linux-kernel - Re: [RFC PATCH 1/5] uapi/linux/if_tun.h: Added new ioctl for tun/tap.

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Message-ID: <CABcq3pH7HnH_-nCHcX7eet_ouqocQEptp6A9GCbs3=9guArhPA@mail.gmail.com>
Date:   Tue, 22 Feb 2022 15:28:21 +0200
From:   Andrew Melnichenko <andrew@...nix.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        Yuri Benditovich <yuri.benditovich@...nix.com>,
        Yan Vugenfirer <yan@...nix.com>
Subject: Re: [RFC PATCH 1/5] uapi/linux/if_tun.h: Added new ioctl for tun/tap.

Hi all,

On Wed, Feb 9, 2022 at 6:26 AM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 在 2022/1/25 下午4:46, Andrew Melnychenko 写道:
> > Added TUNGETSUPPORTEDOFFLOADS that should allow
> > to get bits of supported offloads.
>
>
> So we don't use dedicated ioctls in the past, instead, we just probing
> by checking the return value of TUNSETOFFLOADS.
>
> E.g qemu has the following codes:
>
> int tap_probe_has_ufo(int fd)
> {
>      unsigned offload;
>
>      offload = TUN_F_CSUM | TUN_F_UFO;
>
>      if (ioctl(fd, TUNSETOFFLOAD, offload) < 0)
>          return 0;
>
>      return 1;
> }
>
> Any reason we can't keep using that?
>
> Thanks
>

Well, even in this example. To check the ufo feature, we trying to set it.
What if we don't need to "enable" UFO and/or do not change its state?
I think it's a good idea to have the ability to get supported offloads
without changing device behavior.

>
> > Added 2 additional offlloads for USO(IPv4 & IPv6).
> > Separate offloads are required for Windows VM guests,
> > g.e. Windows may set USO rx only for IPv4.
> >
> > Signed-off-by: Andrew Melnychenko <andrew@...nix.com>
> > ---
> >   include/uapi/linux/if_tun.h | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
> > index 454ae31b93c7..07680fae6e18 100644
> > --- a/include/uapi/linux/if_tun.h
> > +++ b/include/uapi/linux/if_tun.h
> > @@ -61,6 +61,7 @@
> >   #define TUNSETFILTEREBPF _IOR('T', 225, int)
> >   #define TUNSETCARRIER _IOW('T', 226, int)
> >   #define TUNGETDEVNETNS _IO('T', 227)
> > +#define TUNGETSUPPORTEDOFFLOADS _IOR('T', 228, unsigned int)
> >
> >   /* TUNSETIFF ifr flags */
> >   #define IFF_TUN             0x0001
> > @@ -88,6 +89,8 @@
> >   #define TUN_F_TSO6  0x04    /* I can handle TSO for IPv6 packets */
> >   #define TUN_F_TSO_ECN       0x08    /* I can handle TSO with ECN bits. */
> >   #define TUN_F_UFO   0x10    /* I can handle UFO packets */
> > +#define TUN_F_USO4   0x20    /* I can handle USO for IPv4 packets */
> > +#define TUN_F_USO6   0x40    /* I can handle USO for IPv6 packets */
> >
> >   /* Protocol info prepended to the packets (when IFF_NO_PI is not set) */
> >   #define TUN_PKT_STRIP       0x0001
>