netdev - Re: [PATCH wpan-next v3 2/4] net: ieee802154: Add support for inter PAN management

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Message-ID: <20220627104303.5392c7f6@xps-13>
Date:   Mon, 27 Jun 2022 10:43:03 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Alexander Aring <aahringo@...hat.com>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan - ML <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>,
        Network Development <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>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH wpan-next v3 2/4] net: ieee802154: Add support for inter
 PAN management

Hi Alexander,

aahringo@...hat.com wrote on Sat, 25 Jun 2022 22:29:08 -0400:

> Hi,
> 
> On Mon, Jun 20, 2022 at 10:26 AM Miquel Raynal
> <miquel.raynal@...tlin.com> wrote:
> >
> > Let's introduce the basics for defining PANs:
> > - structures defining a PAN
> > - helpers for PAN registration
> > - helpers discarding old PANs
> >  
> 
> I think the whole pan management can/should be stored in user space by
> a daemon running in background.

We need both, and currently:
- while the scan is happening, the kernel saves all the discovered PANs
- the kernel PAN list can be dumped (and also flushed) asynchronously by
  the userspace

IOW the userspace is responsible of keeping its own list of PANs in
sync with what the kernel discovers, so at any moment it can ask the
kernel what it has in memory, it can be done during a scan or after. It
can request a new scan to update the entries, or flush the kernel list.
The scan operation is always requested by the user anyway, it's not
something happening in the background.

> This can be a network manager as it
> listens to netlink events as "detect PAN xy" and stores it and offers
> it in their list to associate with it.

There are events produced, yes. But really, this is not something we
actually need. The user requests a scan over a given range, when the
scan is over it looks at the list and decides which PAN it
wants to associate with, and through which coordinator (95% of the
scenarii).

> We need somewhere to draw a line and I guess the line is "Is this
> information used e.g. as any lookup or something in the hot path", I
> don't see this currently...

Each PAN descriptor is like 20 bytes, so that's why I don't feel back
keeping them, I think it's easier to be able to serve the list of PANs
upon request rather than only forwarding events and not being able to
retrieve the list a second time (at least during the development).

Overall I feel like this part is still a little bit blurry because it
has currently no user, perhaps I should send the next series which
actually makes the current series useful.

Thanks,
Miquèl