Re: [PATCH] vt_ioctl: make VT_RESIZEX behave like VT_RESIZE

On Mon, 12 Apr 2021, Daniel Vetter wrote:

...

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).

Original search didn't turn up any users of VT_RESIZEX, this is the first. And looking at the source code I think we could outright remove support for VT_RESIZEX (but make it silent) and everything should keep working:

    /*
     * ALWAYS do a VT_RESIZE, even if we already did a VT_RESIZEX

on a 1.3.3 or higher kernel, * until those kernel programmers make this unambiguous */

   if (do_VT_RESIZE(curr_textmode->cols, curr_textmode->rows,

resize1x1)) sresize=TRUE;

   if (check_kernel_version(1,3,3, "VT_RESIZEX"))
     {
       /*
        * VDisplay must de divided by 2 for DoubleScan modes,
        * or VT_RESIZEX will fail -- until someone fixes the kernel
        * so it understands about doublescan modes.
        */
       if (do_VT_RESIZEX(curr_textmode->cols,
                         curr_textmode->rows,
                         curr_textmode->VDisplay /

(MOFLG_ISSET(curr_textmode, ATTR_DOUBLESCAN) ? 2 : 1), curr_textmode->FontHeight, curr_textmode->HDisplay/8*curr_textmode->FontWidth, curr_textmode->FontWidth, resize1x1)) sresize=TRUE; }

The functions are just straightforward wrappers. There's also no cvs repo, changelog or old releases before 2000 that would shed some light on why this code even exists.

I did some archaeology then, using a local copy of the linux-mips.org Linux tree that has historic information imported from the old oss.sgi.com MIPS/Linux CVS repo. According to that the ioctl was added with or shortly before 2.1.14:

commit beb116954b9b7f3bb56412b2494b562f02b864b1 Author: Ralf Baechle ralf@linux-mips.org Date: Tue Jan 7 02:33:00 1997 +0000

Import of Linux/MIPS 2.1.14

and, importantly, it was used to set some parameters:

if ( vlin ) video_scan_lines = vlin; if ( clin ) video_font_height = clin;

used by `con_adjust_height' in drivers/char/vga.c: `video_scan_lines' to set the vertical display limit (so that it is a whole multiple of the new font height) and `video_font_height' to set the cursor scan lines in the CRTC. The function was used by the PIO_FONTX and PIO_FONTRESET VT ioctls at that point.

That code was moved to `vgacon_adjust_height' in drivers/video/vgacon.c and then drivers/video/console/vgacon.c. The code is still there, serving the KDFONTOP ioctl.

With:

commit 9736a3546de7b6a2b16ad93539e4b3ac72b385bb Author: Ralf Baechle ralf@linux-mips.org Date: Thu Jun 5 10:06:35 2003 +0000

Merge with Linux 2.5.66.

the parameters were moved into `struct vc_data':

if (vlin) - video_scan_lines = vlin; + vc->vc_scan_lines = vlin; if (clin) - video_font_height = clin; + vc->vc_font.height = clin;

and this piece of code to set them only removed with the change discussed here.

So without even looking at the VT, which I'll surely get to eventually, I conclude this change regresses font resizing (KD_FONT_OP_SET) once a new resolution has been set with svgatextmode. I think this change needs to be reverted, especially as the problematic PIO_FONT ioctl referred has been since removed with commit ff2047fb755d ("vt: drop old FONT ioctls").

Maciej