USB: usbfs: allow URBs to be reaped after disconnection

The usbfs API has a peculiar hole: Users are not allowed to reap their
URBs after the device has been disconnected.  There doesn't seem to be
any good reason for this; it is an ad-hoc inconsistency.

The patch allows users to issue the USBDEVFS_REAPURB and
USBDEVFS_REAPURBNDELAY ioctls (together with their 32-bit counterparts
on 64-bit systems) even after the device is gone.  If no URBs are
pending for a disconnected device then the ioctls will return -ENODEV
rather than -EAGAIN, because obviously no new URBs will ever be able
to complete.

The patch also adds a new capability flag for
USBDEVFS_GET_CAPABILITIES to indicate that the reap-after-disconnect
feature is supported.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Tested-by: Chris Dickens <christopher.a.dickens@gmail.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>

drivers/usb/core/devio.c

@@ -1689,7 +1689,7 @@ static struct async *reap_as(struct usb_dev_state *ps)
 	for (;;) {
 		__set_current_state(TASK_INTERRUPTIBLE);
 		as = async_getcompleted(ps);
-		if (as)
+		if (as || !connected(ps))
 			break;
 		if (signal_pending(current))
 			break;
@@ -1712,7 +1712,7 @@ static int proc_reapurb(struct usb_dev_state *ps, void __user *arg)
 	}
 	if (signal_pending(current))
 		return -EINTR;
-	return -EIO;
+	return -ENODEV;
 }
 
 static int proc_reapurbnonblock(struct usb_dev_state *ps, void __user *arg)
@@ -1721,10 +1721,11 @@ static int proc_reapurbnonblock(struct usb_dev_state *ps, void __user *arg)
 	struct async *as;
 
 	as = async_getcompleted(ps);
-	retval = -EAGAIN;
 	if (as) {
 		retval = processcompl(as, (void __user * __user *)arg);
 		free_async(as);
+	} else {
+		retval = (connected(ps) ? -EAGAIN : -ENODEV);
 	}
 	return retval;
 }
@@ -1854,7 +1855,7 @@ static int proc_reapurb_compat(struct usb_dev_state *ps, void __user *arg)
 	}
 	if (signal_pending(current))
 		return -EINTR;
-	return -EIO;
+	return -ENODEV;
 }
 
 static int proc_reapurbnonblock_compat(struct usb_dev_state *ps, void __user *arg)
@@ -1862,11 +1863,12 @@ static int proc_reapurbnonblock_compat(struct usb_dev_state *ps, void __user *ar
 	int retval;
 	struct async *as;
 
-	retval = -EAGAIN;
 	as = async_getcompleted(ps);
 	if (as) {
 		retval = processcompl_compat(as, (void __user * __user *)arg);
 		free_async(as);
+	} else {
+		retval = (connected(ps) ? -EAGAIN : -ENODEV);
 	}
 	return retval;
 }
@@ -2038,7 +2040,8 @@ static int proc_get_capabilities(struct usb_dev_state *ps, void __user *arg)
 {
 	__u32 caps;
 
-	caps = USBDEVFS_CAP_ZERO_PACKET | USBDEVFS_CAP_NO_PACKET_SIZE_LIM;
+	caps = USBDEVFS_CAP_ZERO_PACKET | USBDEVFS_CAP_NO_PACKET_SIZE_LIM |
+			USBDEVFS_CAP_REAP_AFTER_DISCONNECT;
 	if (!ps->dev->bus->no_stop_on_short)
 		caps |= USBDEVFS_CAP_BULK_CONTINUATION;
 	if (ps->dev->bus->sg_tablesize)
@@ -2138,6 +2141,32 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
 		return -EPERM;
 
 	usb_lock_device(dev);
+
+	/* Reap operations are allowed even after disconnection */
+	switch (cmd) {
+	case USBDEVFS_REAPURB:
+		snoop(&dev->dev, "%s: REAPURB\n", __func__);
+		ret = proc_reapurb(ps, p);
+		goto done;
+
+	case USBDEVFS_REAPURBNDELAY:
+		snoop(&dev->dev, "%s: REAPURBNDELAY\n", __func__);
+		ret = proc_reapurbnonblock(ps, p);
+		goto done;
+
+#ifdef CONFIG_COMPAT
+	case USBDEVFS_REAPURB32:
+		snoop(&dev->dev, "%s: REAPURB32\n", __func__);
+		ret = proc_reapurb_compat(ps, p);
+		goto done;
+
+	case USBDEVFS_REAPURBNDELAY32:
+		snoop(&dev->dev, "%s: REAPURBNDELAY32\n", __func__);
+		ret = proc_reapurbnonblock_compat(ps, p);
+		goto done;
+#endif
+	}
+
 	if (!connected(ps)) {
 		usb_unlock_device(dev);
 		return -ENODEV;
@@ -2231,16 +2260,6 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
 			inode->i_mtime = CURRENT_TIME;
 		break;
 
-	case USBDEVFS_REAPURB32:
-		snoop(&dev->dev, "%s: REAPURB32\n", __func__);
-		ret = proc_reapurb_compat(ps, p);
-		break;
-
-	case USBDEVFS_REAPURBNDELAY32:
-		snoop(&dev->dev, "%s: REAPURBNDELAY32\n", __func__);
-		ret = proc_reapurbnonblock_compat(ps, p);
-		break;
-
 	case USBDEVFS_IOCTL32:
 		snoop(&dev->dev, "%s: IOCTL32\n", __func__);
 		ret = proc_ioctl_compat(ps, ptr_to_compat(p));
@@ -2252,16 +2271,6 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
 		ret = proc_unlinkurb(ps, p);
 		break;
 
-	case USBDEVFS_REAPURB:
-		snoop(&dev->dev, "%s: REAPURB\n", __func__);
-		ret = proc_reapurb(ps, p);
-		break;
-
-	case USBDEVFS_REAPURBNDELAY:
-		snoop(&dev->dev, "%s: REAPURBNDELAY\n", __func__);
-		ret = proc_reapurbnonblock(ps, p);
-		break;
-
 	case USBDEVFS_DISCSIGNAL:
 		snoop(&dev->dev, "%s: DISCSIGNAL\n", __func__);
 		ret = proc_disconnectsignal(ps, p);
@@ -2304,6 +2313,8 @@ static long usbdev_do_ioctl(struct file *file, unsigned int cmd,
 		ret = proc_free_streams(ps, p);
 		break;
 	}
+
+ done:
 	usb_unlock_device(dev);
 	if (ret >= 0)
 		inode->i_atime = CURRENT_TIME;

include/uapi/linux/usbdevice_fs.h

@@ -128,11 +128,12 @@ struct usbdevfs_hub_portinfo {
 	char port [127];	/* e.g. port 3 connects to device 27 */
 };
 
-/* Device capability flags */
+/* System and bus capability flags */
 #define USBDEVFS_CAP_ZERO_PACKET		0x01
 #define USBDEVFS_CAP_BULK_CONTINUATION		0x02
 #define USBDEVFS_CAP_NO_PACKET_SIZE_LIM		0x04
 #define USBDEVFS_CAP_BULK_SCATTER_GATHER	0x08
+#define USBDEVFS_CAP_REAP_AFTER_DISCONNECT	0x10
 
 /* USBDEVFS_DISCONNECT_CLAIM flags & struct */