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

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Message-ID: <Zha-X8QS_8L9eF0r@example.org>
Date: Wed, 10 Apr 2024 18:29:19 +0200
From: Alexey Gladkov <legion@...nel.org>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>, kbd@...ts.linux.dev,
	linux-api@...r.kernel.org, linux-fbdev@...r.kernel.org,
	linux-serial@...r.kernel.org, Helge Deller <deller@....de>
Subject: Re: [RESEND PATCH v3 1/2] VT: Add KDFONTINFO ioctl

On Wed, Apr 03, 2024 at 07:27:55AM +0200, Jiri Slaby wrote:
> 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).

struct console_font_info {
       __u32 min_width, min_height;    /* minimal font size */
       __u32 max_width, max_height;    /* maximum font size */
       __u32  flags;                   /* KD_FONT_INFO_FLAG_* */
       __u32 reserved[5];              /* This field is reserved forfuture use. Must be 0. */
};

So, struct should be like this ?

I wouldn't add the version to the flags. Maybe it would be better to add a
separate field with the version?

-- 
Rgrds, legion