the full
> > > > queue like with an mlme transmission, so what about using
> > > > ieee802154_subif_start_xmit() instead of dev_queue_xmit()? I think it
> > > > is more appropriate.
> > >
> > > I do not understand, what do we currently do with mlme ops via the
> > > ieee802154_subif_start_xmit() function, or? So we bypass everything
> > > from dev_queue_xmit() until do_xmit() netdev callback.
> >
> > Yes, that's the plan. We don't want any of the net stack features when
> > sending beacons.
> >
> > > I think it is fine, also I think "mostly" only dataframes should go
> > > through dev_queue_xmit(). With a HardMAC transceiver we would have
> > > control about "mostly" other frames than data either. So we should do
> > > everything with mlme-ops do what the spec says (to match up with
> > > HardMAC behaviour?) and don't allow common net hooks/etc. to change
> > > this behaviour?
> >
> > To summarize:
> > - Data frames -> should go through dev_queue_xmit()
>
> there are exceptions... e.g. AF_PACKET raw sockets can build whatever
> it wants (but it will probably not being supported by HardMAC
> transceivers) and send it out. There is no real control about it. So
> mostly I would agree here.
>

with "no real control" I mean the user needs to know what it's doing
there and maybe the user just wants to play around e.g. monitor
interface sending, whereas a monitor does not have an address being
set up.

- Alex