netdev - Re: [PATCH wpan-next v3 09/11] net: mac802154: Introduce a synchronous API for MLME commands

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Message-ID: <CAB_54W6D-tr_c7dMbcLUO0VFfFz7vDgjjW+nRE4pWg78xqdbYg@mail.gmail.com>
Date:   Wed, 18 May 2022 08:12:48 -0400
From:   Alexander Aring <alex.aring@...il.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Alexander Aring <aahringo@...hat.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        linux-wpan - ML <linux-wpan@...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>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH wpan-next v3 09/11] net: mac802154: Introduce a
 synchronous API for MLME commands

Hi,

On Wed, May 18, 2022 at 7:59 AM Alexander Aring <alex.aring@...il.com> wrote:
>
> Hi,
>
> On Wed, May 18, 2022 at 4:44 AM Miquel Raynal <miquel.raynal@...tlin.com> wrote:
> >
> > Hi Alexander,
> >
> > aahringo@...hat.com wrote on Tue, 17 May 2022 20:41:41 -0400:
> >
> > > Hi,
> > >
> > > On Tue, May 17, 2022 at 12:35 PM Miquel Raynal
> > > <miquel.raynal@...tlin.com> wrote:
> > > >
> > > > This is the slow path, we need to wait for each command to be processed
> > > > before continuing so let's introduce an helper which does the
> > > > transmission and blocks until it gets notified of its asynchronous
> > > > completion. This helper is going to be used when introducing scan
> > > > support.
> > > >
> > > > Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> > > > ---
> > > >  net/mac802154/ieee802154_i.h |  1 +
> > > >  net/mac802154/tx.c           | 46 ++++++++++++++++++++++++++++++++++++
> > > >  2 files changed, 47 insertions(+)
> > > >
> > > > diff --git a/net/mac802154/ieee802154_i.h b/net/mac802154/ieee802154_i.h
> > > > index a057827fc48a..b42c6ac789f5 100644
> > > > --- a/net/mac802154/ieee802154_i.h
> > > > +++ b/net/mac802154/ieee802154_i.h
> > > > @@ -125,6 +125,7 @@ extern struct ieee802154_mlme_ops mac802154_mlme_wpan;
> > > >  void ieee802154_rx(struct ieee802154_local *local, struct sk_buff *skb);
> > > >  void ieee802154_xmit_sync_worker(struct work_struct *work);
> > > >  int ieee802154_sync_and_hold_queue(struct ieee802154_local *local);
> > > > +int ieee802154_mlme_tx_one(struct ieee802154_local *local, struct sk_buff *skb);
> > > >  netdev_tx_t
> > > >  ieee802154_monitor_start_xmit(struct sk_buff *skb, struct net_device *dev);
> > > >  netdev_tx_t
> > > > diff --git a/net/mac802154/tx.c b/net/mac802154/tx.c
> > > > index 38f74b8b6740..6cc4e5c7ba94 100644
> > > > --- a/net/mac802154/tx.c
> > > > +++ b/net/mac802154/tx.c
> > > > @@ -128,6 +128,52 @@ int ieee802154_sync_and_hold_queue(struct ieee802154_local *local)
> > > >         return ieee802154_sync_queue(local);
> > > >  }
> > > >
> > > > +static int ieee802154_mlme_op_pre(struct ieee802154_local *local)
> > > > +{
> > > > +       return ieee802154_sync_and_hold_queue(local);
> > > > +}
> > > > +
> > > > +static int ieee802154_mlme_tx(struct ieee802154_local *local, struct sk_buff *skb)
> > > > +{
> > > > +       int ret;
> > > > +
> > > > +       /* Avoid possible calls to ->ndo_stop() when we asynchronously perform
> > > > +        * MLME transmissions.
> > > > +        */
> > > > +       rtnl_lock();
> > > > +
> > > > +       /* Ensure the device was not stopped, otherwise error out */
> > > > +       if (!local->open_count)
> > > > +               return -EBUSY;
> > > > +
> > >
> > > No -EBUSY here, use ?-ENETDOWN?.
> >
> > Isn't it strange to return "Network is down" while we try to stop the
> > device but fail to do so because, actually, it is still being used?
> >
>
> you are right. Maybe -EPERM, in a sense of whether the netdev state
> allows it or not.

or maybe not, if this is the error the user gets by running iwpan. The
problem I have with -EBUSY is that it indicates some resource is being
used and will be solved at some time. Especially in a transmit
function e.g. framebuffer.

- Alex