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And here is the example of order inversion where multiple temporary mounts needed to achieve the result:
And here is the example of order inversion where multiple temporary mounts needed to achieve the result:
[[File:Mounts-inverse-order-example.gif|none|link=|Mounts-inverse-order-example.gif]]
[[File:Mounts-inverse-order-example.gif|none|link=|Mounts-inverse-order-example.gif]]
== Mount-v2 description ==
New mount-v2 algorithm is integrated deeply in the original one, so that dumping of mounts is done exactly the same for original mount engine and new one. So mount-v2 series has preparatory steps related to bindmount detection, external mounts detection and helper mounts handling to make the original mount code more robust, to make it easier to reuse it in mount-v2.
One of main differences of mount-v2 comparing to original is that mounts are initially created "plain", for instance if we had '''MOUNT''' with '''mnt_id=1000''' and '''ns_mountpoint="/mount/point/path"''', original mount engine would originally mount this '''MOUNT''' in the mount tree to '''<criu_root_yard>/<mntns>/mount/point/path''' so that if this mount had '''PARENT''' mount with '''mnt_id=999''' and '''ns_mountpoint="/mount/point"''' corresponding mount for '''PARENT''' would be created in '''<criu_root_yard>/<mntns>/mount/point''' thus restoring parent-child relationship between them initially. For mount-v2 '''MOUNT''' would be first mounted to '''<criu_root_yard>/mnt-1000''' and '''PARENT''' would be mounted to '''<criu_root_yard>/mnt-999''' so that on the first stage we only create mounts and then on separate second stage handle the tree assembling separately. This way we can have useful heuristics like on the second stage we can create overmounts after mounts they overmount, and on the first stage we can create external mounts before their bindmounts and these two do not clinch with each other.
But it is not so simple actually because we do not want to rewrite all the code for instance for restoring mount content or restoring ghost and remap files, which used mountpoint paths in "tree" format. So in all places where it does not matter (where we do not access <criu_root_yard>/<mntns>/... paths) we switched from using mount_info->mountpoint to mount_info->ns_mountpoint and in all places where we actually needed "tree" format paths we replace them with service_mountpoint() helper which would return "tree" paths for original mount engine and "plain" paths for mount-v2. This way we can safely switch from one to another.
to be continued...
to be continued...