[RFC PATCH 19/21] usb: Add USB subsystem notifications

From: David Howells
Date: Tue Oct 15 2019 - 17:50:46 EST

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Add a USB subsystem notification mechanism whereby notifications about
hardware events such as device connection, disconnection, reset and I/O
errors, can be reported to a monitoring process asynchronously.

Firstly, an event queue needs to be created:

pipe2(fds, O_TMPFILE);
ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, 256);

then a notification can be set up to report USB notifications via that
queue:

struct watch_notification_filter filter = {
.nr_filters = 1,
.filters = {
[0] = {
.type = WATCH_TYPE_USB_NOTIFY,
.subtype_filter[0] = UINT_MAX;
},
},
};
ioctl(fds[1], IOC_WATCH_QUEUE_SET_FILTER, &filter);
notify_devices(fds[1], 12);

After that, messages will be placed into the queue when events occur on a
USB device or bus. Messages are of the following format:

struct usb_notification {
struct watch_notification watch;
__u32 error;
__u32 reserved;
__u8 name_len;
__u8 name[0];
} *n;

Where:

n->watch.type will be WATCH_TYPE_USB_NOTIFY

n->watch.subtype will be the type of notification, such as
NOTIFY_USB_DEVICE_ADD.

n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
message.

n->watch.info & WATCH_INFO_ID will be the second argument to
device_notify(), shifted.

n->error and n->reserved are intended to convey information such as
error codes, but are currently not used

n->name_len and n->name convey the USB device name as an
unterminated string. This may be truncated - it is currently
limited to a maximum 63 chars.

Note that it is permissible for messages to be of variable length - or, at
least, the length may be dependent on the subtype.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
cc: linux-usb@xxxxxxxxxxxxxxx
---

Documentation/watch_queue.rst | 9 +++++++
drivers/usb/core/Kconfig | 9 +++++++
drivers/usb/core/devio.c | 47 ++++++++++++++++++++++++++++++++++++++
drivers/usb/core/hub.c | 4 +++
include/linux/usb.h | 18 +++++++++++++++
include/uapi/linux/watch_queue.h | 28 ++++++++++++++++++++++-
samples/watch_queue/watch_test.c | 29 +++++++++++++++++++++++
7 files changed, 142 insertions(+), 2 deletions(-)

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
index f2299f631ae8..5321a9cb1ab2 100644
--- a/Documentation/watch_queue.rst
+++ b/Documentation/watch_queue.rst
@@ -12,6 +12,8 @@ opened by userspace. This can be used in conjunction with::

* Block layer event notifications

+ * USB subsystem event notifications
+

The notifications buffers can be enabled by:

@@ -262,6 +264,13 @@ Any particular buffer can be fed from multiple sources. Sources include:
or temporary link loss. Watches of this type are set on the global device
watch list.

+ * WATCH_TYPE_USB_NOTIFY
+
+ Notifications of this type indicate USB subsystem events, such as
+ attachment, removal, reset and I/O errors. Separate events are generated
+ for buses and devices. Watchpoints of this type are set on the global
+ device watch list.
+

Event Filtering
===============
diff --git a/drivers/usb/core/Kconfig b/drivers/usb/core/Kconfig
index ecaacc8ed311..57e7b649e48b 100644
--- a/drivers/usb/core/Kconfig
+++ b/drivers/usb/core/Kconfig
@@ -102,3 +102,12 @@ config USB_AUTOSUSPEND_DELAY
The default value Linux has always had is 2 seconds. Change
this value if you want a different delay and cannot modify
the command line or module parameter.
+
+config USB_NOTIFICATIONS
+ bool "Provide USB hardware event notifications"
+ depends on USB && DEVICE_NOTIFICATIONS
+ help
+ This option provides support for getting hardware event notifications
+ on USB devices and interfaces. This makes use of the
+ /dev/watch_queue misc device to handle the notification buffer.
+ device_notify(2) is used to set/remove watches.
diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index 3f899552f6e3..693a5657dba3 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -41,6 +41,7 @@
#include <linux/dma-mapping.h>
#include <asm/byteorder.h>
#include <linux/moduleparam.h>
+#include <linux/watch_queue.h>

#include "usb.h"

