Re: [Qemu-devel] [PATCH 2/2] NBD proto: add GET_LBA_STATUS extension

[Eric Blake <eblake@redhat.com>]

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On 03/23/2016 08:16 AM, Denis V. Lunev wrote:
> From: Pavel Borzenkov <pborzenkov@virtuozzo.com>
> 
> With the availability of sparse storage formats, it is often needed to
> query status of a particular LBA range and read only those blocks of
> data that are actually present on the block device.
> 
> To provide such information, the patch adds GET_LBA_STATUS extension
> with one new NBD_CMD_GET_LBA_STATUS command.
> 
> There exists a concept of data dirtiness, which is required during, for
> example, incremental block device backup. To express this concept via
> NBD protocol, this patch also adds additional mode of operation to
> NBD_CMD_GET_LBA_STATUS command.
> 
> Since NBD protocol has no notion of block size, and to mimic SCSI "GET
> LBA STATUS" command more closely, it has been chosen to return a list of
> extents in the response of NBD_CMD_GET_LBA_STATUS command, instead of a
> bitmap.
> 
> Signed-off-by: Pavel Borzenkov <pborzenkov@virtuozzo.com>
> Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Wouter Verhelst <w@uter.be>
> CC: Paolo Bonzini <pbonzini@redhat.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  doc/proto.md | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 82 insertions(+)

I've posted a v2 of this proposal under a new title, rebased on top of
the recent work to add structured replies, and trying to take into
account a number of the suggestions that occurred in this thread.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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