From: Paolo Bonzini <pbonzini@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: amit.shah@redhat.com, uobergfe@redhat.com, owasserm@redhat.com,
qemu-devel@nongnu.org, armbru@redhat.com
Subject: Re: [Qemu-devel] [PATCH 1/3] virtio: let devices be permissive on enabled features
Date: Tue, 06 Mar 2012 14:57:26 +0100 [thread overview]
Message-ID: <4F5617C6.9020107@redhat.com> (raw)
In-Reply-To: <20120306133331.GB12096@redhat.com>
Il 06/03/2012 14:33, Michael S. Tsirkin ha scritto:
>> > virtio_load checks features that are enabled by the guest and
>> > blocks migration if they are not available in the destination
>> > host. However, in some cases we can let features through because
>> > we know that guests will be able to proceed even without it.
>> >
>> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>
> So why do we need these hacks? You are saying things
> work fine without this information. Then,
> why not just have the bit set in supported features always?
Not sure what you mean.
virtio-balloon works fine only because our implementation does not set
the bit. I found it just by inspection, but it's wrong. If QEMU
started setting VIRTIO_F_BALLOON_MUST_TELL_HOST, migration would fail to
a version that does not set it.
virtio-blk is what prompted the patch and it is a real bug. Updating
libvirt on the destination causes the source's scsi=on to become
scsi=off on the destination. Then migration fails (it used to crash,
Orit fixed the crash, I'm fixing the rest). However, a kernel update
can cause the same behavioral change can happen even if
VIRTIO_BLK_F_SCSI remains on, so it is not a good reason to fail migration.
Paolo
next prev parent reply other threads:[~2012-03-06 13:57 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-06 12:22 [Qemu-devel] [PATCH 0/3] Make virtio_load permissive when possible Paolo Bonzini
2012-03-06 12:22 ` [Qemu-devel] [PATCH 1/3] virtio: let devices be permissive on enabled features Paolo Bonzini
2012-03-06 13:33 ` Michael S. Tsirkin
2012-03-06 13:57 ` Paolo Bonzini [this message]
2012-03-06 14:22 ` Orit Wasserman
2012-03-06 12:22 ` [Qemu-devel] [PATCH 2/3] virtio-balloon: note optional features Paolo Bonzini
2012-03-06 14:55 ` Michael S. Tsirkin
2012-03-06 14:59 ` Paolo Bonzini
2012-03-06 15:08 ` Michael S. Tsirkin
2012-03-06 15:13 ` Paolo Bonzini
2012-03-06 12:22 ` [Qemu-devel] [PATCH 3/3] virtio-blk: " Paolo Bonzini
2012-03-06 14:53 ` Michael S. Tsirkin
2012-03-06 15:58 ` Paolo Bonzini
2012-03-06 17:03 ` Anthony Liguori
2012-03-06 17:12 ` Paolo Bonzini
2012-03-06 17:15 ` Anthony Liguori
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