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Re: [Qemu-block] [SeaBIOS] [PATCH v4 0/5] Add Qemu to SeaBIOS LCHS inter

From: Gerd Hoffmann
Subject: Re: [Qemu-block] [SeaBIOS] [PATCH v4 0/5] Add Qemu to SeaBIOS LCHS interface
Date: Mon, 1 Jul 2019 09:44:51 +0200
User-agent: NeoMutt/20180716

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 "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.


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