@@ -2748,13 +2749,59 @@ static void usbdev_remove(struct usb_device *udev)
mutex_unlock(&usbfs_mutex);
}

+#ifdef CONFIG_USB_NOTIFICATIONS
+static noinline void post_usb_notification(const char *devname,
+ enum usb_notification_type subtype,
+ u32 error)
+{
+ unsigned int name_len, n_len;
+ u64 id = 0; /* We can put a device ID here for separate dev watches */
+
+ struct {
+ struct usb_notification n;
+ char more_name[USB_NOTIFICATION_MAX_NAME_LEN -
+ (sizeof(struct usb_notification) -
+ offsetof(struct usb_notification, name))];
+ } n;
+
+ name_len = strlen(devname);
+ name_len = min_t(size_t, name_len, USB_NOTIFICATION_MAX_NAME_LEN);
+ n_len = offsetof(struct usb_notification, name) + name_len;
+
+ memset(&n, 0, sizeof(n));
+ memcpy(n.n.name, devname, n_len);
+
+ n.n.watch.type = WATCH_TYPE_USB_NOTIFY;
+ n.n.watch.subtype = subtype;
+ n.n.watch.info = n_len;
+ n.n.error = error;
+ n.n.name_len = name_len;
+
+ post_device_notification(&n.n.watch, id);
+}
+
+void post_usb_device_notification(const struct usb_device *udev,
+ enum usb_notification_type subtype, u32 error)
+{
+ post_usb_notification(dev_name(&udev->dev), subtype, error);
+}
+
+void post_usb_bus_notification(const struct usb_bus *ubus,
+ enum usb_notification_type subtype, u32 error)
+{
+ post_usb_notification(ubus->bus_name, subtype, error);
+}
+#endif
+
static int usbdev_notify(struct notifier_block *self,
unsigned long action, void *dev)
{
switch (action) {
case USB_DEVICE_ADD:
+ post_usb_device_notification(dev, NOTIFY_USB_DEVICE_ADD, 0);
break;
case USB_DEVICE_REMOVE:
+ post_usb_device_notification(dev, NOTIFY_USB_DEVICE_REMOVE, 0);
usbdev_remove(dev);
break;
}
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 236313f41f4a..e8ebacc15a32 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -29,6 +29,7 @@
#include <linux/random.h>
#include <linux/pm_qos.h>
#include <linux/kobject.h>
+#include <linux/watch_queue.h>

#include <linux/uaccess.h>
#include <asm/byteorder.h>
@@ -4605,6 +4606,9 @@ hub_port_init(struct usb_hub *hub, struct usb_device *udev, int port1,
(udev->config) ? "reset" : "new", speed,
devnum, driver_name);

+ if (udev->config)
+ post_usb_device_notification(udev, NOTIFY_USB_DEVICE_RESET, 0);
+
/* Set up TT records, if needed */
if (hdev->tt) {
udev->tt = hdev->tt;
diff --git a/include/linux/usb.h b/include/linux/usb.h
index e656e7b4b1e4..93fa0666f95a 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -26,6 +26,7 @@
struct usb_device;
struct usb_driver;
struct wusb_dev;
+enum usb_notification_type;

/*-------------------------------------------------------------------------*/

@@ -2015,6 +2016,23 @@ extern void usb_led_activity(enum usb_led_event ev);
static inline void usb_led_activity(enum usb_led_event ev) {}
#endif

+/*
+ * Notification functions.
+ */
+#ifdef CONFIG_USB_NOTIFICATIONS
+extern void post_usb_device_notification(const struct usb_device *udev,
+ enum usb_notification_type subtype,
+ u32 error);
+extern void post_usb_bus_notification(const struct usb_bus *ubus,
+ enum usb_notification_type subtype,
+ u32 error);
+#else
+static inline void post_usb_device_notification(const struct usb_device *udev,
+ unsigned int subtype, u32 error) {}
+static inline void post_usb_bus_notification(const struct usb_bus *ubus,
+ unsigned int subtype, u32 error) {}
+#endif
+
#endif /* __KERNEL__ */

