Simplify the docs and reduce maintenance burden by just describing the algorithm by a pseudo-language. Users are encouraged to use libvirt anyways and projects such as oVirt which do some management of storage themselves are unlikely to use bash anyways. Signed-off-by: Peter Krempa <pkrempa@xxxxxxxxxx> --- docs/kbase/incrementalbackupinternals.rst | 44 ++++++----------------- 1 file changed, 11 insertions(+), 33 deletions(-) diff --git a/docs/kbase/incrementalbackupinternals.rst b/docs/kbase/incrementalbackupinternals.rst index c8a0a66baa..9a96ef6df3 100644 --- a/docs/kbase/incrementalbackupinternals.rst +++ b/docs/kbase/incrementalbackupinternals.rst @@ -228,42 +228,20 @@ following rules: Creating external snapshots manually -------------------------------------- -To create the same topology outside of libvirt (e.g when doing snapshots offline) -a new ``qemu-img`` which supports the ``bitmap`` subcommand is recommended. The -following algorithm then ensures that the new image after snapshot will work -with backups (note that ``jq`` is a JSON processor): +To create the same topology outside of libvirt (e.g when doing snapshots +offline) the following pseudo-algorithm ensures that the new image after +snapshot will work with backups. ``OVERLAY`` corresponds to the new overlay +image, ``ACTIVE`` corresponds to the topmost image of the active chain prior to +the snapshot. :: - #!/bin/bash + create image OVERLAY on top of ACTIVE - # arguments - SNAP_IMG="vda-2.qcow2" - BACKING_IMG="vda-1.qcow2" + for each BITMAP in ACTIVE: + let GRANULARITY = granularity of BITMAP in ACTIVE - # constants - snapshots and bitmaps work only with qcow2 - SNAP_FMT="qcow2" - BACKING_IMG_FMT="qcow2" + if BITMAP isn't RECORDING or is INCONSISTENT: + continue - # create snapshot overlay - qemu-img create -f "$SNAP_FMT" -F "$BACKING_IMG_FMT" -b "$BACKING_IMG" "$SNAP_IMG" - - BACKING_IMG_INFO=$(qemu-img info --output=json -f "$BACKING_IMG_FMT" "$BACKING_IMG") - BACKING_BITMAPS=$(jq '."format-specific".data.bitmaps' <<< "$BACKING_IMG_INFO") - - if [ "x$BACKING_BITMAPS" = "xnull" ]; then - exit 0 - fi - - for BACKING_BITMAP_ in $(jq -c '.[]' <<< "$BACKING_BITMAPS"); do - BITMAP_FLAGS=$(jq -c -r '.flags[]' <<< "$BACKING_BITMAP_") - BITMAP_NAME=$(jq -r '.name' <<< "$BACKING_BITMAP_") - - if grep 'in-use' <<< "$BITMAP_FLAGS" || - grep -v 'auto' <<< "$BITMAP_FLAGS"; then - continue - fi - - qemu-img bitmap -f "$SNAP_FMT" "$SNAP_IMG" --add "$BITMAP_NAME" - - done + create RECORDING bitmap named BITMAP in OVERLAY with GRANULARITY -- 2.26.2
