Re: [Qemu-devel] [QEMU] [PATCH v5 0/8] Add Qemu to SeaBIOS LCHS interface

[Gerd Hoffmann]

On Wed, Jun 26, 2019 at 03:39:40PM +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:
> 
> Fix missing parenthesis check in
>     "hd-geo-test: Add tests for lchs override"
> 
> v3:
> 
> * Rename fw_cfg key to "bios-geometry".
> * Remove "extendible" interface.
> * Add cpu_to_le32 fix as Laszlo suggested or big endian hosts
> * Fix last qtest commit - automatic docker tester for some reason does not 
> have qemu-img set
> 
> v4:
> 
> * Change fw_cfg interface from mixed textual/binary to textual only
> 
> v5:
> 
> * Fix line > 80 chars in tests/hd-geo-test.c

Reviewed-by: Gerd Hoffmann <address@hidden>

cheers,
  Gerd