[PULL,3/7] qemu-img: Document copy offloading implications with -S and -c

Message ID 20180712163152.12521-4-kwolf@redhat.com
State New
Headers show
  • [PULL,1/7] iotests: 153: Fix dead code
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Commit Message

Kevin Wolf July 12, 2018, 4:31 p.m.
From: Fam Zheng <famz@redhat.com>

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>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
 qemu-img.texi | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)


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
 @item -t @var{cache}
 specifies the cache mode that should be used with the (destination) file. See