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From:   Ganesh Babu <ganesh.babu@ekinops.com>
To:     Jakub Kicinski <kuba@kernel.org>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ganesh Babu <ganesh.babu@ekinops.com>
Subject: Re: [PATCH] net: mroute6.h: change type of mif6c_pifi to __u32
Thread-Topic: [PATCH] net: mroute6.h: change type of mif6c_pifi to __u32
Thread-Index: AQHZYUP13XlrMpW17Ue8ZSjM0wOOK68RBfoAgCx+iec=
Date:   Tue, 2 May 2023 08:07:10 +0000
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Thank you for your response. Regarding the proposed change to=0A=
the mif6ctl structure in mroute6.h, I would like to clarify,=0A=
that changing the datatype of mif6c_pifi from __u16 to __u32=0A=
will not change the offset of the structure members, which=0A=
means that the size of the structure remains the same and=0A=
the ABI remains compatible. Furthermore, ifindex is treated=0A=
as an integer in all the subsystems of the kernel and not=0A=
as a 16-bit value. Therefore, changing the datatype of=0A=
mif6c_pifi from __u16 to __u32 is a natural and expected=0A=
change that aligns with the existing practice in the kernel.=0A=
I understand that the mif6ctl structure is part of the uAPI=0A=
and changing its geometry is not allowed. However, in this=0A=
case, we are not changing the geometry of the structure,=0A=
as the size of the structure remains the same and the offset=0A=
of the structure members will not change. Thus, the proposed=0A=
change will not affect the ABI or the user API. Instead, it=0A=
will allow the kernel to handle 32-bit ifindex values without=0A=
any issues, which is essential for the smooth functioning of=0A=
the PIM6 protocol. I hope this explanation clarifies any=0A=
concerns you may have had. Let me know if you have any further=0A=
questions or need any more details.=0A=
=0A=
Signed-off-by: Ganesh Babu <ganesh.babu@ekinops.com>=0A=
=0A=
From: Jakub Kicinski <kuba@kernel.org>=0A=
Sent: 29 March 2023 07:44=0A=
To: Ganesh Babu <ganesh.babu@ekinops.com>=0A=
Cc: netdev@vger.kernel.org <netdev@vger.kernel.org>; linux-kernel@vger.kern=
el.org <linux-kernel@vger.kernel.org>=0A=
Subject: Re: [PATCH] net: mroute6.h: change type of mif6c_pifi to __u32 =0A=
=A0=0A=
On Tue, 28 Mar 2023 07:13:03 +0000 Ganesh Babu wrote:=0A=
> From a91f11fe060729d0009a3271e3a92cead88e2656 Mon Sep 17 00:00:00 2001=0A=
> From: "Ganesh Babu" <ganesh.babu@ekinops.com>=0A=
> Date: Wed, 15 Mar 2023 15:01:39 +0530=0A=
> Subject: [PATCH] net: mroute6.h: change type of mif6c_pifi to __u32=0A=
> =0A=
> Increase mif6c_pifi field in mif6ctl struct=0A=
> from 16 to 32 bits to support 32-bit ifindices.=0A=
> The field stores the physical interface (ifindex) for a multicast group.=
=0A=
> Passing a 32-bit ifindex via MRT6_ADD_MIF socket option=0A=
> from user space can cause unpredictable behavior in PIM6.=0A=
> Changing mif6c_pifi to __u32 allows kernel to handle=0A=
> 32-bit ifindex values without issues.=0A=
=0A=
The patch is not formatted correctly.=0A=
Maybe try git send-email next time?=0A=
=0A=
> diff --git a/include/uapi/linux/mroute6.h b/include/uapi/linux/mroute6.h=
=0A=
> index 1d90c21a6251..90e6e771beab 100644=0A=
> --- a/include/uapi/linux/mroute6.h=0A=
> +++ b/include/uapi/linux/mroute6.h=0A=
> @@ -75,7 +75,7 @@ struct mif6ctl {=0A=
> =A0 =A0 =A0 =A0 mifi_t =A0mif6c_mifi; =A0 =A0 =A0 =A0 =A0 =A0 /* Index of=
 MIF */=0A=
> =A0 =A0 =A0 =A0 unsigned char mif6c_flags; =A0 =A0 =A0/* MIFF_ flags */=
=0A=
> =A0 =A0 =A0 =A0 unsigned char vifc_threshold; =A0 /* ttl limit */=0A=
> - =A0 =A0 =A0 __u16 =A0 =A0mif6c_pifi; =A0 =A0 =A0 =A0 =A0 =A0/* the inde=
x of the physical IF */=0A=
> + =A0 =A0 =A0 __u32 =A0 =A0mif6c_pifi; =A0 =A0 =A0 =A0 =A0 =A0/* the inde=
x of the physical IF */=0A=
=0A=
Unfortunately we can't do this. The structure is part of uAPI,=0A=
we can't change it's geometry. The kernel must maintain binary=0A=
backward compatibility. =0A=
=0A=
> =A0 =A0 =A0 =A0 unsigned int vifc_rate_limit; =A0 /* Rate limiter values =
(NI) */=0A=
> =A0};=0A=
> =0A=
> --=0A=
> 2.11.0=0A=
> =0A=
> Signed-off-by: Ganesh Babu <ganesh.babu@ekinops.com>=0A=
> ---=0A=