usblp: Implement the ENOSPC convention

This patch implements a mode when a printer returns ENOSPC when it runs
out of paper. The default remains the same as before. An application which
wishes to use this function has to enable it explicitly with an ioctl
LPABORT.

This is done on a request by our (Fedora) CUPS guy, Tim Waugh. The API is
similar enough to the lp0's one that CUPS works with both (but see below),
but it's has some differences.

Most importantly, the abort mode is persistent in case of lp0: once tunelp
was run your cat fill blow up until you reboot or run tunelp again. For
usblp, I made it so the abort mode is only in effect as long as device
is open. This way you can mix and match CUPS and cat(1) freely and nothing
bad happens even if you run out of paper. It is also safer in the face
of any unexpected crashes.

It has to be noted that mixing LPABORT and O_NONBLOCK is not advised.
It probably does not do what you want: instead of returning -ENOSPC
it will always return -EAGAIN (because it would otherwise block while
waiting for the paper). Applications which use O_NONBLOCK should continue
to use LPGETSTATUS like before.

Finally, CUPS actually requires patching to take full advantage of this.
It has several components; those which invoke LPABORT work, but some of
them need the ioctl added. This is completely compatible, you can mix
old CUPS and new kernels or vice versa.
Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/class/usblp.c

@@ -69,7 +69,6 @@
 #define USBLP_DEVICE_ID_SIZE	1024
 
 /* ioctls: */
-#define LPGETSTATUS		0x060b		/* same as in drivers/char/lp.c */
 #define IOCNR_GET_DEVICE_ID		1
 #define IOCNR_GET_PROTOCOLS		2
 #define IOCNR_SET_PROTOCOL		3
@@ -159,10 +158,12 @@ struct usblp {
 	int			wstatus;	/* bytes written or error */
 	int			rstatus;	/* bytes ready or error */
 	unsigned int		quirks;			/* quirks flags */
+	unsigned int		flags;			/* mode flags */
 	unsigned char		used;			/* True if open */
 	unsigned char		present;		/* True if not disconnected */
 	unsigned char		bidir;			/* interface is bidirectional */
 	unsigned char		sleeping;		/* interface is suspended */
+	unsigned char		no_paper;		/* Paper Out happened */
 	unsigned char		*device_id_string;	/* IEEE 1284 DEVICE ID string (ptr) */
 							/* first 2 bytes are (big-endian) length */
 };
@@ -325,6 +326,7 @@ static void usblp_bulk_write(struct urb *urb)
 		usblp->wstatus = status;
 	else
 		usblp->wstatus = urb->actual_length;
+	usblp->no_paper = 0;
 	usblp->wcomplete = 1;
 	wake_up(&usblp->wwait);
 	spin_unlock(&usblp->lock);
@@ -411,18 +413,10 @@ static int usblp_open(struct inode *inode, struct file *file)
 		goto out;
 
 	/*
-	 * TODO: need to implement LP_ABORTOPEN + O_NONBLOCK as in drivers/char/lp.c ???
-	 * This is #if 0-ed because we *don't* want to fail an open
-	 * just because the printer is off-line.
+	 * We do not implement LP_ABORTOPEN/LPABORTOPEN for two reasons:
+	 *  - We do not want persistent state which close(2) does not clear
+	 *  - It is not used anyway, according to CUPS people
 	 */
-#if 0
-	if ((retval = usblp_check_status(usblp, 0))) {
-		retval = retval > 1 ? -EIO : -ENOSPC;
-		goto out;
-	}
-#else
-	retval = 0;
-#endif
 
 	retval = usb_autopm_get_interface(intf);
 	if (retval < 0)
@@ -463,6 +457,8 @@ static int usblp_release(struct inode *inode, struct file *file)
 {
 	struct usblp *usblp = file->private_data;
 
