usb-storage: implement "soft" unbinding

This patch (as1092) implements "soft" unbinding for usb-storage. When
the disconnect routine is called, all commands and reset delays are
allowed to complete normally until after scsi_remove_host() returns.
This means that the commands needed for an orderly shutdown will be
sent through to the device.

Unlike before, the driver will now execute every command that it
accepts. Hence there's no need for special code to catch unexecuted
commands and fail them.

The new sequence of events when disconnect runs goes as follows:

If the device is truly unplugged, set the DISCONNECTING
flag so we won't try to access it any more.

If the SCSI-scanning thread hasn't started up yet, prevent
it from doing anything by setting the new DONT_SCAN flag.
Then wake it up and wait for it to terminate.

Remove the SCSI host. This unbinds the upper-level drivers,
doing an orderly shutdown. Commands sent to quiesce the
device will be transmitted normally, unless the device is
unplugged.

Set the DISCONNECTING flag so that we won't accept any new
commands that might get submitted (there aren't supposed to be
any) and we won't try to access the device for resets.

Tell the control thread to exit by waking it up with no
pending command, and wait for it to terminate.

Go on to do all the other normal stuff: releasing resources,
freeing memory, and so on.

Signed-off-by: Alan Stern <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/storage/transport.c

···
 	long timeleft;
 	int status;
 
-	/* don't submit URBs during abort/disconnect processing */
-	if (us->dflags & ABORTING_OR_DISCONNECTING)
+	/* don't submit URBs during abort processing */
+	if (test_bit(US_FLIDX_ABORTING, &us->dflags))
 		return -EIO;
 
 	/* set up data structures for the wakeup system */
···
 	 * to cancel it */
 	set_bit(US_FLIDX_URB_ACTIVE, &us->dflags);
 
-	/* did an abort/disconnect occur during the submission? */
-	if (us->dflags & ABORTING_OR_DISCONNECTING) {
+	/* did an abort occur during the submission? */
+	if (test_bit(US_FLIDX_ABORTING, &us->dflags)) {
 
 		/* cancel the URB, if it hasn't been cancelled already */
 		if (test_and_clear_bit(US_FLIDX_URB_ACTIVE, &us->dflags)) {
···
 {
 	int result;
 
-	/* don't submit s-g requests during abort/disconnect processing */
-	if (us->dflags & ABORTING_OR_DISCONNECTING)
+	/* don't submit s-g requests during abort processing */
+	if (test_bit(US_FLIDX_ABORTING, &us->dflags))
 		return USB_STOR_XFER_ERROR;
 
 	/* initialize the scatter-gather request block */
···
 	 * okay to cancel it */
 	set_bit(US_FLIDX_SG_ACTIVE, &us->dflags);
 
-	/* did an abort/disconnect occur during the submission? */
-	if (us->dflags & ABORTING_OR_DISCONNECTING) {
+	/* did an abort occur during the submission? */
+	if (test_bit(US_FLIDX_ABORTING, &us->dflags)) {
 
 		/* cancel the request, if it hasn't been cancelled already */
 		if (test_and_clear_bit(US_FLIDX_SG_ACTIVE, &us->dflags)) {

drivers/usb/storage/usb.c

···
 		/* lock the device pointers */
 		mutex_lock(&(us->dev_mutex));
 
-		/* if the device has disconnected, we are free to exit */
-		if (test_bit(US_FLIDX_DISCONNECTING, &us->dflags)) {
-			US_DEBUGP("-- exiting\n");
-			mutex_unlock(&us->dev_mutex);
-			break;
-		}
-
 		/* lock access to the state */
 		scsi_lock(host);
+
+		/* When we are called with no command pending, we're done */
+		if (us->srb == NULL) {
+			scsi_unlock(host);
+			mutex_unlock(&us->dev_mutex);
+			US_DEBUGP("-- exiting\n");
+			break;
+		}
 
 		/* has the command timed out *already* ? */
 		if (test_bit(US_FLIDX_TIMED_OUT, &us->dflags)) {
···
 		/* lock access to the state */
 		scsi_lock(host);
 
-		/* did the command already complete because of a disconnect? */
-		if (!us->srb)
-			;		/* nothing to do */
-
 		/* indicate that the command is done */
-		else if (us->srb->result != DID_ABORT << 16) {
+		if (us->srb->result != DID_ABORT << 16) {
 			US_DEBUGP("scsi cmd done, result=0x%x\n", 
 				   us->srb->result);
 			us->srb->scsi_done(us->srb);
···
 	US_DEBUGP("-- %s\n", __func__);
 
