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Re: [Qemu-devel] [RFC v2 0/3] Q35/AHCI -cdrom/-hda desugaring


From: John Snow
Subject: Re: [Qemu-devel] [RFC v2 0/3] Q35/AHCI -cdrom/-hda desugaring
Date: Mon, 22 Sep 2014 19:17:12 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.0



On 09/19/2014 05:53 AM, Markus Armbruster wrote:
John Snow <address@hidden> writes:

This is an extremely rough/quick sketch of
a -cdrom/-hda desugaring fix for Q35/AHCI.

Before I spent any time on it, I wanted feedback
from Markus or anyone else who had concerns about
how this problem would get fixed.

This is, then, rough approach #2.

Highlights:
(1) Add a board property (instead of a HBA property, sigh)
     that defines how we should map (index, (bus,unit)).

Imperfect, but it'll do for now.  The place in the boards that sets it
should point to the HBA in a comment.

(2) Modify drive_new to accept the MachineClass instead of
     the default interface type. This does not affect how
     default drives get added, because any over-rides to
     the "default type" get handled in options, so while
     it appears we have removed the type of default drives,
     we have not.

(3) Create helpers for AHCI to assist the Q35 board in
     populating the AHCI device with the IDE drives.

(4) Create a helper to whine at us for oversights and
     help bug reporters give us more meaningful information.

General approach looks good to me; I can see only coding bugs, not
design flaws.


I rewrote this series and was about to send it out, but it does fail the bios-tables-test because this test uses this command line:

-net none -display none -machine q35,accel=tcg -drive file=tests/acpi-test-disk.raw,id=hd0 -device ide-hd,drive=hd0,

Notice it doesn't say if=none for the drive, so after fixing Q35, this actually creates a new failure in this test because we will create the drive (and device), then fail when trying to create the second device attached to the same drive.

I think this test is at fault, but I wanted to be duly diligent and ask the question: "Is it a big deal if I break backwards compatibility with broken scripts?"

--
—js



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