Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754763AbWKIIZF (ORCPT ); Thu, 9 Nov 2006 03:25:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754760AbWKIIYt (ORCPT ); Thu, 9 Nov 2006 03:24:49 -0500 Received: from dea.vocord.ru ([217.67.177.50]:28649 "EHLO kano.factory.vocord.ru") by vger.kernel.org with ESMTP id S1754709AbWKIIYe convert rfc822-to-8bit (ORCPT ); Thu, 9 Nov 2006 03:24:34 -0500 Cc: David Miller , Ulrich Drepper , Andrew Morton , Evgeniy Polyakov , netdev , Zach Brown , Christoph Hellwig , Chase Venters , Johann Borck , linux-kernel@vger.kernel.org, Jeff Garzik Subject: [take24 1/6] kevent: Description. In-Reply-To: <11630606361046@2ka.mipt.ru> X-Mailer: gregkh_patchbomb Date: Thu, 9 Nov 2006 11:23:56 +0300 Message-Id: <1163060636219@2ka.mipt.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Reply-To: Evgeniy Polyakov To: Evgeniy Polyakov Content-Transfer-Encoding: 7BIT From: Evgeniy Polyakov Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 8870 Lines: 202 Description. diff --git a/Documentation/kevent.txt b/Documentation/kevent.txt new file mode 100644 index 0000000..ca49e4b --- /dev/null +++ b/Documentation/kevent.txt @@ -0,0 +1,186 @@ +Description. + +int kevent_ctl(int fd, unsigned int cmd, unsigned int num, struct ukevent *arg); + +fd - is the file descriptor referring to the kevent queue to manipulate. +It is created by opening "/dev/kevent" char device, which is created with +dynamic minor number and major number assigned for misc devices. + +cmd - is the requested operation. It can be one of the following: + KEVENT_CTL_ADD - add event notification + KEVENT_CTL_REMOVE - remove event notification + KEVENT_CTL_MODIFY - modify existing notification + +num - number of struct ukevent in the array pointed to by arg +arg - array of struct ukevent + +When called, kevent_ctl will carry out the operation specified in the +cmd parameter. +------------------------------------------------------------------------------- + + int kevent_get_events(int ctl_fd, unsigned int min_nr, unsigned int max_nr, + __u64 timeout, struct ukevent *buf, unsigned flags) + +ctl_fd - file descriptor referring to the kevent queue +min_nr - minimum number of completed events that kevent_get_events will block + waiting for +max_nr - number of struct ukevent in buf +timeout - number of nanoseconds to wait before returning less than min_nr + events. If this is -1, then wait forever. +buf - pointer to an array of struct ukevent. +flags - unused + +kevent_get_events will wait timeout milliseconds for at least min_nr completed +events, copying completed struct ukevents to buf and deleting any +KEVENT_REQ_ONESHOT event requests. In nonblocking mode it returns as many +events as possible, but not more than max_nr. In blocking mode it waits until +timeout or if at least min_nr events are ready. +------------------------------------------------------------------------------- + + int kevent_wait(int ctl_fd, unsigned int num, __u64 timeout) + +ctl_fd - file descriptor referring to the kevent queue +num - number of processed kevents +timeout - this timeout specifies number of nanoseconds to wait until there is + free space in kevent queue + +This syscall waits until either timeout expires or at least one event becomes +ready. It also copies that num events into special ring buffer and requeues +them (or removes depending on flags). +------------------------------------------------------------------------------- + + int kevent_ring_init(int ctl_fd, struct kevent_ring *ring, unsigned int num) + +ctl_fd - file descriptor referring to the kevent queue +num - size of the ring buffer in events + + struct kevent_ring + { + unsigned int ring_kidx; + struct ukevent event[0]; + } + +ring_kidx - is an index in the ring buffer where kernel will put new events + when kevent_wait() or kevent_get_events() is called + +Example userspace code (ring_buffer.c) can be found on project's homepage. + +Each kevent syscall can be so called cancellation point in glibc, i.e. when +thread has been cancelled in kevent syscall, thread can be safely removed +and no events will be lost, since each syscall (kevent_wait() or +kevent_get_events()) will copy event into special ring buffer, accessible +from other threads or even processes (if shared memory is used). + +When kevent is removed (not dequeued when it is ready, but just removed), +even if it was ready, it is not copied into ring buffer, since if it is +removed, no one cares about it (otherwise user would wait until it becomes +ready and got it through usual way using kevent_get_events() or kevent_wait()) +and thus no need to copy it to the ring buffer. + +It is possible with userspace ring buffer, that events in the ring