linux-kernel - Re: [PATCH v3] net/can/gs_usb: increase max interface to U8

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Message-ID: <63b1bd2d-fa5c-40f6-8e27-ada79dd196f2@coelacanthus.name>
Date: Tue, 30 Sep 2025 14:19:56 +0800
From: Celeste Liu <uwu@...lacanthus.name>
To: Vincent Mailhol <mailhol@...nel.org>
Cc: Maximilian Schneider <max@...neidersoft.net>,
 Henrik Brix Andersen <henrik@...xandersen.dk>,
 Wolfgang Grandegger <wg@...ndegger.com>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-can@...r.kernel.org,
 linux-kernel@...r.kernel.org, Runcheng Lu <runcheng.lu@...icro.com>,
 stable@...r.kernel.org, Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: [PATCH v3] net/can/gs_usb: increase max interface to U8_MAX

On 2025-09-30 13:44, Vincent Mailhol wrote:
> On 9/30/25 12:06 PM, Celeste Liu wrote:
>> This issue was found by Runcheng Lu when develop HSCanT USB to CAN FD
>> converter[1]. The original developers may have only 3 intefaces device to
>                                                         ^^^^^^^^^
> interfaces (missing "r")

Fixed in v4. Redundant typeof() was removed as well.

> 
>> test so they write 3 here and wait for future change.
>>
>> During the HSCanT development, we actually used 4 interfaces, so the
>> limitation of 3 is not enough now. But just increase one is not
>> future-proofed. Since the channel type in gs_host_frame is u8, just
>> increase interface number limit to max size of u8 safely.
>>
>> [1]: https://github.com/cherry-embedded/HSCanT-hardware
>>
>> Fixes: d08e973a77d1 ("can: gs_usb: Added support for the GS_USB CAN devices")
>> Reported-by: Runcheng Lu <runcheng.lu@...icro.com>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Celeste Liu <uwu@...lacanthus.name>
> 
> Reviewed-by: Vincent Mailhol <mailhol@...nel.org>
> 
> The patch is good as-is. However, speaking of the interface numbers, there is
> another issue in this gs_usb driver: net_device->dev_port is not populated, and
> according to the documentation, this is a bug.
> 
> 
> See the description here:
> 
> 
> 
>   https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-class-net
> 
> 
> 
>   What:		/sys/class/net/<iface>/dev_port
> 
>   Date:		February 2014
> 
>   KernelVersion:	3.15
> 
>   Contact:	netdev@...r.kernel.org
> 
>   Description:
> 
>   		Indicates the port number of this network device, formatted
> 
>   		as a decimal value. Some NICs have multiple independent ports
> 
>   		on the same PCI bus, device and function. This attribute allows
> 
>   		userspace to distinguish the respective interfaces.
> 
> 
> 
>   		Note: some device drivers started to use 'dev_id' for this
> 
>   		purpose since long before 3.15 and have not adopted the new
> 
>   		attribute ever since. To query the port number, some tools look
> 
>   		exclusively at 'dev_port', while others only consult 'dev_id'.
> 
>   		If a network device has multiple client adapter ports as
> 
>   		described in the previous paragraph and does not set this
> 
>   		attribute to its port number, it's a kernel bug.
> 
> 
> 
> Would you mind sending a separate patch (with a Fixes: tag) to resolve this?

Ok. I will send a patch for it later.

> 
> 
> Yours sincerely,
> Vincent Mailhol
>