From mboxrd@z Thu Jan 1 00:00:00 1970 From: josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org Subject: Re: [PATCH RFC 0/6] epoll: Introduce new syscall "epoll_mod_wait" Date: Tue, 20 Jan 2015 15:03:52 -0800 Message-ID: <20150120230352.GB14475@cloud> References: <1421747878-30744-1-git-send-email-famz@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Fam Zheng , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , X86 ML , Alexander Viro , Andrew Morton , Kees Cook , David Herrmann , Alexei Starovoitov , Miklos Szeredi , David Drysdale , Oleg Nesterov , "David S. Miller" , Vivek Goyal , Mike Frysinger , Theodore Ts'o , Heiko Carstens , Rasmus Villemoes , Rashika Kheria , Hugh Dickins , Mathieu Desnoyers Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-fsdevel.vger.kernel.org On Tue, Jan 20, 2015 at 02:40:32PM -0800, Andy Lutomirski wrote: > On Tue, Jan 20, 2015 at 1:57 AM, Fam Zheng wrote: > > This adds a new system call, epoll_mod_wait. It's described as below: > > > > NAME > > epoll_mod_wait - modify and wait for I/O events on an epoll file > > descriptor > > > > SYNOPSIS > > > > int epoll_mod_wait(int epfd, int flags, > > int ncmds, struct epoll_mod_cmd *cmds, > > struct epoll_wait_spec *spec); > > > > DESCRIPTION > > > > The epoll_mod_wait() system call can be seen as an enhanced combination > > of several epoll_ctl(2) calls, which are followed by an epoll_pwait(2) > > call. It is superior in two cases: > > > > 1) When epoll_ctl(2) are followed by epoll_wait(2), using epoll_mod_wait > > will save context switches between user mode and kernel mode; > > > > 2) When you need higher precision than microsecond for wait timeout. > > > > The epoll_ctl(2) operations are embedded into this call by with ncmds > > and cmds. The latter is an array of command structs: > > > > struct epoll_mod_cmd { > > > > /* Reserved flags for future extension, must be 0 for now. */ > > int flags; > > > > /* The same as epoll_ctl() op parameter. */ > > int op; > > > > /* The same as epoll_ctl() fd parameter. */ > > int fd; > > > > /* The same as the "events" field in struct epoll_event. */ > > uint32_t events; > > > > /* The same as the "data" field in struct epoll_event. */ > > uint64_t data; > > > > /* Output field, will be set to the return code once this > > * command is executed by kernel */ > > int error; > > }; > > I would add an extra u32 at the end so that the structure size will be > a multiple of 8 bytes on all platforms. *shrug*, but if you do so, enforce that it has a value of 0 or return -EINVAL, just like a flags field. Alternatively, move the last field earlier and make flags a uint64_t. - Josh Triplett