buffer +can be replaced without knowledge for the thread currently reading them +(when other thread calls kevent_get_events() or kevent_wait()), so appropriate +locking between threads or processes, which can simultaneously access the same +ring buffer, is required. +------------------------------------------------------------------------------- + +The bulk of the interface is entirely done through the ukevent struct. +It is used to add event requests, modify existing event requests, +specify which event requests to remove, and return completed events. + +struct ukevent contains the following members: + +struct kevent_id id + Id of this request, e.g. socket number, file descriptor and so on +__u32 type + Event type, e.g. KEVENT_SOCK, KEVENT_INODE, KEVENT_TIMER and so on +__u32 event + Event itself, e.g. SOCK_ACCEPT, INODE_CREATED, TIMER_FIRED +__u32 req_flags + Per-event request flags, + + KEVENT_REQ_ONESHOT + event will be removed when it is ready + + KEVENT_REQ_WAKEUP_ONE + When several threads wait on the same kevent queue and requested the + same event, for example 'wake me up when new client has connected, + so I could call accept()', then all threads will be awakened when new + client has connected, but only one of them can process the data. This + problem is known as thundering nerd problem. Events which have this + flag set will not be marked as ready (and appropriate threads will + not be awakened) if at least one event has been already marked. + + KEVENT_REQ_ET + Edge Triggered behaviour. It is an optimisation which allows to move + ready and dequeued (i.e. copied to userspace) event to move into set + of interest for given storage (socket, inode and so on) again. It is + very usefull for cases when the same event should be used many times + (like reading from pipe). It is similar to epoll()'s EPOLLET flag. + + KEVENT_REQ_LAST_CHECK + if set allows to perform the last check on kevent (call appropriate + callback) when kevent is marked as ready and has been removed from + ready queue. If it will be confirmed that kevent is ready + (k->callbacks.callback(k) returns true) then kevent will be copied + to userspace, otherwise it will be requeued back to storage. + Second (checking) call is performed with this bit cleared, so callback + can detect when it was called from kevent_storage_ready() - bit is set, + or kevent_dequeue_ready() - bit is cleared. If kevent will be requeued, + bit will be set again. + +__u32 ret_flags + Per-event return flags + + KEVENT_RET_BROKEN + Kevent is broken + + KEVENT_RET_DONE + Kevent processing was finished successfully + + KEVENT_RET_COPY_FAILED + Kevent was not copied into ring buffer due to some error conditions. + +__u32 ret_data + Event return data. Event originator fills it with anything it likes + (for example timer notifications put number of milliseconds when timer + has fired +union { __u32 user[2]; void *ptr; } + User's data. It is not used, just copied to/from user. The whole structure + is aligned to 8 bytes already, so the last union is aligned properly. + +------------------------------------------------------------------------------- + +Usage + +For KEVENT_CTL_ADD, all fields relevant to the event type must be filled +(id, type, possibly event, req_flags). +After kevent_ctl(..., KEVENT_CTL_ADD, ...) returns each struct's ret_flags +should be checked to see if the event is already broken or done. + +For KEVENT_CTL_MODIFY, the id, req_flags, and user and event fields must be +set and an existing kevent request must have matching id and user fields. If +match is found, req_flags and event are replaced with the newly supplied +values and requeueing is started, so modified kevent can be checked and +probably marked as ready immediately. If a match can't be found, the +passed in ukevent's ret_flags has KEVENT_RET_BROKEN set. KEVENT_RET_DONE is +always set. + +For KEVENT_CTL_REMOVE, the id and user fields must be set and an existing +kevent request must have matching id and user fields. If a match is found, +the kevent request is removed. If a match can't be found, the passed in +ukevent's ret_flags has KEVENT_RET_BROKEN set. KEVENT_RET_DONE is always set. + +For kevent_get_events, the entire structure is returned. + +------------------------------------------------------------------------------- + +Usage cases + +kevent_timer +struct ukevent should contain following fields: + type - KEVENT_TIMER + event - KEVENT_TIMER_FIRED + req_flags - KEVENT_REQ_ONESHOT if you want to fire that timer only once + id.raw[0] - number of seconds after commit when this timer shout expire + id.raw[0] - additional to number of seconds number of nanoseconds - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/