[libvirt] [Qemu-devel] [PATCH] cirrus_vga: adding sanity check for vram size

[Andreas Färber]

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Am 12.05.2014 19:05, schrieb Eric Blake:
> [adding libvirt]
> 
> On 05/09/2014 05:54 AM, Gerd Hoffmann wrote:
>> Hi,
>> 
>>> virt-manager/libvirt seems to default to 9 MByte of Vram for
>>> cirrus, so this would break a lot of setups.
>> 
>> It wouldn't.  libvirt sticks that into the xml, but it doesn't
>> set any qemu parameters.  The libvirt parameter actually predates
>> the qemu property for setting the size.

Déjà vu... we had the same problem with pvpanic.

> Then we should probably re-evaluate what libvirt does with the 
> parameters, which avoids breaking any guest that happens to be 
> pre-existing with the odd 9MB sizing in the XML.

If libvirt cannot or doesn't want to pass a user-supplied tag to QEMU,
the only sane and future-proof solution is for libvirt to signal an
error to the user for *any* flags it cannot handle rather than
throwing up on a case-by-case basis the question of how libvirt should
behave when some previously ignored feature gets implemented. That
would prevent us from running into this situation again and again.

As further examples, apic, acpi and other x86-centric features got
auto-added for s390x guests last time I checked. Apart from anything
the user might have specified herself, there's really no reason to add
stuff the user did not ask for and that are not applicable.

Ignoring a value "9" specified by the user would be very odd; and I
guess you have no way of telling who added what to the XML for
choosing between dropping and error'ing out.

Regards,
Andreas

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