block: Allow devices to indicate whether discarded blocks are zeroed
The discard ioctl is used by mkfs utilities to clear a block device
prior to putting metadata down. However, not all devices return zeroed
blocks after a discard. Some drives return stale data, potentially
containing old superblocks. It is therefore important to know whether
discarded blocks are properly zeroed.
Both ATA and SCSI drives have configuration bits that indicate whether
zeroes are returned after a discard operation. Implement a block level
interface that allows this information to be bubbled up the stack and
queried via a new block device ioctl.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e727f6c..784a919 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -322,6 +322,7 @@
unsigned char misaligned;
unsigned char discard_misaligned;
unsigned char no_cluster;
+ signed char discard_zeroes_data;
};
struct request_queue
@@ -1150,6 +1151,19 @@
& (q->limits.discard_granularity - 1);
}
+static inline unsigned int queue_discard_zeroes_data(struct request_queue *q)
+{
+ if (q->limits.discard_zeroes_data == 1)
+ return 1;
+
+ return 0;
+}
+
+static inline unsigned int bdev_discard_zeroes_data(struct block_device *bdev)
+{
+ return queue_discard_zeroes_data(bdev_get_queue(bdev));
+}
+
static inline int queue_dma_alignment(struct request_queue *q)
{
return q ? q->dma_alignment : 511;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 79cea80..891f7d6 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -304,6 +304,7 @@
#define BLKIOOPT _IO(0x12,121)
#define BLKALIGNOFF _IO(0x12,122)
#define BLKPBSZGET _IO(0x12,123)
+#define BLKDISCARDZEROES _IO(0x12,124)
#define BMAP_IOCTL 1 /* obsolete - kept for compatibility */
#define FIBMAP _IO(0x00,1) /* bmap access */