Commit a336d298 authored by Paul Clements's avatar Paul Clements Committed by Linus Torvalds
Browse files

nbd: handle discard requests 



Add discard support to nbd.  If the nbd-server supports discard, it will
send NBD_FLAG_SEND_TRIM to the client.  The client will then set the flag
in the kernel via NBD_SET_FLAGS, which tells the kernel to enable discards
for the device (QUEUE_FLAG_DISCARD).

If discard support is enabled, then when the nbd client system receives a
discard request, this will be passed along to the nbd-server.  When the
discard request is received by the nbd-server, it will perform:

	fallocate(.. FALLOC_FL_PUNCH_HOLE ..)

To punch a hole in the backend storage, which is no longer needed.

Signed-off-by: default avatarPaul Clements <paul.clements@steeleye.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2f012508

drivers/block/nbd.c

+14 −1
Original line number Diff line number Diff line
@@ -98,6 +98,7 @@ static const char *nbdcmd_to_ascii(int cmd) 
	case  NBD_CMD_READ: return "read";

	case NBD_CMD_WRITE: return "write";

	case  NBD_CMD_DISC: return "disconnect";

	case  NBD_CMD_TRIM: return "trim/discard";

	}

	return "invalid";

}
@@ -469,6 +470,10 @@ static void nbd_handle_req(struct nbd_device *nbd, struct request *req) 


	nbd_cmd(req) = NBD_CMD_READ;

	if (rq_data_dir(req) == WRITE) {

		if ((req->cmd_flags & REQ_DISCARD)) {

			WARN_ON(!(nbd->flags & NBD_FLAG_SEND_TRIM));

			nbd_cmd(req) = NBD_CMD_TRIM;

		} else

			nbd_cmd(req) = NBD_CMD_WRITE;

		if (nbd->flags & NBD_FLAG_READ_ONLY) {

			dev_err(disk_to_dev(nbd->disk),
@@ -676,6 +681,10 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd, 


		mutex_unlock(&nbd->tx_lock);



		if (nbd->flags & NBD_FLAG_SEND_TRIM)

			queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,

				nbd->disk->queue);



		thread = kthread_create(nbd_thread, nbd, nbd->disk->disk_name);

		if (IS_ERR(thread)) {

			mutex_lock(&nbd->tx_lock);
@@ -693,6 +702,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd, 
		nbd->file = NULL;

		nbd_clear_que(nbd);

		dev_warn(disk_to_dev(nbd->disk), "queue cleared\n");

		queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);

		if (file)

			fput(file);

		nbd->bytesize = 0;
@@ -811,6 +821,9 @@ static int __init nbd_init(void) 
		 * Tell the block layer that we are not a rotational device

		 */

		queue_flag_set_unlocked(QUEUE_FLAG_NONROT, disk->queue);

		disk->queue->limits.discard_granularity = 512;

		disk->queue->limits.max_discard_sectors = UINT_MAX;

		disk->queue->limits.discard_zeroes_data = 0;

	}



	if (register_blkdev(NBD_MAJOR, "nbd")) {

include/linux/nbd.h

+5 −1
Original line number Diff line number Diff line
@@ -32,12 +32,16 @@ 
enum {

	NBD_CMD_READ = 0,

	NBD_CMD_WRITE = 1,

	NBD_CMD_DISC = 2

	NBD_CMD_DISC = 2,

	/* there is a gap here to match userspace */

	NBD_CMD_TRIM = 4

};



/* values for flags field */

#define NBD_FLAG_HAS_FLAGS    (1 << 0) /* nbd-server supports flags */

#define NBD_FLAG_READ_ONLY    (1 << 1) /* device is read-only */

/* there is a gap here to match userspace */

#define NBD_FLAG_SEND_TRIM    (1 << 5) /* send trim/discard */



#define nbd_cmd(req) ((req)->cmd[0])

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