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Date: Thu, 25 Apr 2024 12:33:28 +0200
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Subject: Re: [PATCH v5 2/3] VT: Add KDFONTINFO ioctl
To: Alexey Gladkov <legion@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Jiri Slaby <jirislaby@kernel.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
References: <cover.1712080158.git.legion@kernel.org>
 <cover.1713375378.git.legion@kernel.org>
 <bd2755e7b6ebe9b49e82d04d9908a176e0fe2f15.1713375378.git.legion@kernel.org>
 <9019dc74-35ad-43d7-8763-cea3da93e9c1@gmx.de> <ZiD50WZZv3OOad7L@example.org>
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From: Helge Deller <deller@gmx.de>
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On 4/18/24 12:45, Alexey Gladkov wrote:
> On Wed, Apr 17, 2024 at 09:31:53PM +0200, Helge Deller wrote:
>> On 4/17/24 19:37, 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 minimum and maximum font size values.
>>>
>>> Acked-by: Helge Deller <deller@gmx.de>
>>> Signed-off-by: Alexey Gladkov <legion@kernel.org>
>>> ---
>>>    drivers/tty/vt/vt.c       | 24 ++++++++++++++++++++++++
>>>    drivers/tty/vt/vt_ioctl.c | 13 +++++++++++++
>>>    include/linux/console.h   |  3 +++
>>>    include/linux/vt_kern.h   |  1 +
>>>    include/uapi/linux/kd.h   | 14 ++++++++++++++
>>>    5 files changed, 55 insertions(+)
>>>
>>> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
>>> index 9b5b98dfc8b4..e8db0e9ea674 100644
>>> --- a/drivers/tty/vt/vt.c
>>> +++ b/drivers/tty/vt/vt.c
>>> @@ -4851,6 +4851,30 @@ int con_font_op(struct vc_data *vc, struct cons=
ole_font_op *op)
>>>    	return -ENOSYS;
>>>    }
>>>
>>> +int con_font_info(struct vc_data *vc, struct console_font_info *info)
>>> +{
>>> +	int rc;
>>> +
>>> +	info->min_height =3D 0;
>>> +	info->max_height =3D max_font_height;
>>> +
>>> +	info->min_width =3D 0;
>>> +	info->max_width =3D max_font_width;
>>> +
>>> +	info->flags =3D KD_FONT_INFO_FLAG_LOW_SIZE | KD_FONT_INFO_FLAG_HIGH_=
SIZE;
>>> +
>>> +	console_lock();
>>> +	if (vc->vc_mode !=3D KD_TEXT)
>>> +		rc =3D -EINVAL;
>>> +	else if (vc->vc_sw->con_font_info)
>>> +		rc =3D vc->vc_sw->con_font_info(vc, info);
>>> +	else
>>> +		rc =3D -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 4b91072f3a4e..9a2f8081f650 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, uns=
igned int cmd,
>>>    		break;
>>>    	}
>>>
>>> +	case KDFONTINFO: {
>>> +		struct console_font_info fnt_info;
>>> +
>>> +		memset(&fnt_info, 0, sizeof(fnt_info));
>>> +
>>> +		ret =3D con_font_info(vc, &fnt_info);
>>> +		if (ret)
>>> +			return ret;
>>> +		if (copy_to_user(up, &fnt_info, sizeof(fnt_info)))
>>> +			return -EFAULT;
>>> +		break;
>>> +	}
>>> +
>>>    	default:
>>>    		return -ENOIOCTLCMD;
>>>    	}
>>> diff --git a/include/linux/console.h b/include/linux/console.h
>>> index 31a8f5b85f5d..4b798322aa01 100644
>>> --- a/include/linux/console.h
>>> +++ b/include/linux/console.h
>>> @@ -21,6 +21,7 @@
>>>    #include <linux/vesa.h>
>>>
>>>    struct vc_data;
>>> +struct console_font_info;
>>>    struct console_font_op;
>>>    struct console_font;
>>>    struct module;
>>> @@ -102,6 +103,8 @@ struct consw {
>>>    	bool	(*con_switch)(struct vc_data *vc);
>>>    	bool	(*con_blank)(struct vc_data *vc, enum vesa_blank_mode blank,
>>>    			     bool mode_switch);
>>> +	int	(*con_font_info)(struct vc_data *vc,
>>> +				 struct console_font_info *info);
>>>    	int	(*con_font_set)(struct vc_data *vc,
>>>    				const struct console_font *font,
>>>    				unsigned int vpitch, unsigned int flags);
>>> diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
>>> index d008c3d0a9bb..383b3a4f6113 100644
>>> --- a/include/linux/vt_kern.h
>>> +++ b/include/linux/vt_kern.h
>>> @@ -33,6 +33,7 @@ void do_blank_screen(int entering_gfx);
>>>    void do_unblank_screen(int leaving_gfx);
>>>    void poke_blanked_console(void);
>>>    int con_font_op(struct vc_data *vc, struct console_font_op *op);
>>> +int con_font_info(struct vc_data *vc, struct console_font_info *info)=
;
>>>    int con_set_cmap(unsigned char __user *cmap);
>>>    int con_get_cmap(unsigned char __user *cmap);
>>>    void scrollback(struct vc_data *vc);
>>> diff --git a/include/uapi/linux/kd.h b/include/uapi/linux/kd.h
>>> index 8ddb2219a84b..68b715ad4d5c 100644
>>> --- a/include/uapi/linux/kd.h
>>> +++ b/include/uapi/linux/kd.h
>>> @@ -185,6 +185,20 @@ struct console_font {
>>>
>>>    #define KD_FONT_FLAG_DONT_RECALC 	1	/* Don't recalculate hw charcel=
l size [compat] */
>>>
>>> +/* font information */
>>> +
>>> +#define KD_FONT_INFO_FLAG_LOW_SIZE	_BITUL(0) /* 256 */
>>> +#define KD_FONT_INFO_FLAG_HIGH_SIZE	_BITUL(1) /* 512 */
>>
>> Do we really need those bits?
>> You set a default min/max font size in con_font_info() above,
>> and all drivers can override those values.
>> So, there are always min/max sizes available.
>
> These bits are not about the minimum and maximum glyph size, but about t=
he
> number of glyphs in the font.
>
> Maybe this is an overkill, but sticon has this check:
>
> if ((w < 6) || (h < 6) || (w > 32) || (h > 32) || (vpitch !=3D 32)
>      || (op->charcount !=3D 256 && op->charcount !=3D 512))
>
> [ to be honest, I don=E2=80=99t know why this driver doesn=E2=80=99t acc=
ept a glyph of
> width 4 ]

I think there was no technical limitation when I added that.
It's just that the font would be so small...

> I thought it would be worth fixing the maximum number of requirements in
> the drivers since I started adding a new ioctl.

Ok.

Helge