extern int metaslab_alloc(spa_t *spa, metaslab_class_t *mc, uint64_t psize,
blkptr_t *bp, int ncopies, uint64_t txg, blkptr_t *hintbp, int flags);
extern int metaslab_alloc(spa_t *spa, metaslab_class_t *mc, uint64_t psize,
blkptr_t *bp, int ncopies, uint64_t txg, blkptr_t *hintbp, int flags);