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From:   Long Li <longli@microsoft.com>
To:     Jakub Kicinski <kuba@kernel.org>,
        "longli@linuxonhyperv.com" <longli@linuxonhyperv.com>
CC:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
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        Paolo Abeni <pabeni@redhat.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [Patch v2] hv_netvsc: Mark VF as slave before exposing it to
 user-mode
Thread-Topic: [Patch v2] hv_netvsc: Mark VF as slave before exposing it to
 user-mode
Thread-Index: AQHaCRiSNRG1yvvd4UWGUKbgbSduNLBi3RQAgAAJr+A=
Date:   Mon, 30 Oct 2023 22:29:02 +0000
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 <20231030142542.6640190b@kernel.org>
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> Subject: Re: [Patch v2] hv_netvsc: Mark VF as slave before exposing it to=
 user-
> mode
>=20
> On Fri, 27 Oct 2023 13:59:50 -0700 longli@linuxonhyperv.com wrote:
> > When a VF is being exposed form the kernel, it should be marked as "sla=
ve"
> > before exposing to the user-mode. The VF is not usable without netvsc
> > running as master. The user-mode should never see a VF without the "sla=
ve"
> flag.
> >
> > This commit moves the code of setting the slave flag to the time
> > before VF is exposed to user-mode.
>=20
> Can you give a real example in the commit message of a flow in user space
> which would get confused by seeing the VF netdev without IFF_SLAVE?

A user-mode program may see the VF netdev show up without SLAVE flag before=
 seeing the NETVSC netdev. It may try to configure the VF before it will be=
 bonded to a NETVSC.

With the IFF_SLAVE correctly set at the time of VF showing up to the user-m=
ode, it can rely on this flag to decide if this device should be ignored. (=
without implementing some timeout logic to detect a potential NETVSC device=
 that may show up later)

>=20
> You're only moving setting IFF_SLAVE but not linking the master, is there=
 no
> code which would assume that if SLAVE is set there is a master?

The same (taking IFF_SLAVE without linking to master) is done in the origin=
al code before VF is joined, but it was for another purpose. I think there =
is a gap between when the VF is acted upon by other parts of the system and=
 when it's bonded.=20