hw/block/hd-geometry: Do not override specified bios-chs-trans

For small disk images (<4 GiB), QEMU and SeaBIOS default to the
LARGE/ECHS disk translation method, but it is not uncommon for other
BIOS software to use LBA in these cases as well.  Some operating
system boot loaders (e.g., NT 4) do not handle LARGE translations
outside of fixed configurations.  See, e.g., Q154052:

"When starting an x86 based computer, Ntdetect.com retrieves and
stores Interrupt 13 information. . . If the disk controller is using a
32 sector/64 head translation scheme, this boundary will be 1 GB. If
the controller uses 63 sector/255 head translation [AUTHOR: i.e.,
LBA], the limit will be 4 GB."

To accommodate these situations, hd_geometry_guess() now follows the
disk translation specified by the user even when the ATA disk geometry
is guessed.

hd_geometry_guess():
* Only set the disk translation when translation is AUTO.
* Show the soon-to-be active translation (*ptrans) in the trace rather
  than what was guessed.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/56
Buglink: https://bugs.launchpad.net/qemu/+bug/1745312

Signed-off-by: Lev Kujawski <lkujaw@member.fsf.org>
Message-Id: <20220707204045.999544-1-lkujaw@member.fsf.org>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/hw/block/hd-geometry.c b/hw/block/hd-geometry.c
index 1120943..dae13ab 100644
--- a/hw/block/hd-geometry.c
+++ b/hw/block/hd-geometry.c
@@ -150,7 +150,12 @@ void hd_geometry_guess(BlockBackend *blk,
         translation = BIOS_ATA_TRANSLATION_NONE;
     }
     if (ptrans) {
-        *ptrans = translation;
+        if (*ptrans == BIOS_ATA_TRANSLATION_AUTO) {
+            *ptrans = translation;
+        } else {
+            /* Defer to the translation specified by the user.  */
+            translation = *ptrans;
+        }
     }
     trace_hd_geometry_guess(blk, *pcyls, *pheads, *psecs, translation);
 }