#endif
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 65b127ca272b..f6aa1e39ceea 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -12,7 +12,8 @@ enum watch_notification_type {
WATCH_TYPE_META = 0, /* Special record */
WATCH_TYPE_KEY_NOTIFY = 1, /* Key change event notification */
WATCH_TYPE_BLOCK_NOTIFY = 2, /* Block layer event notification */
- WATCH_TYPE___NR = 3
+ WATCH_TYPE_USB_NOTIFY = 3, /* USB subsystem event notification */
+ WATCH_TYPE___NR = 4
};

enum watch_meta_notification_subtype {
@@ -126,4 +127,29 @@ struct block_notification {
__u64 sector; /* Affected sector */
};

+/*
+ * Type of USB layer notification.
+ */
+enum usb_notification_type {
+ NOTIFY_USB_DEVICE_ADD = 0, /* USB device added */
+ NOTIFY_USB_DEVICE_REMOVE = 1, /* USB device removed */
+ NOTIFY_USB_DEVICE_RESET = 2, /* USB device reset */
+ NOTIFY_USB_DEVICE_ERROR = 3, /* USB device error */
+};
+
+/*
+ * USB subsystem notification record.
+ * - watch.type = WATCH_TYPE_USB_NOTIFY
+ * - watch.subtype = enum usb_notification_type
+ */
+struct usb_notification {
+ struct watch_notification watch; /* WATCH_TYPE_USB_NOTIFY */
+ __u32 error;
+ __u32 reserved;
+ __u8 name_len; /* Length of device name */
+ __u8 name[0]; /* Device name (padded to __u64, truncated at 63 chars) */
+};
+
+#define USB_NOTIFICATION_MAX_NAME_LEN 63
+
#endif /* _UAPI_LINUX_WATCH_QUEUE_H */
diff --git a/samples/watch_queue/watch_test.c b/samples/watch_queue/watch_test.c
index 263dbba59651..ca3d55208852 100644
--- a/samples/watch_queue/watch_test.c
+++ b/samples/watch_queue/watch_test.c
@@ -85,6 +85,26 @@ static void saw_block_change(struct watch_notification *n, size_t len)
(unsigned long long)b->sector);
}

+static const char *usb_subtypes[256] = {
+ [NOTIFY_USB_DEVICE_ADD] = "dev-add",
+ [NOTIFY_USB_DEVICE_REMOVE] = "dev-remove",
+ [NOTIFY_USB_DEVICE_RESET] = "dev-reset",
+ [NOTIFY_USB_DEVICE_ERROR] = "dev-error",
+};
+
+static void saw_usb_event(struct watch_notification *n, size_t len)
+{
+ struct usb_notification *u = (struct usb_notification *)n;
+
+ if (len < sizeof(struct usb_notification))
+ return;
+
+ printf("USB %*.*s %s e=%x r=%x\n",
+ u->name_len, u->name_len, u->name,
+ usb_subtypes[n->subtype],
+ u->error, u->reserved);
+}
+
/*
* Consume and display events.
*/
@@ -161,6 +181,9 @@ static void consumer(int fd)
case WATCH_TYPE_BLOCK_NOTIFY:
saw_block_change(&n.n, len);
break;
+ case WATCH_TYPE_USB_NOTIFY:
+ saw_usb_event(&n.n, len);
+ break;
default:
printf("other type\n");
break;
@@ -172,7 +195,7 @@ static void consumer(int fd)
}

static struct watch_notification_filter filter = {
- .nr_filters = 2,
+ .nr_filters = 3,
.filters = {
[0] = {
.type = WATCH_TYPE_KEY_NOTIFY,
@@ -182,6 +205,10 @@ static struct watch_notification_filter filter = {
.type = WATCH_TYPE_BLOCK_NOTIFY,
.subtype_filter[0] = UINT_MAX,
},
+ [2] = {
+ .type = WATCH_TYPE_USB_NOTIFY,
+ .subtype_filter[0] = UINT_MAX,
+ },
},
};

Next message: David Howells: "[RFC PATCH 20/21] selinux: Implement the watch_key security hook"
Previous message: Thomas Gleixner: "RE: x86/random: Speculation to the rescue"
In reply to: David Howells: "[RFC PATCH 18/21] block: Add block layer notifications"
Next in thread: David Howells: "[RFC PATCH 20/21] selinux: Implement the watch_key security hook"
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