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Re: [Qemu-devel] [PATCH v3 0/6] block: zero writes
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v3 0/6] block: zero writes |
Date: |
Wed, 21 Dec 2011 16:03:36 +0000 |
On Wed, Dec 21, 2011 at 4:00 PM, Stefan Hajnoczi
<address@hidden> wrote:
> This series adds an interface for efficient writes when data contains all
> zeros. It also takes advantage of this new interface by extending the
> copy-on-read feature to perform zero-detection.
>
> The details of efficient zero representations depend on the image format.
> This
> series includes a patch for the QED image format to write special "zero
> clusters" that keep the image file compact. In the future qcow2v3 could also
> support an efficient zero representation.
>
> The new BlockDriver interface is called .bdrv_co_write_zeroes() and is
> optional. If the interface is not implemented by a BlockDriver then a regular
> .bdrv_co_writev() operation will be performed. The public interface is called
> bdrv_co_write_zeroes() and can be tested via the new qemu-io write -z option.
>
> Copy-on-read is extended to detect zeroes and invoke the
> .bdrv_co_write_zeroes() interface when possible. As a result we avoid
> bloating
> the image file if the backing file contains zeroes.
>
> My motivation for this feature is efficient image streaming. The destination
> file must stay compact even when copying zeroes from the source file.
>
> We now only do zero detection for copy-on-read requests, whereas previous
> revisions of this patch series scanned all write requests for zeroes. The old
> behavior wasted CPU cycles in most cases but we could add a feature to
> explicitly scan guest writes for zeroes in the future, if desired.
>
> v2:
Typo:
s/v2/v3/
Stefan
- [Qemu-devel] [PATCH v3 1/6] cutils: extract buffer_is_zero() from qemu-img.c, (continued)
- [Qemu-devel] [PATCH v3 1/6] cutils: extract buffer_is_zero() from qemu-img.c, Stefan Hajnoczi, 2011/12/21
- [Qemu-devel] [PATCH v3 3/6] block: perform zero-detection during copy-on-read, Stefan Hajnoczi, 2011/12/21
- [Qemu-devel] [PATCH v3 4/6] qed: replace is_write with flags field, Stefan Hajnoczi, 2011/12/21
- [Qemu-devel] [PATCH v3 2/6] block: add .bdrv_co_write_zeroes() interface, Stefan Hajnoczi, 2011/12/21
- [Qemu-devel] [PATCH v3 5/6] qed: add .bdrv_co_write_zeroes() support, Stefan Hajnoczi, 2011/12/21
- [Qemu-devel] [PATCH v3 6/6] qemu-io: add write -z option for bdrv_co_write_zeroes, Stefan Hajnoczi, 2011/12/21
- Re: [Qemu-devel] [PATCH v3 0/6] block: zero writes,
Stefan Hajnoczi <=