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 b11a4ad..d13ba76 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 9b98173..a41bcc8 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)