metaslab_alloc
int metaslab_alloc(spa_t *, metaslab_class_t *, uint64_t,
error = metaslab_alloc(spa, mc, SPA_GANGBLOCKSIZE,
error = metaslab_alloc(spa, mc, zio->io_size, bp,
error = metaslab_alloc(spa, mc, zio->io_size, bp,
error = metaslab_alloc(spa, spa_log_class(spa), size, new_bp, 1,
error = metaslab_alloc(spa, spa_normal_class(spa), size,