v1:

Non-standard logical geometries break under QEMU.

A virtual disk which contains an operating system which depends on
logical geometries (consistent values being reported from BIOS INT13
AH=08) will most likely break under QEMU/SeaBIOS if it has non-standard
logical geometries - for example 56 SPT (sectors per track).
No matter what QEMU will guess - SeaBIOS, for large enough disks - will
use LBA translation, which will report 63 SPT instead.

In addition we can not enforce SeaBIOS to rely on phyiscal geometries at
all. A virtio-blk-pci virtual disk with 255 phyiscal heads can not
report more than 16 physical heads when moved to an IDE controller, the
ATA spec allows a maximum of 16 heads - this is an artifact of
virtualization.

By supplying the logical geometies directly we are able to support such
"exotic" disks.

We will use fw_cfg to do just that.

v2:

Rename bootdevices fw_cfg key to bios-geoemtry

v3:

Change fw_cfg interface from mixed binary/textual to textual only
Squash commit "config: Add toggle for bootdevice information"

v4:

* Rename TRANSLATION_MACHINE to TRANSLATION_HOST
* Rename "overriden" translation name to "host-supplied"
* Rename overriden_lchs_supplied() to host_lchs_supplied()
* Move sectors and heads check to host_lchs_supplied()
* Reuse duplicate code in boot.c

Sam Eiderman (5):
  geometry: Read LCHS from fw_cfg
  boot: Reorder functions in boot.c
  boot: Build ata and scsi paths in function
  geometry: Add boot_lchs_find_*() utility functions
  geometry: Apply LCHS values for boot devices

 src/Kconfig          |   7 ++
 src/block.c          |  18 +++-
 src/block.h          |   1 +
 src/boot.c           | 273 +++++++++++++++++++++++++++++++++++++++++----------
 src/hw/ahci.c        |   1 +
 src/hw/ata.c         |   8 ++
 src/hw/esp-scsi.c    |   2 +
 src/hw/lsi-scsi.c    |   2 +
 src/hw/megasas.c     |   1 +
 src/hw/mpt-scsi.c    |   2 +
 src/hw/pvscsi.c      |   1 +
 src/hw/virtio-blk.c  |   2 +
 src/hw/virtio-scsi.c |   2 +
 src/util.h           |   6 ++
 14 files changed, 272 insertions(+), 54 deletions(-)

-- 
2.13.3
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On Wed, Jun 26, 2019 at 03:38:11PM +0300, Sam Eiderman wrote:
> v1:
> 
> Non-standard logical geometries break under QEMU.
> 
> A virtual disk which contains an operating system which depends on
> logical geometries (consistent values being reported from BIOS INT13
> AH=08) will most likely break under QEMU/SeaBIOS if it has non-standard
> logical geometries - for example 56 SPT (sectors per track).
> No matter what QEMU will guess - SeaBIOS, for large enough disks - will
> use LBA translation, which will report 63 SPT instead.
> 
> In addition we can not enforce SeaBIOS to rely on phyiscal geometries at
> all. A virtio-blk-pci virtual disk with 255 phyiscal heads can not
> report more than 16 physical heads when moved to an IDE controller, the
> ATA spec allows a maximum of 16 heads - this is an artifact of
> virtualization.
> 
> By supplying the logical geometies directly we are able to support such
> "exotic" disks.
> 
> We will use fw_cfg to do just that.
> 
> v2:
> 
> Rename bootdevices fw_cfg key to bios-geoemtry
> 
> v3:
> 
> Change fw_cfg interface from mixed binary/textual to textual only
> Squash commit "config: Add toggle for bootdevice information"
> 
> v4:
> 
> * Rename TRANSLATION_MACHINE to TRANSLATION_HOST
> * Rename "overriden" translation name to "host-supplied"
> * Rename overriden_lchs_supplied() to host_lchs_supplied()
> * Move sectors and heads check to host_lchs_supplied()
> * Reuse duplicate code in boot.c

Looks all sane to me.

Usual workflow is to have to qemu bits merged first, so we'll go wait
for that.

cheers,
  Gerd
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