Some refactoring - better to explicitly pass stuff around instead of
having it all in the "big bag of state", struct btree_op. Going to prune
struct btree_op quite a bit over time.
Signed-off-by: NKent Overstreet <kmo@daterainc.com>

This was the main point of all this refactoring - now,
btree_insert_check_key() won't fail just because the leaf node happened
to be full.
Signed-off-by: NKent Overstreet <kmo@daterainc.com>

This is prep work for the reworked btree insertion code.

The way we set b->parent is ugly and hacky... the problem is, when
btree_split() or garbage collection splits or rewrites a btree node, the
parent changes for all its (potentially already cached) children.

I may change this later and add some code to look through the btree node
cache and find all our cached child nodes and change the parent pointer
then...
Signed-off-by: NKent Overstreet <kmo@daterainc.com>

Checking i->seq was redundant, because since ages ago we always
initialize the new bset when advancing b->written
Signed-off-by: NKent Overstreet <kmo@daterainc.com>

This code has rotted and it hasn't been used in ages anyways.
Signed-off-by: NKent Overstreet <kmo@daterainc.com>

Now that we're tracking dirty data per stripe, we can add two
optimizations for raid5/6:

 * If a stripe is already dirty, force writes to that stripe to
   writeback mode - to help build up full stripes of dirty data

 * When flushing dirty data, preferentially write out full stripes first
   if there are any.
Signed-off-by: NKent Overstreet <koverstreet@google.com>

Old gcc doesnt like the struct hack, and it is kind of ugly. So finish
off the work to convert pr_debug() statements to tracepoints, and delete
pkey()/pbtree().
Signed-off-by: NKent Overstreet <koverstreet@google.com>

The most significant change is that btree reads are now done
synchronously, instead of asynchronously and doing the post read stuff
from a workqueue.

This was originally done because we can't block on IO under
generic_make_request(). But - we already have a mechanism to punt cache
lookups to workqueue if needed, so if we just use that we don't have to
deal with the complexity of doing things asynchronously.

The main benefit is this makes the locking situation saner; we can hold
our write lock on the btree node until we're finished reading it, and we
don't need that btree_node_read_done() flag anymore.

Also, for writes, btree_write() was broken out into btree_node_write()
and btree_leaf_dirty() - the old code with the boolean argument was dumb
and confusing.

The prio_blocked mechanism was improved a bit too, now the only counter
is in struct btree_write, we don't mess with transfering a count from
struct btree anymore.

This required changing garbage collection to block prios at the start
and unblock when it finishes, which is cleaner than what it was doing
anyways (the old code had mostly the same effect, but was doing it in a
convoluted way)

And the btree iter btree_node_read_done() uses was converted to a real
mempool.
Signed-off-by: NKent Overstreet <koverstreet@google.com>

Does writethrough and writeback caching, handles unclean shutdown, and
has a bunch of other nifty features motivated by real world usage.

See the wiki at http://bcache.evilpiepirate.org for more.
Signed-off-by: NKent Overstreet <koverstreet@google.com>