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| author | Max Reitz <mreitz@redhat.com> | 2019-07-11 15:29:35 +0200 |
|---|---|---|
| committer | Max Reitz <mreitz@redhat.com> | 2019-08-19 17:13:26 +0200 |
| commit | fa27c478102a6b5d1c6b02c005607ad9404b915f (patch) | |
| tree | bd5aa3c5380cf84989c41bffd1e7e3bf28cb212a /qemu-img.texi | |
| parent | 9c46f4a06d9d57bc9f357cec3e37de94e6068413 (diff) | |
| download | qemu-fa27c478102a6b5d1c6b02c005607ad9404b915f.zip qemu-fa27c478102a6b5d1c6b02c005607ad9404b915f.tar.gz qemu-fa27c478102a6b5d1c6b02c005607ad9404b915f.tar.bz2 | |
doc: Preallocation does not require writing zeroes
When preallocating an encrypted qcow2 image, it just lets the protocol
driver write data and then does not mark the clusters as zero.
Therefore, reading this image will yield effectively random data.
As such, we have not fulfilled the promise of always writing zeroes when
preallocating an image in a while. It seems that nobody has really
cared, so change the documentation to conform to qemu's actual behavior.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190711132935.13070-1-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'qemu-img.texi')
| -rw-r--r-- | qemu-img.texi | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/qemu-img.texi b/qemu-img.texi index c8e9bba..b5156d6 100644 --- a/qemu-img.texi +++ b/qemu-img.texi @@ -666,8 +666,8 @@ Supported options: @item preallocation Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}). @code{falloc} mode preallocates space for image by calling posix_fallocate(). -@code{full} mode preallocates space for image by writing zeros to underlying -storage. +@code{full} mode preallocates space for image by writing data to underlying +storage. This data may or may not be zero, depending on the storage location. @end table @item qcow2 |