Add a tracepoint for any time we return an error and unwind.

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

The new guard(), scoped_guard() allow for more natural code.

Some of the uses with creative flow control have been left.

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

Fast device removal, that uses backpointers to find pointers to the
device being removed instead of a full metadata scan.

This requires BCH_SB_MEMBER_DELETED_UUID, which is an incompatible
change - hence the version number bump. We don't fully trust
backpointers, so we don't want to reuse device indexes until after a
fsck has verified that there aren't any pointers to removed devices.

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

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

Convert device IO refs to enumerated_refs, for easier debugging of
refcount issues.

Simple conversion: enumerate all users and convert to the new helpers.

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

Drop the single-purpose write ref code in bcachefs.h, and convert to
enumarated refs.

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

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

More stack usage improvements: instead of creating a new alloc_request
(currently on the stack), save/restore just the fields we need to reuse.

This is a bit tricky, because we're doing a normal alloc_foreground.c
allocation, which calls into ec.c to get a stripe, which then does more
normal allocations - some of the fields get reused, and used
differently.

So we have to save and restore them - but the stack usage improvements
will be well worth it.

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

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

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