[PATCH v2 2/4] block: factor block size and alignment handling out of blk_stack_limits

[Yao Sang]

Topology limits are the block size and alignment limits that the top
device exposes after its data is placed at an offset on a bottom device.
blk_stack_limits() uses start, the first data sector in the bottom device
used by the top device, to calculate alignment_offset.

It then stacks logical_block_size, physical_block_size, io_min, io_opt and
chunk_sectors, checks that they are compatible, and rounds max_sectors,
max_hw_sectors and max_dev_sectors down to the final logical_block_size.

Keep these operations together because the checks and rounding must run
after the final logical and physical block sizes are known. Factor them
into a static blk_stack_topology_limits() helper.

There is no behavior change.

Signed-off-by: Yao Sang <sangyao at kylinos.cn>
---
 block/blk-settings.c | 169 ++++++++++++++++++++++++-------------------
 1 file changed, 93 insertions(+), 76 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 8274631290db..1aff818aaaac 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -756,6 +756,96 @@ static void blk_stack_atomic_writes_limits(struct queue_limits *t,
 	t->atomic_write_hw_boundary = 0;
 }
 
+/*
+ * Stack and check logical_block_size, physical_block_size, io_min, io_opt,
+ * chunk_sectors and alignment_offset for a bottom-device range, then round
+ * max_sectors, max_hw_sectors and max_dev_sectors to logical_block_size.
+ */
+static int blk_stack_topology_limits(struct queue_limits *t,
+		const struct queue_limits *b, sector_t start)
+{
+	unsigned int top, bottom, alignment;
+	int ret = 0;
+
+	t->flags |= b->flags & BLK_FLAG_MISALIGNED;
+
+	alignment = queue_limit_alignment_offset(b, start);
+
+	/*
+	 * The bottom device has a different alignment. Check that it is
+	 * compatible with the current top alignment.
+	 */
+	if (t->alignment_offset != alignment) {
+		top = max(t->physical_block_size, t->io_min) +
+			t->alignment_offset;
+		bottom = max(b->physical_block_size, b->io_min) + alignment;
+
+		/* Verify that top and bottom intervals line up. */
+		if (max(top, bottom) % min(top, bottom)) {
+			t->flags |= BLK_FLAG_MISALIGNED;
+			ret = -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_not_zero(t->io_opt, b->io_opt);
+
+	/* Set non-power-of-2 compatible chunk_sectors boundary. */
+	if (b->chunk_sectors)
+		t->chunk_sectors = gcd(t->chunk_sectors, b->chunk_sectors);
+
+	/* Physical block size a multiple of the logical block size? */
+	if (t->physical_block_size & (t->logical_block_size - 1)) {
+		t->physical_block_size = t->logical_block_size;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	/* Minimum I/O a multiple of the physical block size? */
+	if (t->io_min & (t->physical_block_size - 1)) {
+		t->io_min = t->physical_block_size;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	/* Optimal I/O a multiple of the physical block size? */
+	if (t->io_opt & (t->physical_block_size - 1)) {
+		t->io_opt = 0;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	/* chunk_sectors a multiple of the physical block size? */
+	if (t->chunk_sectors % (t->physical_block_size >> SECTOR_SHIFT)) {
+		t->chunk_sectors = 0;
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	/* Find lowest common alignment_offset. */
+	t->alignment_offset = lcm_not_zero(t->alignment_offset, alignment) %
+		max(t->physical_block_size, t->io_min);
+
+	/* Verify that new alignment_offset is on a logical block boundary. */
+	if (t->alignment_offset & (t->logical_block_size - 1)) {
+		t->flags |= BLK_FLAG_MISALIGNED;
+		ret = -1;
+	}
+
+	t->max_sectors = blk_round_down_sectors(t->max_sectors,
+						t->logical_block_size);
+	t->max_hw_sectors = blk_round_down_sectors(t->max_hw_sectors,
+						   t->logical_block_size);
+	t->max_dev_sectors = blk_round_down_sectors(t->max_dev_sectors,
+						    t->logical_block_size);
+
+	return ret;
+}
+
 /**
  * blk_stack_limits - adjust queue_limits for stacked devices
  * @t:	the stacking driver limits (top device)
@@ -780,8 +870,8 @@ static void blk_stack_atomic_writes_limits(struct queue_limits *t,
 int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 		     sector_t start)
 {
-	unsigned int top, bottom, alignment;
-	int ret = 0;
+	unsigned int alignment;
+	int ret;
 
 	t->features |= (b->features & BLK_FEAT_INHERIT_MASK);
 
@@ -798,8 +888,6 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 	if (!(b->features & BLK_FEAT_PCI_P2PDMA))
 		t->features &= ~BLK_FEAT_PCI_P2PDMA;
 
-	t->flags |= (b->flags & BLK_FLAG_MISALIGNED);
-
 	t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
 	t->max_user_sectors = min_not_zero(t->max_user_sectors,
 			b->max_user_sectors);
@@ -830,80 +918,9 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
 
 	t->max_segment_size = min_not_zero(t->max_segment_size,
 					   b->max_segment_size);
-
-	alignment = queue_limit_alignment_offset(b, start);
-
-	/* Bottom device has different alignment.  Check that it is
-	 * compatible with the current top alignment.
-	 */
-	if (t->alignment_offset != alignment) {
-
-		top = max(t->physical_block_size, t->io_min)
-			+ t->alignment_offset;
-		bottom = max(b->physical_block_size, b->io_min) + alignment;
-
-		/* Verify that top and bottom intervals line up */
-		if (max(top, bottom) % min(top, bottom)) {
-			t->flags |= BLK_FLAG_MISALIGNED;
-			ret = -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_not_zero(t->io_opt, b->io_opt);
 	t->dma_alignment = max(t->dma_alignment, b->dma_alignment);
 
-	/* Set non-power-of-2 compatible chunk_sectors boundary */
-	if (b->chunk_sectors)
-		t->chunk_sectors = gcd(t->chunk_sectors, b->chunk_sectors);
-
-	/* Physical block size a multiple of the logical block size? */
-	if (t->physical_block_size & (t->logical_block_size - 1)) {
-		t->physical_block_size = t->logical_block_size;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	/* Minimum I/O a multiple of the physical block size? */
-	if (t->io_min & (t->physical_block_size - 1)) {
-		t->io_min = t->physical_block_size;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	/* Optimal I/O a multiple of the physical block size? */
-	if (t->io_opt & (t->physical_block_size - 1)) {
-		t->io_opt = 0;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	/* chunk_sectors a multiple of the physical block size? */
-	if (t->chunk_sectors % (t->physical_block_size >> SECTOR_SHIFT)) {
-		t->chunk_sectors = 0;
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	/* Find lowest common alignment_offset */
-	t->alignment_offset = lcm_not_zero(t->alignment_offset, alignment)
-		% max(t->physical_block_size, t->io_min);
-
-	/* Verify that new alignment_offset is on a logical block boundary */
-	if (t->alignment_offset & (t->logical_block_size - 1)) {
-		t->flags |= BLK_FLAG_MISALIGNED;
-		ret = -1;
-	}
-
-	t->max_sectors = blk_round_down_sectors(t->max_sectors, t->logical_block_size);
-	t->max_hw_sectors = blk_round_down_sectors(t->max_hw_sectors, t->logical_block_size);
-	t->max_dev_sectors = blk_round_down_sectors(t->max_dev_sectors, t->logical_block_size);
+	ret = blk_stack_topology_limits(t, b, start);
 
 	/* Discard alignment and granularity */
 	if (b->discard_granularity) {
-- 
2.25.1