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From: Gerd Hoffmann <kraxel@redhat.com>
To: Sam Eiderman <shmuel.eiderman@oracle.com>
Cc: kwolf@redhat.com, qemu-block@nongnu.org, arbel.moshe@oracle.com,
	seabios@seabios.org, QEMU <qemu-devel@nongnu.org>,
	mreitz@redhat.com, kevin@koconnor.net, liran.alon@oracle.com,
	karl.heubaum@oracle.com
Subject: Re: [Qemu-devel] [QEMU] [PATCH v2 0/8] Add Qemu to SeaBIOS LCHS interface
Date: Thu, 13 Jun 2019 11:38:50 +0200	[thread overview]
Message-ID: <20190613093850.5k7prawn6x4qt3fi@sirius.home.kraxel.org> (raw)
In-Reply-To: <02844D7D-ED79-4744-A203-8E713DE7A717@oracle.com>

  Hi,

> Yes they are pretty rare.
> Windows 2000 and Windows XP guests migrated from VMware to Qemu/KVM
> would not boot due to incorrect disk geometries (some had 32/56 spt instead of
> 56. Also number of heads was not entirely correct)

Ok.

> > Why?  Asking the user to deal with the mess is pretty lame if there are
> > better options.  And IMO doing this fully automatic in seabios is
> > better.
> 
> I’m not against an automatic approach, however I do think that doing this
> in SeaBIOS might break compatibility for already existing guests that will
> suddenly see different LCHS values. (Explanation below)

> > I can't see how this can break guests.  It should either have no effect
> > (guests using LBA) or unbreak guests due to LCHS changing from "wrong"
> > to "correct”.
> 
> I’m not sure what do you mean by "unbreak guests” if you change an existing
> guest that uses LCHS from 56 spt to LBA (63 spt) it will stop booting.

Well, that LCHS change happens because you move the guest from vmware to
qemu and seabios uses 63 spt no matter what if the disk is too big for
chs addressing.

When seabios is changed to look at the MBR to figure what the lchs of
the disk is that will make your guest boot.

> Your guessing algorithm will have to guess 56, if it will fail guessing 56 correctly,
> the user can not perform any action beside downgrading SeaBIOS in order to run
> the guest.

Sure, if the guess is wrong then the guest will not boot.  That isn't
worse than the situation we have today where seabios will not even try
to figure what the lchs of the disk is.

And, no, downgrading seabios will not make your vmware guest with 56 spt
boot.

cheers,
  Gerd



  parent reply	other threads:[~2019-06-13  9:48 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 11:59 [Qemu-devel] [QEMU] [PATCH v2 0/8] Add Qemu to SeaBIOS LCHS interface Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 1/8] block: Refactor macros - fix tabbing Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 2/8] block: Support providing LCHS from user Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 3/8] bootdevice: Add interface to gather LCHS Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 4/8] scsi: Propagate unrealize() callback to scsi-hd Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 5/8] bootdevice: Gather LCHS from all relevant devices Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 6/8] bootdevice: Refactor get_boot_devices_list Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 7/8] bootdevice: FW_CFG interface for LCHS values Sam Eiderman
2019-06-17  7:20   ` Gerd Hoffmann
2019-06-17  7:36     ` Sam Eiderman
2019-06-17  8:38       ` Gerd Hoffmann
2019-06-17 10:08         ` Sam Eiderman
2019-06-17 14:48       ` Kevin O'Connor
2019-06-17 15:13         ` Sam Eiderman
2019-06-12 11:59 ` [Qemu-devel] [QEMU] [PATCH v2 8/8] hd-geo-test: Add tests for lchs override Sam Eiderman
2019-06-12 12:33 ` [Qemu-devel] [SeaBIOS] [QEMU] [PATCH v2 0/8] Add Qemu to SeaBIOS LCHS interface no-reply
2019-06-12 13:06 ` [Qemu-devel] " Gerd Hoffmann
2019-06-12 13:30   ` Sam Eiderman
2019-06-12 19:18     ` Gerd Hoffmann
2019-06-13  7:41       ` Sam Eiderman
2019-06-13  7:44         ` Sam Eiderman
2019-06-13  9:38         ` Gerd Hoffmann [this message]
2019-06-13 11:45           ` Sam Eiderman
2019-06-14  4:43             ` Gerd Hoffmann
2019-06-14  9:37               ` Sam Eiderman
2019-06-17  6:50                 ` Gerd Hoffmann
2019-06-17  7:59                   ` Sam Eiderman
2019-06-12 13:51 ` [Qemu-devel] [SeaBIOS] " no-reply

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