Re: [Qemu-devel] [PATCH 2/2] machine_parse(): list supported machine types in their registration order

[Marcel Apfelbaum]

On Mon, 2014-09-22 at 15:36 +0300, Michael S. Tsirkin wrote:
> On Mon, Sep 22, 2014 at 02:29:08PM +0200, Laszlo Ersek wrote:
> > On 09/22/14 14:04, Andreas Färber wrote:
> > > Am 22.09.2014 um 13:26 schrieb Laszlo Ersek:
> > >> Based on the registration order captured in the previous patch, we
> > >> sort the ad-hoc list printed for
> > >>
> > >>   qemu-system-XXXX -M \?
> > >
> > > Agree that the order is worth sanitizing. I would however argue that
> > > registration order is not entirely stable either if you think of
> > > non-PC cases where there's dozens of source files registering one
> > > machine each. I would therefore propose alphabetical order as we do
> > > for QOM'ified CPUs.
> > 
> > I did mention alphabetical order in the message of patch #1 -- in fact
> > that was what I implemented first:
> > 
> > > The first idea to restore ordering is to sort the ad-hoc list in
> > > machine_parse() by "MachineClass.name". Such a name-based ordering
> > > would have to be reverse, so that more recent versioned machine types
> > > appear higher on the list than older versioned machine types (eg. with
> > > qemu-system-x86_64). However, such a reverse sort wreaks havoc between
> > > non-versioned machine types (such as those of qemu-system-aarch64).
> > 
> > Simply put, it looks very ugly. Namely, if you sort it in alphabetically
> > *ascending* order, then for the x86_64 target, you get:
> > 
> > > isapc                ISA-only PC
> > > none                 empty machine
> > > pc                   Standard PC (i440FX + PIIX, 1996) (alias of 
> > > pc-i440fx-2.2)
> > > pc-0.10              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.11              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.12              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.13              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.14              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.15              Standard PC (i440FX + PIIX, 1996)
> > > pc-1.0               Standard PC (i440FX + PIIX, 1996)
> > > pc-1.1               Standard PC (i440FX + PIIX, 1996)
> > > pc-1.2               Standard PC (i440FX + PIIX, 1996)
> > > pc-1.3               Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.4        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.5        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.6        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.7        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-2.0        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-2.1        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-2.2        Standard PC (i440FX + PIIX, 1996) (default)
> > > pc-q35-1.4           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-1.5           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-1.6           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-1.7           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-2.0           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-2.1           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-2.2           Standard PC (Q35 + ICH9, 2009)
> > > q35                  Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-2.2)
> > 
> > which is very bad / unusual. Okay, so let's sort it in alphabetically
> > descending order:
> > 
> > > q35                  Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-2.2)
> > > pc-q35-2.2           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-2.1           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-2.0           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-1.7           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-1.6           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-1.5           Standard PC (Q35 + ICH9, 2009)
> > > pc-q35-1.4           Standard PC (Q35 + ICH9, 2009)
> > > pc-i440fx-2.2        Standard PC (i440FX + PIIX, 1996) (default)
> > > pc-i440fx-2.1        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-2.0        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.7        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.6        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.5        Standard PC (i440FX + PIIX, 1996)
