Re: [Qemu-devel] [PATCH 0/3] Attempting to run Microport UNIX (ca 1987)

[Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>]

On Sat, Jul 28, 2012 at 08:33:54AM +0200, Markus Armbruster wrote:
> Matthew Ogilvie <mmogilvi_qemu@miniinfo.net> writes:
[...]
> >   1. It doesn't seem to recognize the hard drive geometry, even
> >      if I use "-hdachs" and keep it carefully inside ancient
> >      limitations.  Note that at the time, hard drives did not support
> >      self-identification commands for the geometry; you had to
> >      configure it in BIOS.   I also have some old notes from when my
> >      dad was asking Microport about compatibility; apparently
> >      they wanted to know the specific BIOS version in order to
> >      decide about compatibility.  Maybe UNIX is bypassing later
> >      standards for looking up geometry, and trying to get it in
> >      some non-standard way (straight from CMOS or something?)
> 
> Please run QEMU with -trace events=trace-events, where trace-events is a
> file containing the line "hd_geometry_*".  Post results, along with your
> full command line.
> 
> [...]

Thanks for the suggestion.  I've narrowed down a couple of problems
based on it:

First, the -hdachs command line option is silently ignored depending
on its relative order compared to other command line options.  I've
attached a patch below.

----

Second, this UNIX kernel and/or bootloader always seems to think
it has 17 sectors per track, no matter what I tell qemu (using a blank
image; no partition table).  But UNIX does recognize the number
of cylinders and heads correctly, and I've verified that
the number of sectors per track is also correct in the fixed disk
parameter table, by using the monitor's "x" (examine) command. 

Potentially guess_chs_for_size() could be enhanced to return 17
for small drive images when appropriate, to be consistent with most
legacy drives having 17.  Or maybe there is some more
obscure way to get UNIX to recognize non-17 sectors.
Or either document a third party way to put a basic partition table
on a new image, or add that ability to qemu-img, so that code
like that in guess_disk_lchs() or similar code that might exist
in some operating systems would have something to work with.
I also found a 1988 posting that suggests some leads for
further investigation:
http://www.megalextoria.com/usenet-archive/news076f1/b96/comp/unix/microport/00000798.html

But I'm not really inclined to worry much more about this
right now, because I have a usable workaround: Always define
my disk image size to be consistent with 17 sectors per
track, and tell qemu to use 17.

----

(Now if I can just figure out what's up with the sporadic panic
in UNIX's interrupt handlers...)

----

From: Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>
Date: Sat, 28 Jul 2012 17:01:14 -0600
Subject: [PATCH] vl.c: fix -hdachs/-hda argument order parsing issues

Without this patch, the -hdachs argument had to occur either
BEFORE the corresponding "-hda" option, or AFTER the plain
disk image name (if neither -hda nor -drive is used).  Otherwise
it would effectively be ignored.

Option -hdachs still has no effect on -drive, but that seems
reasonable.

Signed-off-by: Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>
---
 vl.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/vl.c b/vl.c
index c18bb80..e0611eb 100644
--- a/vl.c
+++ b/vl.c
@@ -2374,7 +2374,18 @@ int main(int argc, char **argv, char **envp)
         if (optind >= argc)
             break;
         if (argv[optind][0] != '-') {
-	    hda_opts = drive_add(IF_DEFAULT, 0, argv[optind++], HD_OPTS);
+            char buf[256];
+            if (cyls == 0)
+                snprintf(buf, sizeof(buf), "%s", HD_OPTS);
+            else
+                snprintf(buf, sizeof(buf),
+                         "%s,cyls=%d,heads=%d,secs=%d%s",
+                         HD_OPTS , cyls, heads, secs,
+                         translation == BIOS_ATA_TRANSLATION_LBA ?
+                         ",trans=lba" :
+                         translation == BIOS_ATA_TRANSLATION_NONE ?
+                         ",trans=none" : "");
+            hda_opts = drive_add(IF_DEFAULT, 0, argv[optind++], buf);
         } else {
             const QEMUOption *popt;
 
@@ -2404,7 +2415,7 @@ int main(int argc, char **argv, char **envp)
                                  ",trans=lba" :
                                  translation == BIOS_ATA_TRANSLATION_NONE ?
                                  ",trans=none" : "");
-                    drive_add(IF_DEFAULT, 0, optarg, buf);
+                    hda_opts = drive_add(IF_DEFAULT, 0, optarg, buf);
                     break;
                 }
             case QEMU_OPTION_hdb:
-- 
1.7.10.2.484.gcd07cc5