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Commit b7c33571 authored by Nick Piggin's avatar Nick Piggin Committed by Jens Axboe
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brd: support discard 



Support discard requests in brd by zeroing or deleting the underlying backing
pages. This is simply to help with testing and documentation nature of
brd code.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 0e3c9a22

drivers/block/brd.c

+52 −1
Original line number Diff line number Diff line
@@ -133,6 +133,28 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector) 
	return page;

}



static void brd_free_page(struct brd_device *brd, sector_t sector)

{

	struct page *page;

	pgoff_t idx;



	spin_lock(&brd->brd_lock);

	idx = sector >> PAGE_SECTORS_SHIFT;

	page = radix_tree_delete(&brd->brd_pages, idx);

	spin_unlock(&brd->brd_lock);

	if (page)

		__free_page(page);

}



static void brd_zero_page(struct brd_device *brd, sector_t sector)

{

	struct page *page;



	page = brd_lookup_page(brd, sector);

	if (page)

		clear_highpage(page);

}



/*

 * Free all backing store pages and radix tree. This must only be called when

 * there are no other users of the device.
@@ -189,6 +211,24 @@ static int copy_to_brd_setup(struct brd_device *brd, sector_t sector, size_t n) 
	return 0;

}



static void discard_from_brd(struct brd_device *brd,

			sector_t sector, size_t n)

{

	while (n >= PAGE_SIZE) {

		/*

		 * Don't want to actually discard pages here because

		 * re-allocating the pages can result in writeback

		 * deadlocks under heavy load.

		 */

		if (0)

			brd_free_page(brd, sector);

		else

			brd_zero_page(brd, sector);

		sector += PAGE_SIZE >> SECTOR_SHIFT;

		n -= PAGE_SIZE;

	}

}



/*

 * Copy n bytes from src to the brd starting at sector. Does not sleep.

 */
@@ -300,6 +340,12 @@ static int brd_make_request(struct request_queue *q, struct bio *bio) 
						get_capacity(bdev->bd_disk))

		goto out;



	if (unlikely(bio_rw_flagged(bio, BIO_RW_DISCARD))) {

		err = 0;

		discard_from_brd(brd, sector, bio->bi_size);

		goto out;

	}



	rw = bio_rw(bio);

	if (rw == READA)

		rw = READ;
@@ -437,6 +483,11 @@ static struct brd_device *brd_alloc(int i) 
	blk_queue_max_hw_sectors(brd->brd_queue, 1024);

	blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY);



	brd->brd_queue->limits.discard_granularity = PAGE_SIZE;

	brd->brd_queue->limits.max_discard_sectors = UINT_MAX;

	brd->brd_queue->limits.discard_zeroes_data = 1;

	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, brd->brd_queue);



	disk = brd->brd_disk = alloc_disk(1 << part_shift);

	if (!disk)

		goto out_free_queue;