+static unsigned int lcm(unsigned int a, unsigned int b)
+{
+ if (a && b)
+ return (a * b) / gcd(a, b);
+ else if (b)
+ return b;
+
+ return a;
+}
+
+/**
+ * blk_stack_limits - adjust queue_limits for stacked devices
+ * @t: the stacking driver limits (top)
+ * @b: the underlying queue limits (bottom)
+ * @offset: offset to beginning of data within component device
+ *
+ * Description:
+ * Merges two queue_limit structs. Returns 0 if alignment didn't
+ * change. Returns -1 if adding the bottom device caused
+ * misalignment.
+ */
+int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
+ sector_t offset)
+{
+ sector_t alignment;
+ unsigned int top, bottom, granularity;
+
+ t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
+ t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
+ t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
+
+ t->seg_boundary_mask = min_not_zero(t->seg_boundary_mask,
+ b->seg_boundary_mask);
+
+ t->max_phys_segments = min_not_zero(t->max_phys_segments,
+ b->max_phys_segments);
+
+ t->max_hw_segments = min_not_zero(t->max_hw_segments,
+ b->max_hw_segments);
+
+ t->max_segment_size = min_not_zero(t->max_segment_size,
+ b->max_segment_size);
+
+ granularity = max(b->physical_block_size, b->io_min);
+ alignment = b->alignment_offset - (offset & (granularity - 1));
+
+ if (t->alignment_offset != alignment) {
+
+ top = max(t->physical_block_size, t->io_min)
+ + t->alignment_offset;
+ bottom = granularity + alignment;
+
+ if (max(top, bottom) & (min(top, bottom) - 1))
+ t->misaligned = 1;
+ }
+
+ t->logical_block_size = max(t->logical_block_size,
+ b->logical_block_size);
+
+ t->physical_block_size = max(t->physical_block_size,
+ b->physical_block_size);
+
+ t->io_min = max(t->io_min, b->io_min);
+ t->io_opt = lcm(t->io_opt, b->io_opt);
+
+ t->no_cluster |= b->no_cluster;
+ t->discard_zeroes_data &= b->discard_zeroes_data;
+
+ if (t->physical_block_size & (t->logical_block_size - 1)) {
+ t->physical_block_size = t->logical_block_size;
+ t->misaligned = 1;
+ }
+
+ if (t->io_min & (t->physical_block_size - 1)) {
+ t->io_min = t->physical_block_size;
+ t->misaligned = 1;
+ }
+
+ if (t->io_opt & (t->physical_block_size - 1)) {
+ t->io_opt = 0;
+ t->misaligned = 1;
+ }
+
+ t->alignment_offset = lcm(t->alignment_offset, alignment)
+ & (max(t->physical_block_size, t->io_min) - 1);
+
+ if (t->alignment_offset & (t->logical_block_size - 1))
+ t->misaligned = 1;
+
+ /* Discard alignment and granularity */
+ if (b->discard_granularity) {
+
+ alignment = b->discard_alignment -
+ (offset & (b->discard_granularity - 1));
+
+ if (t->discard_granularity != 0 &&
+ t->discard_alignment != alignment) {
+ top = t->discard_granularity + t->discard_alignment;
+ bottom = b->discard_granularity + alignment;
+
+ /* Verify that top and bottom intervals line up */
+ if (max(top, bottom) & (min(top, bottom) - 1))
+ t->discard_misaligned = 1;
+ }
+
+ t->discard_granularity = max(t->discard_granularity,
+ b->discard_granularity);
+ t->discard_alignment = lcm(t->discard_alignment, alignment) &
+ (t->discard_granularity - 1);
+ }
+
+ return t->misaligned ? -1 : 0;
+}
+EXPORT_SYMBOL(blk_stack_limits);
+
+/**
+ * disk_stack_limits - adjust queue limits for stacked drivers
+ * @disk: MD/DM gendisk (top)
+ * @bdev: the underlying block device (bottom)
+ * @offset: offset to beginning of data within component device
+ *
+ * Description:
+ * Merges the limits for two queues. Returns 0 if alignment
+ * didn't change. Returns -1 if adding the bottom device caused
+ * misalignment.
+ */
+void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
+ sector_t offset)
+{
+ struct request_queue *t = disk->queue;
+ struct request_queue *b = bdev_get_queue(bdev);
+
+ offset += get_start_sect(bdev) << 9;
+
+ if (blk_stack_limits(&t->limits, &b->limits, offset) < 0) {
+ char top[BDEVNAME_SIZE], bottom[BDEVNAME_SIZE];
+
+ disk_name(disk, 0, top);
+ bdevname(bdev, bottom);
+
+ printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
+ top, bottom);
+ }
+
+ if (!t->queue_lock)
+ WARN_ON_ONCE(1);
+ else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
+ unsigned long flags;
+
+ spin_lock_irqsave(t->queue_lock, flags);
+ if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags))
+ queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
+ spin_unlock_irqrestore(t->queue_lock, flags);
+ }
+}
+EXPORT_SYMBOL(disk_stack_limits);
+