Re: swsusp: don't eat ide disks

[Linus Torvalds]

On Sun, 3 Nov 2002, Pavel Machek wrote:
> 
> How do I quiesce a queue? Is it ll_rw_blk stuff?

Just send a request down the request list, and make sure that

 - the command is marked as being non-mergeable or re-orderable by 
   software (as all special commands are)

 - the command is not re-orderable / mergeable by hardware (and since the
   command in question would be something like "flush" or "spindown",
   hardware really would be quite broken if it re-ordered it ;)

and then just wait for its completion.

The code is not that complicated, it looks roughly something like

	struct request *rq;

	rq = blk_get_request(q, WRITE, __GFP_WAIT);
	rq->flags = REQ_BLOCK_PC;
	rq->data = NULL;
	rq->data_len = 0;
	rq->timeout = 5*HZ; /* Or whatever */
	memset(rq->cmd, 0, sizeof(rq->cmd));
	rq->cmd[0] = SYNCHRONIZE_CACHE;
	.. fill in whatever bytes the SYNCHRONIZE_CACHE cmd needs ..
	rq->cmd_len = 10;
	err = blk_do_rq(q, bdev, rq);
	blk_put_request(rq);

and you're done. The above should work pretty much on all block drivers
out there, btw: the ones that don't understand SCSI commands should just
ignore requests that aren't the regular REQ_CMD commands.

See drivers/block/scsi_ioctl.c for other examples of sending down commands 
to block devices.

		Linus