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Message-ID: <2024041830-feisty-gristle-5fd0@gregkh>
Date: Thu, 18 Apr 2024 08:18:33 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Alexey Gladkov <legion@...nel.org>
Cc: Jiri Slaby <jirislaby@...nel.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: [PATCH v5 2/3] VT: Add KDFONTINFO ioctl
On Wed, Apr 17, 2024 at 07:37:36PM +0200, 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.
Is there any userspace code that uses this yet that we can point to
here?
I know tty ioctls are woefully undocumented, but could there be some
documentation here?
>
> 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 | 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 console_font_op *op)
> return -ENOSYS;
> }
>
> +int con_font_info(struct vc_data *vc, struct console_font_info *info)
> +{
> + int rc;
> +
> + 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 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, unsigned int cmd,
> break;
> }
>
> + case KDFONTINFO: {
> + struct console_font_info fnt_info;
> +
> + memset(&fnt_info, 0, sizeof(fnt_info));
> +
> + ret = con_font_info(vc, &fnt_info);
Shouldn't con_font_info() memset it first? No need to do it in the
caller.
> + 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);
To make the names more obvious, how about:
con_font_info_get()?
> 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 charcell size [compat] */
>
> +/* font information */
> +
> +#define KD_FONT_INFO_FLAG_LOW_SIZE _BITUL(0) /* 256 */
> +#define KD_FONT_INFO_FLAG_HIGH_SIZE _BITUL(1) /* 512 */
I don't understand why bit 0 and bit 1 have those comments after them.
That's confusing (i.e. bit 0 is NOT 256...)
> +
> +struct console_font_info {
> + __u32 flags; /* KD_FONT_INFO_FLAG_* */
Why are there flags if you are only setting these 2 values? What are
the flags for?
If this is going to be a "multiplexed" type of structure, then make it a
union? Or maybe we are totally over thinking this whole thing.
All you want is the min/max font size of the console, right? So perhaps
the whole structure is just:
> + __u32 min_width, min_height; /* minimal font size */
> + __u32 max_width, max_height; /* maximum font size */
Those 4 variables? Why have anything else here at all? For any new
thing you wish to discover, have it be a new ioctl?
> + __u32 reserved[5]; /* This field is reserved for future use. Must be 0. */
I understand the "must be 0" but this is a read-only structure, so
saying "it will be set to 0" might be better?" Or something like that?
> +};
> +
> +#define KDFONTINFO _IOR(KD_IOCTL_BASE, 0x73, struct console_font_info)
As mentioned above how about KDFONTINFOGET?
thanks,
greg k-h
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