[dm-devel] [PATCH v2 4/4] brd: implement secure erase and write zeroes

[Mikulas Patocka]

This patch implements REQ_OP_SECURE_ERASE and REQ_OP_WRITE_ZEROES on brd.
Write zeroes will free the pages just like discard, but the difference is
that it writes zeroes to the preceding and following page if the range is
not aligned on page boundary. Secure erase is just like write zeroes,
except that it clears the page content before freeing the page.

Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>

---
 drivers/block/brd.c |   30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

Index: linux-2.6/drivers/block/brd.c
===================================================================
--- linux-2.6.orig/drivers/block/brd.c
+++ linux-2.6/drivers/block/brd.c
@@ -115,7 +115,7 @@ static void brd_free_page_rcu(struct rcu
 	__free_page(page);
 }
 
-static void brd_free_page(struct brd_device *brd, sector_t sector)
+static void brd_free_page(struct brd_device *brd, sector_t sector, bool secure)
 {
 	struct page *page;
 	pgoff_t idx;
@@ -124,8 +124,11 @@ static void brd_free_page(struct brd_dev
 	idx = sector >> PAGE_SECTORS_SHIFT;
 	page = radix_tree_delete(&brd->brd_pages, idx);
 	spin_unlock(&brd->brd_lock);
-	if (page)
+	if (page) {
+		if (secure)
+			clear_highpage(page);
 		call_rcu(&page->rcu_head, brd_free_page_rcu);
+	}
 }
 
 /*
@@ -300,23 +303,34 @@ out:
 
 void brd_do_discard(struct brd_device *brd, struct bio *bio)
 {
-	sector_t sector, len, front_pad;
+	bool zero_padding;
+	sector_t sector, len, front_pad, end_pad;
 
 	if (unlikely(!discard)) {
 		bio->bi_status = BLK_STS_NOTSUPP;
 		return;
 	}
 
+	zero_padding = bio_op(bio) == REQ_OP_SECURE_ERASE || bio_op(bio) == REQ_OP_WRITE_ZEROES;
 	sector = bio->bi_iter.bi_sector;
 	len = bio_sectors(bio);
 	front_pad = -sector & (PAGE_SECTORS - 1);
+
+	if (zero_padding && unlikely(front_pad != 0))
+		copy_to_brd(brd, page_address(ZERO_PAGE(0)), sector, min(len, front_pad) << SECTOR_SHIFT);
+
 	sector += front_pad;
 	if (unlikely(len <= front_pad))
 		return;
 	len -= front_pad;
-	len = round_down(len, PAGE_SECTORS);
+
+	end_pad = len & (PAGE_SECTORS - 1);
+	if (zero_padding && unlikely(end_pad != 0))
+		copy_to_brd(brd, page_address(ZERO_PAGE(0)), sector + len - end_pad, end_pad << SECTOR_SHIFT);
+	len -= end_pad;
+
 	while (len) {
-		brd_free_page(brd, sector);
+		brd_free_page(brd, sector, bio_op(bio) == REQ_OP_SECURE_ERASE);
 		sector += PAGE_SECTORS;
 		len -= PAGE_SECTORS;
 		cond_resched();
@@ -330,7 +344,9 @@ static void brd_submit_bio(struct bio *b
 	struct bio_vec bvec;
 	struct bvec_iter iter;
 
-	if (bio_op(bio) == REQ_OP_DISCARD) {
+	if (bio_op(bio) == REQ_OP_DISCARD ||
+	    bio_op(bio) == REQ_OP_SECURE_ERASE ||
+	    bio_op(bio) == REQ_OP_WRITE_ZEROES) {
 		brd_do_discard(brd, bio);
 		goto endio;
 	}
@@ -464,6 +480,8 @@ static int brd_alloc(int i)
 	if (discard) {
 		disk->queue->limits.discard_granularity = PAGE_SIZE;
 		blk_queue_max_discard_sectors(disk->queue, UINT_MAX);
+		blk_queue_max_write_zeroes_sectors(disk->queue, UINT_MAX);
+		blk_queue_max_secure_erase_sectors(disk->queue, UINT_MAX);
 	}
 
 	/* Tell the block layer that this is not a rotational device */