[PATCH 0/6][RFC] user-cr: restart: Make task table portable

[Matt Helsley]

This series modifies the task table entries to use indexes rather than
pointers to create the tree. This is one step that enables the same
table to be shared between multiple restart processes regardless of
whether they are 32 or 64-bit.

Further steps, not in this set, include:
	1. Mark bitness of each task in the table.
	2. Share the table contents.
		Probably via an fd passed during execve() then mmap()'ed
	3. Find/modify restart to do execve() at the right spot.

The patches:
	1/6 Make context global
	2/6 Replace children pointer with index
	3/6 Replace next_sib pointer with an index
	4/6 Replace prev_sib pointer with index
	5/6 Replace phantom pointer with index
	6/6 Replace creator pointer with index

Each patch converts one of the fields to an index while leaving the
others untouched. Should be bisect safe, but feel free to merge the
patches if you like.

(These are RFC since they aren't properly tested and don't actually
make restart do the 32/64-bit transitions but feel free to include
them if you like.)

Cheers,
	-Matt Helsley