bcache: Clean up cache_lookup_fn

There was some looping in submit_partial_cache_hit() and
submit_partial_cache_hit() that isn't needed anymore - originally, we
wouldn't necessarily process the full hit or miss all at once because
when splitting the bio, we took into account the restrictions of the
device we were sending it to.

But, device bio size restrictions are now handled elsewhere, with a
wrapper around generic_make_request() - so that looping has been
unnecessary for awhile now and we can now do quite a bit of cleanup.

And if we trim the key we're reading from to match the subset we're
actually reading, we don't have to explicitly calculate bi_sector
anymore. Neat.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/request.c

@@ -663,86 +663,70 @@ static void bch_cache_read_endio(struct bio *bio, int error)
 	bch_bbio_endio(s->op.c, bio, error, "reading from cache");
 }
 
-static int submit_partial_cache_miss(struct btree *b, struct search *s,
-				     struct bkey *k)
-{
-	struct bio *bio = &s->bio.bio;
-	int ret = MAP_CONTINUE;
-
-	do {
-		unsigned sectors = INT_MAX;
-
-		if (KEY_INODE(k) == s->op.inode) {
-			if (KEY_START(k) <= bio->bi_sector)
-				break;
-
-			sectors = min_t(uint64_t, sectors,
-					KEY_START(k) - bio->bi_sector);
-		}
-
-		ret = s->d->cache_miss(b, s, bio, sectors);
-	} while (ret == MAP_CONTINUE);
-
-	return ret;
-}
-
 /*
  * Read from a single key, handling the initial cache miss if the key starts in
  * the middle of the bio
  */
-static int submit_partial_cache_hit(struct btree_op *op, struct btree *b,
-				    struct bkey *k)
+static int cache_lookup_fn(struct btree_op *op, struct btree *b, struct bkey *k)
 {
 	struct search *s = container_of(op, struct search, op);
-	struct bio *bio = &s->bio.bio;
+	struct bio *n, *bio = &s->bio.bio;
+	struct bkey *bio_key;
 	unsigned ptr;
-	struct bio *n;
 
-	int ret = submit_partial_cache_miss(b, s, k);
-	if (ret != MAP_CONTINUE || !KEY_SIZE(k))
-		return ret;
+	if (bkey_cmp(k, &KEY(op->inode, bio->bi_sector, 0)) <= 0)
+		return MAP_CONTINUE;
+
+	if (KEY_INODE(k) != s->op.inode ||
+	    KEY_START(k) > bio->bi_sector) {
+		unsigned bio_sectors = bio_sectors(bio);
+		unsigned sectors = KEY_INODE(k) == s->op.inode
+			? min_t(uint64_t, INT_MAX,
+				KEY_START(k) - bio->bi_sector)
+			: INT_MAX;
+
+		int ret = s->d->cache_miss(b, s, bio, sectors);
+		if (ret != MAP_CONTINUE)
+			return ret;
+
+		/* if this was a complete miss we shouldn't get here */
+		BUG_ON(bio_sectors <= sectors);
+	}
+
+	if (!KEY_SIZE(k))
+		return MAP_CONTINUE;
 
 	/* XXX: figure out best pointer - for multiple cache devices */
 	ptr = 0;
 
 	PTR_BUCKET(b->c, k, ptr)->prio = INITIAL_PRIO;
 
-	while (ret == MAP_CONTINUE &&
-	       KEY_INODE(k) == op->inode &&
-	       bio->bi_sector < KEY_OFFSET(k)) {
-		struct bkey *bio_key;
-		sector_t sector = PTR_OFFSET(k, ptr) +
-			(bio->bi_sector - KEY_START(k));
-		unsigned sectors = min_t(uint64_t, INT_MAX,
-					 KEY_OFFSET(k) - bio->bi_sector);
-
-		n = bch_bio_split(bio, sectors, GFP_NOIO, s->d->bio_split);
-		if (n == bio)
-			ret = MAP_DONE;
-
-		bio_key = &container_of(n, struct bbio, bio)->key;
+	n = bch_bio_split(bio, min_t(uint64_t, INT_MAX,
+				     KEY_OFFSET(k) - bio->bi_sector),
+			  GFP_NOIO, s->d->bio_split);
 
-		/*
-		 * The bucket we're reading from might be reused while our bio
-		 * is in flight, and we could then end up reading the wrong
-		 * data.
-		 *
-		 * We guard against this by checking (in cache_read_endio()) if
-		 * the pointer is stale again; if so, we treat it as an error
-		 * and reread from the backing device (but we don't pass that
-		 * error up anywhere).
-		 */
+	bio_key = &container_of(n, struct bbio, bio)->key;
+	bch_bkey_copy_single_ptr(bio_key, k, ptr);
 
-		bch_bkey_copy_single_ptr(bio_key, k, ptr);
-		SET_PTR_OFFSET(bio_key, 0, sector);
+	bch_cut_front(&KEY(s->op.inode, n->bi_sector, 0), bio_key);
+	bch_cut_back(&KEY(s->op.inode, bio_end_sector(n), 0), bio_key);
 
-		n->bi_end_io	= bch_cache_read_endio;
-		n->bi_private	= &s->cl;
+	n->bi_end_io	= bch_cache_read_endio;
+	n->bi_private	= &s->cl;
 
-		__bch_submit_bbio(n, b->c);
-	}
+	/*
+	 * The bucket we're reading from might be reused while our bio
+	 * is in flight, and we could then end up reading the wrong
+	 * data.
+	 *
+	 * We guard against this by checking (in cache_read_endio()) if
+	 * the pointer is stale again; if so, we treat it as an error
+	 * and reread from the backing device (but we don't pass that
+	 * error up anywhere).
+	 */
 
-	return ret;
+	__bch_submit_bbio(n, b->c);
+	return n == bio ? MAP_DONE : MAP_CONTINUE;
 }
 
 static void cache_lookup(struct closure *cl)
@@ -753,7 +737,7 @@ static void cache_lookup(struct closure *cl)
 
 	int ret = bch_btree_map_keys(op, op->c,
 				     &KEY(op->inode, bio->bi_sector, 0),
-				     submit_partial_cache_hit, 1);
+				     cache_lookup_fn, MAP_END_KEY);
 	if (ret == -EAGAIN)
 		continue_at(cl, cache_lookup, bcache_wq);