Re: [RESEND PATCH v3 1/2] VT: Add KDFONTINFO ioctl

From: Jiri Slaby <jirislaby@kernel.org>
To: Alexey Gladkov <legion@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kbd@lists.linux.dev, linux-api@vger.kernel.org,
	linux-fbdev@vger.kernel.org, linux-serial@vger.kernel.org,
	Helge Deller <deller@gmx.de>
Subject: Re: [RESEND PATCH v3 1/2] VT: Add KDFONTINFO ioctl
Date: Wed, 3 Apr 2024 07:27:55 +0200	[thread overview]
Message-ID: <6bb4f4fb-573c-4f63-967c-2cb08514fc91@kernel.org> (raw)
In-Reply-To: <ZgwF72yHH_0-A4FW@example.org>

On 02. 04. 24, 15:19, Alexey Gladkov wrote:
>>> --- a/include/uapi/linux/kd.h
>>> +++ b/include/uapi/linux/kd.h
...
>>> +struct console_font_info {
>>> +	unsigned int min_width, min_height;	/* minimal font size */
>>> +	unsigned int max_width, max_height;	/* maximum font size */
>>> +	unsigned int flags;			/* KD_FONT_INFO_FLAG_* */
>>
>> This does not look like a well-defined™ and extendable uapi structure.
>> While it won't change anything here, still use fixed-length __u32.
>>
>> And you should perhaps add some reserved fields. Do not repeat the same
>> mistakes as your predecessors with the current kd uapi.
> 
> I thought about it, but I thought it would be overengineering.

It would not. UAPI structs are set in stone once released.

And in this case, it's likely you would want to know more info about 
fonts in the future.

> Can you suggest how best to do this?

Given you have flags in there already (to state that the structure 
contains more), just add an array of u32 reserved[] space. 3 or 5, I 
would say (to align the struct to 64bit).

thanks,
-- 
js
suse labs