 	/* Tell the control thread to exit.  The SCSI host must
-	 * already have been removed so it won't try to queue
-	 * any more commands.
+	 * already have been removed and the DISCONNECTING flag set
+	 * so that we won't accept any more commands.
 	 */
 	US_DEBUGP("-- sending exit command to thread\n");
-	set_bit(US_FLIDX_DISCONNECTING, &us->dflags);
 	complete(&us->cmnd_ready);
 	if (us->ctl_thread)
 		kthread_stop(us->ctl_thread);
···
 	usb_set_intfdata(us->pusb_intf, NULL);
 }
 
-/* First stage of disconnect processing: stop all commands and remove
- * the host */
+/* First stage of disconnect processing: stop SCSI scanning,
+ * remove the host, and stop accepting new commands
+ */
 static void quiesce_and_remove_host(struct us_data *us)
 {
 	struct Scsi_Host *host = us_to_host(us);
 
-	/* Prevent new USB transfers, stop the current command, and
-	 * interrupt a SCSI-scan or device-reset delay */
+	/* If the device is really gone, cut short reset delays */
+	if (us->pusb_dev->state == USB_STATE_NOTATTACHED)
+		set_bit(US_FLIDX_DISCONNECTING, &us->dflags);
+
+	/* Prevent SCSI-scanning (if it hasn't started yet)
+	 * and wait for the SCSI-scanning thread to stop.
+	 */
+	set_bit(US_FLIDX_DONT_SCAN, &us->dflags);
+	wake_up(&us->delay_wait);
+	wait_for_completion(&us->scanning_done);
+
+	/* Removing the host will perform an orderly shutdown: caches
+	 * synchronized, disks spun down, etc.
+	 */
+	scsi_remove_host(host);
+
+	/* Prevent any new commands from being accepted and cut short
+	 * reset delays.
+	 */
 	scsi_lock(host);
 	set_bit(US_FLIDX_DISCONNECTING, &us->dflags);
 	scsi_unlock(host);
-	usb_stor_stop_transport(us);
 	wake_up(&us->delay_wait);
-
-	/* queuecommand won't accept any new commands and the control
-	 * thread won't execute a previously-queued command.  If there
-	 * is such a command pending, complete it with an error. */
-	mutex_lock(&us->dev_mutex);
-	if (us->srb) {
-		us->srb->result = DID_NO_CONNECT << 16;
-		scsi_lock(host);
-		us->srb->scsi_done(us->srb);
-		us->srb = NULL;
-		complete(&us->notify);		/* in case of an abort */
-		scsi_unlock(host);
-	}
-	mutex_unlock(&us->dev_mutex);
-
-	/* Now we own no commands so it's safe to remove the SCSI host */
-	scsi_remove_host(host);
-
-	/* Wait for the SCSI-scanning thread to stop */
-	wait_for_completion(&us->scanning_done);
 }
 
 /* Second stage of disconnect processing: deallocate all resources */
···
 		printk(KERN_DEBUG "usb-storage: waiting for device "
 				"to settle before scanning\n");
 		wait_event_freezable_timeout(us->delay_wait,
-				test_bit(US_FLIDX_DISCONNECTING, &us->dflags),
+				test_bit(US_FLIDX_DONT_SCAN, &us->dflags),
 				delay_use * HZ);
 	}
 
 	/* If the device is still connected, perform the scanning */
-	if (!test_bit(US_FLIDX_DISCONNECTING, &us->dflags)) {
+	if (!test_bit(US_FLIDX_DONT_SCAN, &us->dflags)) {
 
 		/* For bulk-only devices, determine the max LUN value */
 		if (us->protocol == US_PR_BULK &&
···
 	if (IS_ERR(th)) {
 		printk(KERN_WARNING USB_STORAGE 
 		       "Unable to start the device-scanning thread\n");
+		complete(&us->scanning_done);
 		quiesce_and_remove_host(us);
 		result = PTR_ERR(th);
 		goto BadDevice;
···
 	.pre_reset =	storage_pre_reset,
 	.post_reset =	storage_post_reset,
 	.id_table =	storage_usb_ids,
+	.soft_unbind =	1,
 };
 
 static int __init usb_stor_init(void)

drivers/usb/storage/usb.h

···
 #define US_FLIDX_SG_ACTIVE	1	/* current_sg is in use     */
 #define US_FLIDX_ABORTING	2	/* abort is in progress     */
 #define US_FLIDX_DISCONNECTING	3	/* disconnect in progress   */
-#define ABORTING_OR_DISCONNECTING	((1UL << US_FLIDX_ABORTING) | \
-					 (1UL << US_FLIDX_DISCONNECTING))
 #define US_FLIDX_RESETTING	4	/* device reset in progress */
 #define US_FLIDX_TIMED_OUT	5	/* SCSI midlayer timed out  */
-
+#define US_FLIDX_DONT_SCAN	6	/* don't scan (disconnect)  */
 
 #define USB_STOR_STRING_LEN 32