[PATCH v2 2/8] block: Support configuring limits below the page size

[Bart Van Assche <bvanassche@acm.org>]

Allow block drivers to configure the following if
CONFIG_BLK_SUB_PAGE_SEGMENTS=y:
* Maximum number of hardware sectors values smaller than
  PAGE_SIZE >> SECTOR_SHIFT. With PAGE_SIZE = 4096 this means that values
  below 8 become supported.
* A maximum segment size smaller than the page size. This is most useful
  for page sizes above 4096 bytes.

The behavior of the block layer is not modified if
CONFIG_BLK_SUB_PAGE_SEGMENTS=n.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Keith Busch <kbusch@kernel.org>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/blk-settings.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 0477c4d527fe..f9d78dea0291 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -122,12 +122,14 @@ EXPORT_SYMBOL(blk_queue_bounce_limit);
 void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_sectors)
 {
 	struct queue_limits *limits = &q->limits;
+	unsigned int min_max_hw_sectors = blk_queue_sub_page_segments(q) ? 1 :
+		PAGE_SIZE >> SECTOR_SHIFT;
 	unsigned int max_sectors;
 
-	if ((max_hw_sectors << 9) < PAGE_SIZE) {
-		max_hw_sectors = 1 << (PAGE_SHIFT - 9);
-		printk(KERN_INFO "%s: set to minimum %d\n",
-		       __func__, max_hw_sectors);
+	if (max_hw_sectors < min_max_hw_sectors) {
+		max_hw_sectors = min_max_hw_sectors;
+		printk(KERN_INFO "%s: set to minimum %u\n", __func__,
+		       max_hw_sectors);
 	}
 
 	max_hw_sectors = round_down(max_hw_sectors,
@@ -277,10 +279,12 @@ EXPORT_SYMBOL_GPL(blk_queue_max_discard_segments);
  **/
 void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
 {
-	if (max_size < PAGE_SIZE) {
-		max_size = PAGE_SIZE;
-		printk(KERN_INFO "%s: set to minimum %d\n",
-		       __func__, max_size);
+	unsigned int min_max_segment_size = blk_queue_sub_page_segments(q) ?
+		SECTOR_SIZE : PAGE_SIZE;
+
+	if (max_size < min_max_segment_size) {
+		max_size = min_max_segment_size;
+		printk(KERN_INFO "%s: set to minimum %u\n", __func__, max_size);
 	}
 
 	/* see blk_queue_virt_boundary() for the explanation */