usb: Add USB subsystem notifications
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
6 files changed
