On Fri, Jun 28, 2019 at 04:48:34PM +0100, David Howells wrote: > Add UAPI definitions for the general notification ring, including the > following pieces: > > (1) struct watch_notification. > > This is the metadata header for each entry in the ring. It includes a > type and subtype that indicate the source of the message > (eg. WATCH_TYPE_MOUNT_NOTIFY) and the kind of the message > (eg. NOTIFY_MOUNT_NEW_MOUNT). > > The header also contains an information field that conveys the > following information: > > - WATCH_INFO_LENGTH. The size of the entry (entries are variable > length). > > - WATCH_INFO_ID. The watch ID specified when the watchpoint was > set. > > - WATCH_INFO_TYPE_INFO. (Sub)type-specific information. > > - WATCH_INFO_FLAG_*. Flag bits overlain on the type-specific > information. For use by the type. > > All the information in the header can be used in filtering messages at > the point of writing into the buffer. > > (2) struct watch_queue_buffer. > > This describes the layout of the ring. Note that the first slots in > the ring contain a special metadata entry that contains the ring > pointers. The producer in the kernel knows to skip this and it has a > proper header (WATCH_TYPE_META, WATCH_META_SKIP_NOTIFICATION) that > indicates the size so that the ring consumer can handle it the same as > any other record and just skip it. > > Note that this means that ring entries can never be split over the end > of the ring, so if an entry would need to be split, a skip record is > inserted to wrap the ring first; this is also WATCH_TYPE_META, > WATCH_META_SKIP_NOTIFICATION. > > (3) WATCH_INFO_NOTIFICATIONS_LOST. > > This is a flag that can be set in the metadata header by the kernel to > indicate that at least one message was lost since it was last cleared > by userspace. > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