> > > pc-i440fx-1.4        Standard PC (i440FX + PIIX, 1996)
> > > pc-1.3               Standard PC (i440FX + PIIX, 1996)
> > > pc-1.2               Standard PC (i440FX + PIIX, 1996)
> > > pc-1.1               Standard PC (i440FX + PIIX, 1996)
> > > pc-1.0               Standard PC (i440FX + PIIX, 1996)
> > > pc-0.15              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.14              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.13              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.12              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.11              Standard PC (i440FX + PIIX, 1996)
> > > pc-0.10              Standard PC (i440FX + PIIX, 1996)
> > > pc                   Standard PC (i440FX + PIIX, 1996) (alias of 
> > > pc-i440fx-2.2)
> > > none                 empty machine
> > > isapc                ISA-only PC
> > 
> > Okay, this is certainly bearable. However, let's see what the reverse
> > alpha sort does to aarch64:
> > 
> > > z2                   Zipit Z2 (PXA27x)
> > > xilinx-zynq-a9       Xilinx Zynq Platform Baseboard for Cortex-A9
> > > virt                 ARM Virtual Machine
> > > vexpress-a9          ARM Versatile Express for Cortex-A9
> > > vexpress-a15         ARM Versatile Express for Cortex-A15
> > > versatilepb          ARM Versatile/PB (ARM926EJ-S)
> > > versatileab          ARM Versatile/AB (ARM926EJ-S)
> > > verdex               Gumstix Verdex (PXA270)
> > > tosa                 Tosa PDA (PXA255)
> > > terrier              Terrier PDA (PXA270)
> > > sx1-v1               Siemens SX1 (OMAP310) V1
> > > sx1                  Siemens SX1 (OMAP310) V2
> > > spitz                Spitz PDA (PXA270)
> > > smdkc210             Samsung SMDKC210 board (Exynos4210)
> > > realview-pbx-a9      ARM RealView Platform Baseboard Explore for Cortex-A9
> > > realview-pb-a8       ARM RealView Platform Baseboard for Cortex-A8
> > > realview-eb-mpcore   ARM RealView Emulation Baseboard (ARM11MPCore)
> > > realview-eb          ARM RealView Emulation Baseboard (ARM926EJ-S)
> > > nuri                 Samsung NURI board (Exynos4210)
> > > none                 empty machine
> > > n810                 Nokia N810 tablet aka. RX-44 (OMAP2420)
> > > n800                 Nokia N800 tablet aka. RX-34 (OMAP2420)
> > > musicpal             Marvell 88w8618 / MusicPal (ARM926EJ-S)
> > > midway               Calxeda Midway (ECX-2000)
> > > mainstone            Mainstone II (PXA27x)
> > > lm3s811evb           Stellaris LM3S811EVB
> > > lm3s6965evb          Stellaris LM3S6965EVB
> > > kzm                  ARM KZM Emulation Baseboard (ARM1136)
> > > integratorcp         ARM Integrator/CP (ARM926EJ-S)
> > > highbank             Calxeda Highbank (ECX-1000)
> > > cubieboard           cubietech cubieboard
> > > connex               Gumstix Connex (PXA255)
> > > collie               Collie PDA (SA-1110)
> > > cheetah              Palm Tungsten|E aka. Cheetah PDA (OMAP310)
> > > canon-a1100          Canon PowerShot A1100 IS
> > > borzoi               Borzoi PDA (PXA270)
> > > akita                Akita PDA (PXA270)
> > 
> > Ugh? The reverse sort is painfully obvious, and the user wonders why it
> > is necessary. Why is z2 at the top, and akita at the bottom? Why is n810
> > above n800 and not below it? And so on.
> >
> > Instead, the patchset restores the behavior that had been visible before
> > commit 261747f1: programmer-controlled logical order *within* clusters,
> > and unspecified order *between* clusters.
> 
> We could add a cluster name in the API.
> Use that for sort between clusters only.
> Hmm?
Since the machines have now QOM types we can leverage the types
as "clusters", and each machine hierarchy can have its own
sorting interface to arrange their descendants however is desired.

It will look like:
1. Get all machine types that implement "sort" interface.
2. Define a sort order between them (a interface property ?)
3. Ask for each of them to sort its descendants.

In this way we have maximum control on the output and
give each cluster a proper way to decide the ordering
based on the semantics and not alphabetical/registering order. 

Thanks,
Marcel 

> 
> > IOW, I tested your idea (because it was my first idea as well), and I
> > thought (and still think) that alpha sort is inferior to the
> > pre-261747f1 order.
> > 
> > Thanks,
> > Laszlo