Function vdev_mirror_map_init

freebsd/contrib/openzfs/module/zfs/vdev_mirror.c:263–385

* Avoid inlining the function to keep vdev_mirror_io_start(), which * is this functions only caller, as small as possible on the stack. */

 * is this functions only caller, as small as possible on the stack.
 */
noinline static mirror_map_t *
vdev_mirror_map_init(zio_t *zio)
{
	mirror_map_t *mm = NULL;
	mirror_child_t *mc;
	vdev_t *vd = zio->io_vd;
	int c;

	if (vd == NULL) {
		dva_t *dva = zio->io_bp->blk_dva;
		spa_t *spa = zio->io_spa;
		dsl_scan_t *scn = spa->spa_dsl_pool->dp_scan;
		dva_t dva_copy[SPA_DVAS_PER_BP];

		/*
		 * The sequential scrub code sorts and issues all DVAs
		 * of a bp separately. Each of these IOs includes all
		 * original DVA copies so that repairs can be performed
		 * in the event of an error, but we only actually want
		 * to check the first DVA since the others will be
		 * checked by their respective sorted IOs. Only if we
		 * hit an error will we try all DVAs upon retrying.
		 *
		 * Note: This check is safe even if the user switches
		 * from a legacy scrub to a sequential one in the middle
		 * of processing, since scn_is_sorted isn't updated until
		 * all outstanding IOs from the previous scrub pass
		 * complete.
		 */
		if ((zio->io_flags & ZIO_FLAG_SCRUB) &&
		    !(zio->io_flags & ZIO_FLAG_IO_RETRY) &&
		    dsl_scan_scrubbing(spa->spa_dsl_pool) &&
		    scn->scn_is_sorted) {
			c = 1;
		} else {
			c = BP_GET_NDVAS(zio->io_bp);
		}

		/*
		 * If the pool cannot be written to, then infer that some
		 * DVAs might be invalid or point to vdevs that do not exist.
		 * We skip them.
		 */
		if (!spa_writeable(spa)) {
			ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);
			int j = 0;
			for (int i = 0; i < c; i++) {
				if (zfs_dva_valid(spa, &dva[i], zio->io_bp))
					dva_copy[j++] = dva[i];
			}
			if (j == 0) {
				zio->io_vsd = NULL;
				zio->io_error = ENXIO;
				return (NULL);
			}
			if (j < c) {
				dva = dva_copy;
				c = j;