Changes

Patchset teaches criu primitives to work with dynamically allocated pids, sids, pgids and threads ids, and allows them to have up to 32 nesting level (current maximal level from Linux kernel). It makes pids (etc) be linked on every ns_id::pid::rb_root instead of global one-level pid_root_rb's rb_node, and this allows to find a free pid on the whole pid ns hierarchy. Before the patchset we used pids (etc) given by parasite, now we get them from NSpid (etc) strings in /proc/[pid]/status, if there are several pid namespaces.

Patchset teaches criu primitives to work with dynamically allocated pids, sids, pgids and threads ids, and allows them to have up to 32 nesting level (current maximal level from Linux kernel). It makes pids (etc) be linked on every ns_id::pid::rb_root instead of global one-level pid_root_rb's rb_node, and this allows to find a free pid on the whole pid ns hierarchy. Before the patchset we used pids (etc) given by parasite, now we get them from NSpid (etc) strings in /proc/[pid]/status, if there are several pid namespaces.

One more thing the patchset does, is unification of pstree_item::ids. We have many always checks like "if (item->ids->has_xxx_ns_id)", and they are noisy and over the whole code. The patchset determines and populates not existing ids for the tasks in single place on the stage of image reading. So, after the patchset we'll be able to delete all of these noisy checks and make the code simply and more beautiful.

One more thing, the patchset does, is unification of pstree_item::ids. We have many always checks like "if (item->ids->has_xxx_ns_id)", and they are noisy and over the whole code. The patchset determines and populates not existing ids for the tasks in single place on the stage of image reading. So, after the patchset we'll be able to delete all of these noisy checks and make the code simply and more beautiful. The patchset itself needs this to know, which pid_ns a task belongs to.