linux-kernel - Re: [PATCH] vt_ioctl: make VT_RESIZEX behave like VT

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Message-ID: <CAHk-=wgF8e5i+9eeGu=CgWAagTPv-9UbkG7B6bR5jDe6kkkFZQ@mail.gmail.com>
Date:   Sun, 11 Apr 2021 15:15:35 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Martin Hostettler <textshell@...uujin.de>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Jiri Slaby <jirislaby@...nel.org>,
        Peilin Ye <yepeilin.cs@...il.com>,
        syzbot <syzbot+b308f5fd049fbbc6e74f@...kaller.appspotmail.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Helge Deller <deller@....de>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        George Kennedy <george.kennedy@...cle.com>
Subject: Re: [PATCH] vt_ioctl: make VT_RESIZEX behave like VT_RESIZE

On Sun, Apr 11, 2021 at 2:43 PM Maciej W. Rozycki <macro@...am.me.uk> wrote:
>
>  So it does trigger with vgacon and my old server, which I have started
> experimenting with and for a start I have switched to a new kernel for an
> unrelated purpose (now that I have relieved it from all its usual tasks
> except for the last remaining one for which I haven't got the required
> user software ported to the new system yet):
>
> "struct vt_consize"->v_vlin is ignored. Please report if you need this.
> "struct vt_consize"->v_clin is ignored. Please report if you need this.

Note that it's entirely possible that things continue to work well
despite this warning. It's unclear to me from your email if you
actually see any difference (and apparently you're not able to see it
right now due to not being close to the machine).

The fact that v_vlin/v_clin are ignored doesn't necessarily mean that
they are different from what they were before, so the warning may be a
non-issue.

> It continues using svgatextmode with its glass (CRT) VT to set my usual
> 80x37 text mode (720x576 pixel resolution) by manipulating the VGA clock
> chip and the CRT controller appropriately for a nice refresh rate of 85Hz:
>
> Chipset = `TVGA8900', Textmode clock = 44.90 MHz, 80x37 chars, CharCell = 9x16. Refresh = 52.51kHz/84.7Hz.

That doesn't seem necessarily wrong to me.

>  So what's the supposed impact of this change that prompted the inclusion
> of the messages?

There _may_ be no impact at all apart from the messages.

The code _used_ to set the scan lines (v_vlin) and font height
(v_clin) from those numbers if they were non-zero, and now it just
ignores them and warns instead.

The code now just sets the font height from the actual font size when
the font is set. Which is honestly the only thing that ever made
sense. Trying to set it with v_clin is ignored, but it's entirely
possible - maybe even likely - that your user of VT_RESIZEX sets it to
the same values it already has.

Exactly because setting a font line number to anything else than the
font size isn't exactly sensible.

But if your screen looks different than it used to, that is obviously
interesting and says something actually changed (outside of the
message itself).

           Linus