Re: [Qemu-devel] [PATCH v2] qdev: Keep global allocation counter per bus

[Markus Armbruster <armbru@redhat.com>]

Peter Crosthwaite <peter.crosthwaite@xilinx.com> writes:

> On Wed, Jan 8, 2014 at 2:59 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 07/01/2014 16:12, Markus Armbruster ha scritto:
>>>     aarch64     akita           info qtree crashes
>>>     aarch64     borzoi          info qtree crashes
>>>     aarch64     spitz           info qtree crashes
>>>     aarch64     terrier         info qtree crashes
>>>     aarch64     tosa            info qtree crashes
>>>     arm         akita           info qtree crashes
>>>     arm         borzoi          info qtree crashes
>>>     arm         spitz           info qtree crashes
>>>     arm         terrier         info qtree crashes
>>>     arm         tosa            info qtree crashes
>>>     cris        axis-dev88      info qtree crashes
>>
>> The crash is because of commit 7426aa7 (nand: Don't inherit from Sysbus,
>> 2013-06-18).   Should probably be reverted.
>>
>
> Prefer not, under no reasonable definition is NAND a sysbus device.
> Whats the real problem here? What is TYPE_SYS_BUS_DEVICE doing WRT to
> qtree that TYPE_DEVICE is not?

Maybe, but our definition of sysbus has never been reasonable :)

Qdev, as designed by Paul Brook, assumed the parent of a qdev is always
a qbus and vice versa.  With the exception of the root, which has no
parent, and is a sysbus, commonly the only one.

A PCI qdev plugs into a PCI qbus, an USB qdev plugs into an USB qbus,
and so forth.  Any qdev that doesn't really plug into a bus was made a
"sysbus device" by fiat.  "Sysbus" is a catchall, no more.  In
particular, it's not a bus in the hardware sense.

This "everything plugs into exactly one bus" assumption is of course a
gross oversimplification, and we've been working on overcoming it for
quite some time.  It has become possible to define qdevs that aren't
connected to a qbus.  A TYPE_DEVICE isn't.

That's progress.  But progress isn't justification for not fixing crash
bugs in monitor commands.

Either you fix "info qtree" to cope with your change to the device
graph, or the change needs to be reverted until somebody fixes it or it
goes away.