static int rd_build_device_space(struct rd_dev *rd_dev)
{
	u32 i = 0, j, page_offset = 0, sg_per_table, sg_tables, total_sg_needed;
	u32 max_sg_per_table = (RD_MAX_ALLOCATION_SIZE /
				sizeof(struct scatterlist));
	struct rd_dev_sg_table *sg_table;
	struct page *pg;
	struct scatterlist *sg;

	if (rd_dev->rd_page_count <= 0) {
		pr_err("Illegal page count: %u for Ramdisk device\n",
			rd_dev->rd_page_count);
		return -EINVAL;
	}

	/* Don't need backing pages for NULLIO */
	if (rd_dev->rd_flags & RDF_NULLIO)
		return 0;

	total_sg_needed = rd_dev->rd_page_count;

	sg_tables = (total_sg_needed / max_sg_per_table) + 1;

	sg_table = kzalloc(sg_tables * sizeof(struct rd_dev_sg_table), GFP_KERNEL);
	if (!sg_table) {
		pr_err("Unable to allocate memory for Ramdisk"
			" scatterlist tables\n");
		return -ENOMEM;
	}

	rd_dev->sg_table_array = sg_table;
	rd_dev->sg_table_count = sg_tables;

	while (total_sg_needed) {
		sg_per_table = (total_sg_needed > max_sg_per_table) ?
			max_sg_per_table : total_sg_needed;

		sg = kzalloc(sg_per_table * sizeof(struct scatterlist),
				GFP_KERNEL);
		if (!sg) {
			pr_err("Unable to allocate scatterlist array"
				" for struct rd_dev\n");
			return -ENOMEM;
		}

		sg_init_table(sg, sg_per_table);

		sg_table[i].sg_table = sg;
		sg_table[i].rd_sg_count = sg_per_table;
		sg_table[i].page_start_offset = page_offset;
		sg_table[i++].page_end_offset = (page_offset + sg_per_table)
						- 1;

		for (j = 0; j < sg_per_table; j++) {
			pg = alloc_pages(GFP_KERNEL, 0);
			if (!pg) {
				pr_err("Unable to allocate scatterlist"
					" pages for struct rd_dev_sg_table\n");
				return -ENOMEM;
			}
			sg_assign_page(&sg[j], pg);
			sg[j].length = PAGE_SIZE;
		}

		page_offset += sg_per_table;
		total_sg_needed -= sg_per_table;
	}

	pr_debug("CORE_RD[%u] - Built Ramdisk Device ID: %u space of"
		" %u pages in %u tables\n", rd_dev->rd_host->rd_host_id,
		rd_dev->rd_dev_id, rd_dev->rd_page_count,
		rd_dev->sg_table_count);

	return 0;
}
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