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kbase: improve disk image chains documentation
1. Use 'setup' consistently as noun, 'set up' as verb 2. Use path variables like '$IMAGE_PATH' consistently like in Troubleshooting to improve readability 3. Remove ':' from field names 4. Change phrasing in sentences I stumbled upon several times to improve readability. 5. Minor grammar/vocab fixes. Signed-off-by: Sebastian Mitterle <smitterl@redhat.com> Reviewed-by: Peter Krempa <pkrempa@redhat.com>
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@ -38,12 +38,12 @@ image of the backing chain.
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This configuration will prompt libvirt to detect the backing image of the source
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image and recursively do the same thing until the end of the chain.
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Importance of properly setup backing chain
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------------------------------------------
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Importance of proper backing chain setup
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----------------------------------------
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The disk image locations are used by libvirt to properly set up the security
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system used on the host so that the hypervisor can access the files and possibly
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also directly to configure the hypervisor to use the appropriate images. Thus
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system used on the host so that the hypervisor can access the files; it can
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also be used to configure the hypervisor to use the appropriate images. Thus
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it's important to properly set up the formats and paths of the backing images.
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Any externally created image should always use the -F switch of ``qemu-img``
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@ -60,7 +60,7 @@ explicitly in the XML or the overlay image itself.
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Libvirt also might lack support for a network disk storage technology and thus
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may be unable to visit and detect backing chains on such storage. This may
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result in the backing chain present in the live XML to look incomplete or some
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result in the backing chain in the live XML looking incomplete or some
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operations not being possible. To prevent this it's possible to specify the
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image metadata explicitly in the XML.
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@ -104,7 +104,7 @@ An empty ``<backingStore/>`` element signals the end of the chain. Using this
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will prevent libvirt or qemu from probing the backing chain.
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Note that it's also possible to partially specify the chain in the XML but omit
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the terminating element. This will result into probing from the last specified
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the terminating element. This will result in probing from the last specified
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``<backingStore>``
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Any image specified explicitly will not be probed for backing file or format.
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@ -120,10 +120,10 @@ means that the **-F** parameter of ``qemu-img`` must always be used.
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::
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qemu-img -f qcow2 -F qcow2 -b /path/to/backing /path/to/overlay
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qemu-img -f qcow2 -F qcow2 -b $BACKING_IMAGE_PATH $IMAGE_PATH
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Note that if '/path/to/backing' is relative the path is considered relative to
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the location of '/path/to/overlay'.
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Note that if ``$BACKING_IMAGE_PATH`` is relative the path is considered relative to
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the location of ``$IMAGE_PATH``.
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Troubleshooting
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===============
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@ -164,7 +164,7 @@ the image has a backing image format specified:
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refcount bits: 16
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corrupt: false
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If the ``backing file format:`` field is missing above the format was not
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If the ``backing file format`` field is missing above the format was not
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specified properly. The image can be fixed by the following command:
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::
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@ -177,22 +177,22 @@ If relative referencing of the backing image is desired, the path must be
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relative to the location of image described by ``$IMAGE_PATH``.
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**Important:** If the ``$BACKING_IMAGE_FORMAT`` is not known it can be queried
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using ``qemu-img info $BACKING_IMAGE_PATH`` and looking for the ``file format:``
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field, but for security reasons should be used *only* if at least one of the
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following criteria is met:
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using ``qemu-img info $BACKING_IMAGE_PATH`` and looking for the ``file format``
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field, but for security reasons the value should be used *only* if at least one
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of the following criteria is met:
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- ``file format`` is ``raw``
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- ``backing file`` is NOT present
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- ``backing file`` is present AND is correct/trusted
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Note that the last criteria may require manual inspection and thus should not
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Note that the last criterion may require manual inspection and thus should not
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be scripted unless the trust for the image can be expressed programatically.
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Also note that the above steps may need to be repeated recursively for any
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subsequent backing images.
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Missing images reported after after moving disk images into a different path
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----------------------------------------------------------------------------
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Missing images reported after moving disk images into a different path
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----------------------------------------------------------------------
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The path to the backing image which is recorded in the image metadata often
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contains a full path to the backing image. This is the default libvirt-created
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