+	usblp->flags &= ~LP_ABORT;
+
 	mutex_lock (&usblp_mutex);
 	usblp->used = 0;
 	if (usblp->present) {
@@ -486,7 +482,7 @@ static unsigned int usblp_poll(struct file *file, struct poll_table_struct *wait
 	poll_wait(file, &usblp->wwait, wait);
 	spin_lock_irqsave(&usblp->lock, flags);
 	ret = ((!usblp->bidir || !usblp->rcomplete) ? 0 : POLLIN  | POLLRDNORM)
- 			       | (!usblp->wcomplete ? 0 : POLLOUT | POLLWRNORM);
+	   | ((usblp->no_paper || usblp->wcomplete) ? POLLOUT | POLLWRNORM : 0);
 	spin_unlock_irqrestore(&usblp->lock, flags);
 	return ret;
 }
@@ -675,6 +671,13 @@ static long usblp_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 					retval = -EFAULT;
 				break;
 
+			case LPABORT:
+				if (arg)
+					usblp->flags |= LP_ABORT;
+				else
+					usblp->flags &= ~LP_ABORT;
+				break;
+
 			default:
 				retval = -ENOTTY;
 		}
@@ -730,6 +733,7 @@ static ssize_t usblp_write(struct file *file, const char __user *buffer, size_t
 		if ((rv = usb_submit_urb(writeurb, GFP_KERNEL)) < 0) {
 			usblp->wstatus = 0;
 			spin_lock_irq(&usblp->lock);
+			usblp->no_paper = 0;
 			usblp->wcomplete = 1;
 			wake_up(&usblp->wwait);
 			spin_unlock_irq(&usblp->lock);
@@ -747,12 +751,17 @@ static ssize_t usblp_write(struct file *file, const char __user *buffer, size_t
 				/* Presume that it's going to complete well. */
 				writecount += transfer_length;
 			}
+			if (rv == -ENOSPC) {
+				spin_lock_irq(&usblp->lock);
+				usblp->no_paper = 1;	/* Mark for poll(2) */
+				spin_unlock_irq(&usblp->lock);
+				writecount += transfer_length;
+			}
 			/* Leave URB dangling, to be cleaned on close. */
 			goto collect_error;
 		}
 
 		if (usblp->wstatus < 0) {
-			usblp_check_status(usblp, 0);
 			rv = -EIO;
 			goto collect_error;
 		}
@@ -838,32 +847,36 @@ done:
  * when O_NONBLOCK is set. So, applications setting O_NONBLOCK must use
  * select(2) or poll(2) to wait for the buffer to drain before closing.
  * Alternatively, set blocking mode with fcntl and issue a zero-size write.
- *
- * Old v0.13 code had a non-functional timeout for wait_event(). Someone forgot
- * to check the return code for timeout expiration, so it had no effect.
- * Apparently, it was intended to check for error conditons, such as out
- * of paper. It is going to return when we settle things with CUPS. XXX
  */
 static int usblp_wwait(struct usblp *usblp, int nonblock)
 {
 	DECLARE_WAITQUEUE(waita, current);
 	int rc;
+	int err = 0;
 
 	add_wait_queue(&usblp->wwait, &waita);
 	for (;;) {
+		set_current_state(TASK_INTERRUPTIBLE);
 		if (mutex_lock_interruptible(&usblp->mut)) {
 			rc = -EINTR;
 			break;
 		}
-		set_current_state(TASK_INTERRUPTIBLE);
-		if ((rc = usblp_wtest(usblp, nonblock)) < 0) {
-			mutex_unlock(&usblp->mut);
-			break;
-		}
+		rc = usblp_wtest(usblp, nonblock);
 		mutex_unlock(&usblp->mut);
-		if (rc == 0)
+		if (rc <= 0)
 			break;
-		schedule();
+
+		if (usblp->flags & LP_ABORT) {
+			if (schedule_timeout(msecs_to_jiffies(5000)) == 0) {
+				err = usblp_check_status(usblp, err);
+				if (err == 1) {	/* Paper out */
+					rc = -ENOSPC;
+					break;
+				}
+			}
+		} else {
+			schedule();
+		}
 	}
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&usblp->wwait, &waita);