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