We must build up the inode list with the extent lock held after following
indirect refs.

This also requires an extension to ulists, which allows to modify the stored
aux value in case a key already exists in the list.
Signed-off-by: NJan Schmidt <list.btrfs@jan-o-sch.net>

ulist_next gets the pointer to the previously returned element to find the
next element from there. However, when we call ulist_add while iteration
with ulist_next is in progress (ulist explicitly supports this), we can
realloc the ulist internal memory, which makes the pointer to the previous
element useless.

Instead, we now use an iterator parameter that's independent from the
internal pointers.
Reported-by: NAlexander Block <ablock84@googlemail.com>
Signed-off-by: NJan Schmidt <list.btrfs@jan-o-sch.net>

ulist is a generic data structures to hold a collection of unique u64
values. The only operations it supports is adding to the list and
enumerating it.

It is possible to store an auxiliary value along with the key. The
implementation is preliminary and can probably be sped up significantly.

It is used by btrfs_find_all_roots() quota to translate recursions into
iterative loops.
Signed-off-by: NArne Jansen <sensille@gmx.net>
Signed-off-by: NJan Schmidt <list.btrfs@jan-o-sch.net>