[PATCH 12/13] usb: Add USB subsystem notifications [ver #4]

David Howells
2019-06-07T14:19:25Z

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:

fd = open("/dev/event_queue", O_RDWR);
ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);

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(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
notify_devices(fd, 12);

After that, records will be placed into the queue when events occur on a
USB device or bus. Records 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
record.

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 event records to be of variable length -
or, at least, the length may be dependent on the subtype.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: linux-usb@vger.kernel.org
---

Documentation/watch_queue.rst | 9 ++++++
drivers/usb/core/Kconfig | 10 +++++++
drivers/usb/core/devio.c | 55 ++++++++++++++++++++++++++++++++++++++
drivers/usb/core/hub.c | 3 ++
include/linux/usb.h | 19 +++++++++++++
include/uapi/linux/watch_queue.h | 30 ++++++++++++++++++++-
6 files changed, 125 insertions(+), 1 deletion(-)

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
index c2954e191989..7ce5d4147fa9 100644
--- a/Documentation/watch_queue.rst
+++ b/Documentation/watch_queue.rst
@@ -15,6 +15,8 @@ receive notifications from the kernel. This can be used in conjunction with::

* Block layer event notifications

+ * USB subsystem event notifications
+

The notifications buffers can be enabled by:

@@ -344,6 +346,13 @@ Any particular buffer can be fed from multiple sources. Sources include:
or temporary link loss. Watchpoints 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 bdb6bd0b63a6..4be88368ab6b 100644
--- a/drivers/usb/core/Kconfig
+++ b/drivers/usb/core/Kconfig
@@ -103,3 +103,13 @@ 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
+ select 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 fa783531ee88..af7f339c35c5 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"

@@ -2633,13 +2634,67 @@ static void usbdev_remove(struct usb_device *udev)
}
}

+#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; /* Might want to put a dev# here. */
+
+ 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 = round_up(offsetof(struct usb_notification, name) + name_len,
+ sizeof(__u64));
+
+ 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;
+ case USB_BUS_ADD:
+ post_usb_bus_notification(dev, NOTIFY_USB_BUS_ADD, 0);
+ break;
+ case USB_BUS_REMOVE:
+ post_usb_bus_notification(dev, NOTIFY_USB_BUS_REMOVE, 0);
usbdev_remove(dev);
break;
}
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 2f94568ba385..722013d8142c 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -4596,6 +4596,9 @@ 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 ae82d9d1112b..12687b55811d 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -2008,6 +2008,25 @@ 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,
+ enum usb_notification_type subtype,
+ u32 error) {}
+static inline void post_usb_bus_notification(const struct usb_bus *ubus,
+ enum usb_notification_type subtype,
+ u32 error) {}
+#endif
+
#endif /* __KERNEL__ */

#endif
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 22e3326b83a6..d596ac5a61e4 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -14,7 +14,8 @@ enum watch_notification_type {
WATCH_TYPE_SB_NOTIFY = 2, /* Superblock notification */
WATCH_TYPE_KEY_NOTIFY = 3, /* Key/keyring change notification */
WATCH_TYPE_BLOCK_NOTIFY = 4, /* Block layer notifications */
-#define WATCH_TYPE___NR 5
+ WATCH_TYPE_USB_NOTIFY = 5, /* USB subsystem notifications */
+#define WATCH_TYPE___NR 6
};

enum watch_meta_notification_subtype {
@@ -182,4 +183,31 @@ 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_BUS_ADD = 2, /* USB bus added */
+ NOTIFY_USB_BUS_REMOVE = 3, /* USB bus removed */
+ NOTIFY_USB_DEVICE_RESET = 4, /* USB device reset */
+ NOTIFY_USB_DEVICE_ERROR = 5, /* 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 */