block: Fix discard alignment calculation and printing

Discard alignment reporting for partitions was incorrect.  Update to
match the algorithm used elsewhere.

The alignment can be negative (misaligned).  Fix format string
accordingly.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

diff --git a/block/genhd.c b/block/genhd.c
index b11a4ad7d571fcfa71a69a2ab8e9cfe5a4d82673..d13ba76a169cfbb1de03f6d5b408a18f73bcb8b9 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -867,7 +867,7 @@ static ssize_t disk_discard_alignment_show(struct device *dev,
 {
        struct gendisk *disk = dev_to_disk(dev);
 
-       return sprintf(buf, "%u\n", queue_discard_alignment(disk->queue));
+       return sprintf(buf, "%d\n", queue_discard_alignment(disk->queue));
 }
 
 static DEVICE_ATTR(range, S_IRUGO, disk_range_show, NULL);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 9b98173a81845bc4dc61b0bb30a516e738c4ec5d..a41bcc8e140fb9daa52451ea5e8e65da3f0ca5a9 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1148,8 +1148,11 @@ static inline int queue_discard_alignment(struct request_queue *q)
 static inline int queue_sector_discard_alignment(struct request_queue *q,
                                                 sector_t sector)
 {
-       return ((sector << 9) - q->limits.discard_alignment)
-               & (q->limits.discard_granularity - 1);
+       struct queue_limits *lim = &q->limits;
+       unsigned int alignment = (sector << 9) & (lim->discard_granularity - 1);
+
+       return (lim->discard_granularity + lim->discard_alignment - alignment)
+               & (lim->discard_granularity - 1);
 }
 
 static inline unsigned int queue_discard_zeroes_data(struct request_queue *q)