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docs: Make the recommendation for the backing file name position a requirement

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The current version of the qcow2 specification recommends to save the backing
file name in the end of the first cluster. It follows that the backing file
name can be saved somewhere in the image, but the first cluster, which
contradicts the current QEMU implementation.

The patch makes the backing file name required to be placed after the header
extensions in the first image cluster.

Signed-off-by: Maria Kustova <maria.k@catit.be>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Maria Kustova 2014-07-21 15:16:33 +04:00 committed by Kevin Wolf
parent 52bf1e722d
commit 8e436ec1f3
1 changed files with 6 additions and 6 deletions
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12
docs/specs/qcow2.txt
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@ -135,12 +135,12 @@ be stored. Each extension has a structure like the following:
Unless stated otherwise, each header extension type shall appear at most once Unless stated otherwise, each header extension type shall appear at most once
in the same image. in the same image.
The remaining space between the end of the header extension area and the end of If the image has a backing file then the backing file name should be stored in
the first cluster can be used for the backing file name. It is not allowed to the remaining space between the end of the header extension area and the end of
store other data here, so that an implementation can safely modify the header the first cluster. It is not allowed to store other data here, so that an
and add extensions without harming data of compatible features that it implementation can safely modify the header and add extensions without harming
doesn't support. Compatible features that need space for additional data can data of compatible features that it doesn't support. Compatible features that
use a header extension. need space for additional data can use a header extension.
== Feature name table == == Feature name table ==