USB: add API for userspace drivers to "claim" ports

This patch (as1258) implements a feature that users have been asking
for: It gives programs the ability to "claim" a port on a hub, via a
new usbfs ioctl.  A device plugged into a "claimed" port will not be
touched by the kernel beyond the immediate necessities of
initialization and enumeration.

In particular, when a device is plugged into a "claimed" port, the
kernel will not select and install a configuration.  And when a config
is installed by usbfs or sysfs, the kernel will not probe any drivers
for any of the interfaces.  (However the kernel will fetch various
string descriptors during enumeration.  One could argue that this
isn't really necessary, but the strings are exported in sysfs.)

The patch does not guarantee exclusive access to these devices; it is
still possible for more than one program to open the device file
concurrently.  Programs are responsible for coordinating access among
themselves.

A demonstration program showing how to use the new interface can be 
found in an attachment to

	http://marc.info/?l=linux-usb&m=124345857431452&w=2

The patch also makes a small simplification to the hub driver,
replacing a bunch of more-or-less useless variants of "out of memory"
with a single message.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 83 insertions, 5 deletions

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 71f86c60d83c..cb54420ed583 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -78,6 +78,7 @@ struct usb_hub {
 	u8			indicator[USB_MAXCHILDREN];
 	struct delayed_work	leds;
 	struct delayed_work	init_work;
+	void			**port_owners;
 };
 
 
@@ -860,19 +861,17 @@ static int hub_configure(struct usb_hub *hub,
 	u16 wHubCharacteristics;
 	unsigned int pipe;
 	int maxp, ret;
-	char *message;
+	char *message = "out of memory";
 
 	hub->buffer = usb_buffer_alloc(hdev, sizeof(*hub->buffer), GFP_KERNEL,
 			&hub->buffer_dma);
 	if (!hub->buffer) {
-		message = "can't allocate hub irq buffer";
 		ret = -ENOMEM;
 		goto fail;
 	}
 
 	hub->status = kmalloc(sizeof(*hub->status), GFP_KERNEL);
 	if (!hub->status) {
-		message = "can't kmalloc hub status buffer";
 		ret = -ENOMEM;
 		goto fail;
 	}
@@ -880,7 +879,6 @@ static int hub_configure(struct usb_hub *hub,
 
 	hub->descriptor = kmalloc(sizeof(*hub->descriptor), GFP_KERNEL);
 	if (!hub->descriptor) {
-		message = "can't kmalloc hub descriptor";
 		ret = -ENOMEM;
 		goto fail;
 	}
@@ -904,6 +902,12 @@ static int hub_configure(struct usb_hub *hub,
 	dev_info (hub_dev, "%d port%s detected\n", hdev->maxchild,
 		(hdev->maxchild == 1) ? "" : "s");
 
+	hub->port_owners = kzalloc(hdev->maxchild * sizeof(void *), GFP_KERNEL);
+	if (!hub->port_owners) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
 	wHubCharacteristics = le16_to_cpu(hub->descriptor->wHubCharacteristics);
 
 	if (wHubCharacteristics & HUB_CHAR_COMPOUND) {
@@ -1082,7 +1086,6 @@ static int hub_configure(struct usb_hub *hub,
 
 	hub->urb = usb_alloc_urb(0, GFP_KERNEL);
 	if (!hub->urb) {
-		message = "couldn't allocate interrupt urb";
 		ret = -ENOMEM;
 		goto fail;
 	}
@@ -1131,11 +1134,13 @@ static void hub_disconnect(struct usb_interface *intf)
 	hub_quiesce(hub, HUB_DISCONNECT);
 
 	usb_set_intfdata (intf, NULL);
+	hub->hdev->maxchild = 0;
 
 	if (hub->hdev->speed == USB_SPEED_HIGH)
 		highspeed_hubs--;
 
 	usb_free_urb(hub->urb);
+	kfree(hub->port_owners);
 	kfree(hub->descriptor);
 	kfree(hub->status);
 	usb_buffer_free(hub->hdev, sizeof(*hub->buffer), hub->buffer,
@@ -1250,6 +1255,79 @@ hub_ioctl(struct usb_interface *intf, unsigned int code, void *user_data)
 	}
 }
 
+/*
+ * Allow user programs to claim ports on a hub.  When a device is attached
+ * to one of these "claimed" ports, the program will "own" the device.
+ */
+static int find_port_owner(struct usb_device *hdev, unsigned port1,
+		void ***ppowner)
+{
+	if (hdev->state == USB_STATE_NOTATTACHED)
+		return -ENODEV;
+	if (port1 == 0 || port1 > hdev->maxchild)
+		return -EINVAL;
+
+	/* This assumes that devices not managed by the hub driver
+	 * will always have maxchild equal to 0.
+	 */
+	*ppowner = &(hdev_to_hub(hdev)->port_owners[port1 - 1]);
+	return 0;
+}
+
+/* In the following three functions, the caller must hold hdev's lock */
+int usb_hub_claim_port(struct usb_device *hdev, unsigned port1, void *owner)
+{
+	int rc;
+	void **powner;
+
+	rc = find_port_owner(hdev, port1, &powner);
+	if (rc)
+		return rc;
+	if (*powner)
+		return -EBUSY;
+	*powner = owner;
+	return rc;
+}
+
+int usb_hub_release_port(struct usb_device *hdev, unsigned port1, void *owner)
+{
+	int rc;
+	void **powner;
+
+	rc = find_port_owner(hdev, port1, &powner);
+	if (rc)
+		return rc;
+	if (*powner != owner)
+		return -ENOENT;
+	*powner = NULL;
+	return rc;
+}
+
+void usb_hub_release_all_ports(struct usb_device *hdev, void *owner)
+{
+	int n;
+	void **powner;
+
+	n = find_port_owner(hdev, 1, &powner);
+	if (n == 0) {
+		for (; n < hdev->maxchild; (++n, ++powner)) {
+			if (*powner == owner)
+				*powner = NULL;
+		}
+	}
+}
+
+/* The caller must hold udev's lock */
+bool usb_device_is_owned(struct usb_device *udev)
+{
+	struct usb_hub *hub;
+
+	if (udev->state == USB_STATE_NOTATTACHED || !udev->parent)
+		return false;
+	hub = hdev_to_hub(udev->parent);
+	return !!hub->port_owners[udev->portnum - 1];
+}
+
 
 static void recursively_mark_NOTATTACHED(struct usb_device *udev)
 {