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Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector |
Date: |
Wed, 13 May 2015 23:47:48 +0200 |
On Wed, May 13, 2015 at 08:57:00PM +0200, Christian Borntraeger wrote:
> Am 13.05.2015 um 18:14 schrieb Michael S. Tsirkin:
> >> - AFAICS, there's no easy way to add transport-specific subsections -
> >> and simply adding config_vector in ccw would break compatibility
> >
> > subsections break compatibility too. The only way around that is to set
> > a flag to skip migrating config_vector for old machine types.
>
> My main concern is about undetected compatibility issues. A subsection will
> tell the user that something went wrong. What happens if we just add a new
> qemu_put_byte in the stream. Will the savevm core always detect that we have
> too many or not enough bytes? If yes, adding new stuff in the stream will
> always be detected in some way as error we can go with just adding
> qemu_put_be16/qemu_get_be16 in virtio_ccw_save_config/virtio_ccw_load_config.
> Old/new QEMUs will then not be compatible - but thats probably ok as long as
> it
> errors out.
>
> My understanding was that we do not have a guarentee that this will be
> detected all the time and having random junk in some variables is a debugging
> nightmare. Is that correct?
>
>
> Christian
It's not too bad - normally there's a bunch of strings that
helps you find out what's going on.
But if you really care about debuggability of migration streams, help move
forward dgilbert's RFC that switched to a self-delimiting format.
Just piling up random hacks in virtio seems like a wrong approach.
--
MST
- [Qemu-devel] [PATCH RFC 0/1] virtio: fix config_vector migration issues, Cornelia Huck, 2015/05/13
- [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Cornelia Huck, 2015/05/13
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Michael S. Tsirkin, 2015/05/13
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Cornelia Huck, 2015/05/13
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Michael S. Tsirkin, 2015/05/13
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Christian Borntraeger, 2015/05/13
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Christian Borntraeger, 2015/05/14
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Michael S. Tsirkin, 2015/05/14
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Paolo Bonzini, 2015/05/14
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Christian Borntraeger, 2015/05/14
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Dr. David Alan Gilbert, 2015/05/14
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Christian Borntraeger, 2015/05/15
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Michael S. Tsirkin, 2015/05/15
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Cornelia Huck, 2015/05/18
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Cornelia Huck, 2015/05/18
- Re: [Qemu-devel] [PATCH RFC 1/1] virtio: migrate config_vector, Paolo Bonzini, 2015/05/14