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

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Message-ID: <74ca50e0-61b1-4d4c-85dd-a5d920548c04@kernel.org>
Date: Tue, 2 Apr 2024 13:02:20 +0200
From: Jiri Slaby <jirislaby@...nel.org>
To: Alexey Gladkov <legion@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: 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

Hi,

On 02. 04. 24, 12:32, Alexey Gladkov wrote:
> Each driver has its own restrictions on font size. There is currently no
> way to understand what the requirements are. The new ioctl allows
> userspace to get the minmum and maximum font size values.

minimum

> Acked-by: Helge Deller <deller@....de>
> Signed-off-by: Alexey Gladkov <legion@...nel.org>
> ---
>   drivers/tty/vt/vt.c       | 24 ++++++++++++++++++++++++
>   drivers/tty/vt/vt_ioctl.c | 13 +++++++++++++
>   include/linux/console.h   |  2 ++
>   include/linux/vt_kern.h   |  1 +
>   include/uapi/linux/kd.h   | 13 ++++++++++++-
>   5 files changed, 52 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index 156efda7c80d..8c2a3d98b5ec 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -4680,6 +4680,30 @@ int con_font_op(struct vc_data *vc, struct console_font_op *op)
>   	return -ENOSYS;
>   }
>   
> +int con_font_info(struct vc_data *vc, struct console_font_info *info)
> +{
> +	int rc = -EINVAL;

This initialization appears to be unneeded.

> +
> +	info->min_height = 0;
> +	info->max_height = max_font_height;
> +
> +	info->min_width = 0;
> +	info->max_width = max_font_width;
> +
> +	info->flags = KD_FONT_INFO_FLAG_LOW_SIZE | KD_FONT_INFO_FLAG_HIGH_SIZE;
> +
> +	console_lock();
> +	if (vc->vc_mode != KD_TEXT)
> +		rc = -EINVAL;
> +	else if (vc->vc_sw->con_font_info)
> +		rc = vc->vc_sw->con_font_info(vc, info);
> +	else
> +		rc = -ENOSYS;
> +	console_unlock();
> +
> +	return rc;
> +}
> +
>   /*
>    *	Interface exported to selection and vcs.
>    */
> diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
> index 8c685b501404..b3b4e4b69366 100644
> --- a/drivers/tty/vt/vt_ioctl.c
> +++ b/drivers/tty/vt/vt_ioctl.c
> @@ -479,6 +479,19 @@ static int vt_k_ioctl(struct tty_struct *tty, unsigned int cmd,
>   		break;
>   	}
>   
> +	case KDFONTINFO: {
> +		struct console_font_info fnt_info;
> +
> +		if (copy_from_user(&fnt_info, up, sizeof(fnt_info)))
> +			return -EFAULT;

Who uses the copied values?

> +		ret = con_font_info(vc, &fnt_info);
> +		if (ret)
> +			return ret;
> +		if (copy_to_user(up, &fnt_info, sizeof(fnt_info)))

We should do the preferred sizeof(*up) here...

> +			return -EFAULT;
> +		break;
> +	}
> +
>   	default:
>   		return -ENOIOCTLCMD;
>   	}
..
> --- a/include/uapi/linux/kd.h
> +++ b/include/uapi/linux/kd.h
> @@ -183,8 +183,19 @@ struct console_font {
>   
>   #define KD_FONT_FLAG_DONT_RECALC 	1	/* Don't recalculate hw charcell size [compat] */
>   
> +#define KDFONTINFO	0x4B73	/* font information */

Why not properly define the number using IOC() et al.? K (that 0x4b) is 
even reserved for kd.h.

> +#define KD_FONT_INFO_FLAG_LOW_SIZE	(1U << 0) /* 256 */
> +#define KD_FONT_INFO_FLAG_HIGH_SIZE	(1U << 1) /* 512 */

_BITUL()

> +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.

> +};

thanks,
-- 
js
suse labs