Re: [Qemu-devel] [PATCH 4/4] blocksize: add blkconf_blocksize call to all block devices

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Thu, Sep 04, 2014 at 02:28:26PM +0400, Ekaterina Tumanova wrote:
> On 09/03/2014 07:46 PM, Stefan Hajnoczi wrote:
> >On Tue, Jul 29, 2014 at 02:27:19PM +0200, Ekaterina Tumanova wrote:
> >>This patch add the blkconf_blocksize call to all
> >>devices, which use DEFINE_BLOCK_PROPERTIES.
> >>If the underlying driver function fails, blkconf_blocksizes
> >>will set blocksizes to default (512) value.
> >>
> >>Signed-off-by: Ekaterina Tumanova <tumanova@linux.vnet.ibm.com>
> >>Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
> >>Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
> >>---
> >>  hw/block/nvme.c          | 1 +
> >>  hw/block/virtio-blk.c    | 1 +
> >>  hw/ide/qdev.c            | 1 +
> >>  hw/scsi/scsi-disk.c      | 1 +
> >>  hw/usb/dev-storage.c     | 1 +
> >>  include/hw/block/block.h | 4 ++--
> >>  6 files changed, 7 insertions(+), 2 deletions(-)
> >
> >Wasn't this NACKed before on the grounds that it is likely to upset the
> >guest after live migration?  QEMU doesn't automatically query the
> >storage because these parameters must be preserved across migration.
> >
> 
> Sorry, haven't found this discussion in the mail list. Do you have a link?

I don't have the link but am referring to the last time these patches
were discussed - ~1 year ago?

> As far as I understand, the xxxxxx_init functions of the qemu block devices,
> which contain blkconf_blocksize calls, will
> be called again on the destination host before the guest is resumed. And
> since migration requests qemu to be brought on the same disk, the
> configuration will receive the same block size from the ioctl, as
> before. What do I miss?

Live storage migration is supported.  This means non-shared storage is
possible.

Therefore the host block device that a guest runs on can change.

> >If you want specific parameters, please put them in your guest
> >configuration.  QEMU and libvirt support that.
> >
> >I'm concerned that this patch serious is likely to break things and
> >autodetection doesn't add much value since the management tool needs to
> >be aware of this information anyway.
> >
> 
> Can you please explain what do you mean by "AUTOdetection"?
> Do you simply mean "detection by ioctl" or "detection performed without
> guest request"?

I mean passing through the host block device attributes to the guest.

Stefan

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