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

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Date:   Wed, 9 Feb 2022 12:25:54 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Andrew Melnychenko <andrew@...nix.com>, davem@...emloft.net,
        kuba@...nel.org, mst@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Cc:     yuri.benditovich@...nix.com, yan@...nix.com
Subject: Re: [RFC PATCH 1/5] uapi/linux/if_tun.h: Added new ioctl for tun/tap.


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


> 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