12:05 p.m.
[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.
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.
> Looking at datasheets on the web seems to say the chips actually
went
> down to 1 MB or less.
I have my doubts we emulate that correctly (register telling the guest
how much memory is actually there etc.). Also it is pretty much useless
these days, even the 4MB imply serious constrains when FullHD displays
are commonplace. Newer cirrus drivers such as the kernel's drm driver
are specifically written to qemu's cirrus cards, I have my doubs that
they are prepared to handle 1MB cirrus cards correctly.
Bottom line: Allowing less than 4MB is asking for trouble for no good
reason ;)
cheers,
Gerd
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
12:53 p.m.
New subject: [libvirt] [Qemu-devel] [PATCH] cirrus_vga: adding sanity check for vram size
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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
- --
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg
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