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Date:   Mon, 30 Oct 2023 22:29:02 +0000
From:   Long Li <>
To:     Jakub Kicinski <>,
        "" <>
CC:     KY Srinivasan <>,
        Haiyang Zhang <>,
        Wei Liu <>, Dexuan Cui <>,
        "David S. Miller" <>,
        Eric Dumazet <>,
        Paolo Abeni <>,
        "" <>,
        "" <>,
        "" <>
Subject: RE: [Patch v2] hv_netvsc: Mark VF as slave before exposing it to

> Subject: Re: [Patch v2] hv_netvsc: Mark VF as slave before exposing it to user-
> mode
> On Fri, 27 Oct 2023 13:59:50 -0700 wrote:
> > When a VF is being exposed form the kernel, it should be marked as "slave"
> > 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 "slave"
> flag.
> >
> > This commit moves the code of setting the slave flag to the time
> > before VF is exposed to user-mode.
> 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-mode, 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)

> 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 original 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. 

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