bcachefs: node scan: ignore multiple nodes with same seq if interior

Interior nodes are not really needed, when we have to scan - but if this
pops up for leaf nodes we'll need a real heuristic.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: bch_member.btree_allocated_bitmap

This adds a small (64 bit) per-device bitmap that tracks ranges that
have btree nodes, for accelerating btree node scan if it is ever needed.

- New helpers, bch2_dev_btree_bitmap_marked() and
bch2_dev_bitmap_mark(), for checking and updating the bitmap

- Interior btree update path updates the bitmaps when required

- The check_allocations pass has a new fsck_err check,
btree_bitmap_not_marked

- New on disk format version, mi_btree_mitmap, which indicates the new
bitmap is present

- Upgrade table lists the required recovery pass and expected fsck error

- Btree node scan uses the bitmap to skip ranges if we're on the new
version

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: btree node scan: handle encrypted nodes

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: btree_node_scan: Respect member.data_allowed

If a device wasn't used for btree nodes, no need to scan for them.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Don't scan for btree nodes when we can reconstruct

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

bcachefs: Repair pass for scanning for btree nodes

If a btree root or interior btree node goes bad, we're going to lose a
lot of data, unless we can recover the nodes that it pointed to by
scanning.

Fortunately btree node headers are fully self describing, and
additionally the magic number is xored with the filesytem UUID, so we
can do so safely.

This implements the scanning - next patch will rework topology repair to
make use of the found nodes.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>