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block: Allow devices to indicate whether discarded blocks are zeroed

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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 <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Martin K. Petersen 2009-12-03 09:24:48 +01:00 • committed by Jens Axboe
commit 98262f2762
6 changed files with 32 additions and 0 deletions
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block/ioctl.c
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@ -280,6 +280,8 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
return put_uint(arg, bdev_io_opt(bdev));
case BLKALIGNOFF:
return put_int(arg, bdev_alignment_offset(bdev));
case BLKDISCARDZEROES:
return put_uint(arg, bdev_discard_zeroes_data(bdev));
case BLKSECTGET:
return put_ushort(arg, queue_max_sectors(bdev_get_queue(bdev)));
case BLKRASET: