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/block/compat_ioctl.c b/block/compat_ioctl.c
index 9bd086c..4eb8e9e 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c
@@ -747,6 +747,8 @@
return compat_put_uint(arg, bdev_io_opt(bdev));
case BLKALIGNOFF:
return compat_put_int(arg, bdev_alignment_offset(bdev));
+ case BLKDISCARDZEROES:
+ return compat_put_uint(arg, bdev_discard_zeroes_data(bdev));
case BLKFLSBUF:
case BLKROSET:
case BLKDISCARD: