On 12/04/2012 08:11 PM, James Bottomley wrote:

On Mon, 2012-12-03 at 08:23 -0800, Tejun Heo wrote:

quoted

Hello, James.

On Mon, Dec 03, 2012 at 08:25:43AM +0000, James Bottomley wrote:

quoted

quoted

diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index e65c62e..1756151 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h

@@ -160,6 +160,7 @@ struct scsi_device {
 	unsigned can_power_off:1; /* Device supports runtime power off */
 	unsigned wce_default_on:1;	/* Cache is ON by default */
 	unsigned no_dif:1;	/* T10 PI (DIF) should be disabled */
+	unsigned event_driven:1; /* No need to poll the device */
 
 	DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
 	struct list_head event_list;	/* asserted events */

Yes, but if we can get away with doing that, it should be in genhd
because it's completely generic.

I was imagining we'd have to fake the reply to the test unit ready or
some other commands, which is why it would need to be in sr.c

The check events code is Tejun's baby, if he's OK with it then just do
it in genhd.c

The problem here is there's no easy to reach genhd from libata (or the
other way around) without going through sr.  I think we're gonna have
to have something in sr one way or the other.

Can't we do that via an event? It's a bit clunky because we need the
callback in the layer that sees the sdev, which is libata-scsi, we just
need an analogue of ata_scsi_media_change_notify, but ignoring and
allowing polling is essentially event driven as well, so it should all
work.  We'll need a listener in genhd, which might be trickier.

Hi Tejun,

Do you have any comments on James' suggestion? I want to know your
opinion, thanks.

Hi James,

Do you mean we start a thread in genhd that listen to events, so that
some driver can send an event to genhd about if the device should be
polled? I'm thinking where to store such information. If store it in
struct disk_events, then we will need to know which gendisk is for
the device, but how? Maybe by loop scan all gendisk's driverfs_dev?
If store it in struct device, then we do not need to send the event but
just set a flag in sturct device in libata, and let genhd check this
flag when poll. So I don't quite understand this, can you please
elaborate? Thanks.

Thanks,
Aaron

This may also work as the more generic route for stuff where we can't
connect the bottom to the top of the stack (which looks like a problem
we'll begin wrestling with a lot now).

James