block: Update blk_queue_max_sectors and documentation
Clarify blk_queue_max_sectors and update documentation.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 78549c7..605df9b 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -212,26 +212,30 @@
/**
* blk_queue_max_sectors - set max sectors for a request for this queue
* @q: the request queue for the device
- * @max_sectors: max sectors in the usual 512b unit
+ * @max_hw_sectors: max hardware sectors in the usual 512b unit
*
* Description:
- * Enables a low level driver to set an upper limit on the size of
- * received requests.
+ * Enables a low level driver to set a hard upper limit,
+ * max_hw_sectors, on the size of requests. max_hw_sectors is set by
+ * the device driver based upon the combined capabilities of I/O
+ * controller and storage device.
+ *
+ * max_sectors is a soft limit imposed by the block layer for
+ * filesystem type requests. This value can be overridden on a
+ * per-device basis in /sys/block/<device>/queue/max_sectors_kb.
+ * The soft limit can not exceed max_hw_sectors.
**/
-void blk_queue_max_sectors(struct request_queue *q, unsigned int max_sectors)
+void blk_queue_max_sectors(struct request_queue *q, unsigned int max_hw_sectors)
{
- if ((max_sectors << 9) < PAGE_CACHE_SIZE) {
- max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
+ if ((max_hw_sectors << 9) < PAGE_CACHE_SIZE) {
+ max_hw_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
printk(KERN_INFO "%s: set to minimum %d\n",
- __func__, max_sectors);
+ __func__, max_hw_sectors);
}
- if (BLK_DEF_MAX_SECTORS > max_sectors)
- q->limits.max_hw_sectors = q->limits.max_sectors = max_sectors;
- else {
- q->limits.max_sectors = BLK_DEF_MAX_SECTORS;
- q->limits.max_hw_sectors = max_sectors;
- }
+ q->limits.max_hw_sectors = max_hw_sectors;
+ q->limits.max_sectors = min_t(unsigned int, max_hw_sectors,
+ BLK_DEF_MAX_SECTORS);
}
EXPORT_SYMBOL(blk_queue_max_sectors);