bcachefs: Allocator now copes with unaligned buckets

We had a buggy release of bcachefs-tools that wasn't properly aligning
bucket sizes.

We can't ask users to reformat - and it's easy to teach the allocator to
make sure writes are properly aligned.

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

Author: Kent Overstreet

fs/bcachefs/alloc_foreground.c

@@ -1425,6 +1425,8 @@ int bch2_alloc_sectors_start_trans(struct btree_trans *trans,
 	open_bucket_for_each(c, &wp->ptrs, ob, i)
 		wp->sectors_free = min(wp->sectors_free, ob->sectors_free);
 
+	wp->sectors_free = rounddown(wp->sectors_free, block_sectors(c));
+
 	BUG_ON(!wp->sectors_free || wp->sectors_free == UINT_MAX);
 
 	return 0;

fs/bcachefs/alloc_foreground.h

@@ -110,7 +110,9 @@ static inline void bch2_alloc_sectors_done_inlined(struct bch_fs *c, struct writ
 	unsigned i;
 
 	open_bucket_for_each(c, &wp->ptrs, ob, i)
-		ob_push(c, !ob->sectors_free ? &ptrs : &keep, ob);
+		ob_push(c, ob->sectors_free < block_sectors(c)
+			? &ptrs
+			: &keep, ob);
 	wp->ptrs = keep;
 
 	mutex_unlock(&wp->lock);