btrfs: add secure erase mode to CLEAR_FREE ioctl

Add another type of clearing that will do secure erase on the unused
space.

This requires hardware support and works as a regular discard while also
deleting any copied or cached blocks. Same as "blkdiscard --secure".

The unused space ranges may not be aligned to the secure erase block or
be of a sufficient length, the exact result depends on the device.
Some blocks may still contain valid data even after this ioctl.

Signed-off-by: David Sterba <[email protected]>

Author: kdave

fs/btrfs/extent-tree.c

@@ -1253,6 +1253,9 @@ static int btrfs_issue_clear_op(struct block_device *bdev, u64 start, u64 size,
 	unsigned int flags = BLKDEV_ZERO_KILLABLE;
 
 	switch (clear) {
+	case BTRFS_CLEAR_OP_SECURE_ERASE:
+		return blkdev_issue_secure_erase(bdev, start >> SECTOR_SHIFT,
+						 size >> SECTOR_SHIFT, GFP_NOFS);
 	case BTRFS_CLEAR_OP_DISCARD:
 		return blkdev_issue_discard(bdev, start >> SECTOR_SHIFT,
 					    size >> SECTOR_SHIFT, GFP_NOFS);

include/uapi/linux/btrfs.h

@@ -1107,6 +1107,13 @@ enum btrfs_clear_op_type {
 	 * (Same as blkdev_issue_zeroout() with 0 flags).
 	 */
 	BTRFS_CLEAR_OP_ZERO,
+	/*
+	 * Do a secure erase operation on the range. If supported by the
+	 * underlying hardware, this works as regular discard except that all
+	 * copies of the discarded blocks that were possibly created by
+	 * garbage collection must also be erased.
+	 */
+	BTRFS_CLEAR_OP_SECURE_ERASE,
 	BTRFS_NR_CLEAR_OP_TYPES,
 };