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SubjectRe: [PATCH 8/9] usb: Add USB subsystem notifications [ver #5]
On Fri, Jun 28, 2019 at 04:49:49PM +0100, David Howells wrote:
> 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

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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