qemu-img: Document copy offloading implications with -S and -c

Message ID 20180711012227.31600-1-famz@redhat.com
State New
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Series
  • qemu-img: Document copy offloading implications with -S and -c
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Commit Message

Fam Zheng July 11, 2018, 1:22 a.m.
Explicitly enabling zero detection or compression suppresses copy
offloading during convert. Document it.

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 qemu-img.texi | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Kevin Wolf July 11, 2018, 10:24 a.m. | #1
Am 11.07.2018 um 03:22 hat Fam Zheng geschrieben:
> Explicitly enabling zero detection or compression suppresses copy
> offloading during convert. Document it.
> 
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>

Thanks, applied to the block branch.

Kevin
Stefan Hajnoczi July 11, 2018, 1:27 p.m. | #2
On Wed, Jul 11, 2018 at 09:22:27AM +0800, Fam Zheng wrote:
> Explicitly enabling zero detection or compression suppresses copy
> offloading during convert. Document it.
> 
> Suggested-by: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  qemu-img.texi | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

Patch

diff --git a/qemu-img.texi b/qemu-img.texi
index aeb1b9e66c..5853cd18d1 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -96,7 +96,8 @@  will enumerate information about backing files in a disk image chain. Refer
 below for further description.
 
 @item -c
-indicates that target image must be compressed (qcow format only)
+indicates that target image must be compressed (qcow format only). If this
+option is used, copy offloading will not be attempted.
 
 @item -h
 with or without a command shows help and lists the supported formats
@@ -115,7 +116,8 @@  in case both @var{-q} and @var{-p} options are used.
 indicates the consecutive number of bytes that must contain only zeros
 for qemu-img to create a sparse image during conversion. This value is rounded
 down to the nearest 512 bytes. You may use the common size suffixes like
-@code{k} for kilobytes.
+@code{k} for kilobytes. If this option is used, copy offloading will not be
+attempted.
 
 @item -t @var{cache}
 specifies the cache mode that should be used with the (destination) file. See