Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751231AbXBOB3A (ORCPT ); Wed, 14 Feb 2007 20:29:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751482AbXBOB3A (ORCPT ); Wed, 14 Feb 2007 20:29:00 -0500 Received: from x35.xmailserver.org ([64.71.152.41]:3910 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751231AbXBOB27 (ORCPT ); Wed, 14 Feb 2007 20:28:59 -0500 X-AuthUser: davidel@xmailserver.org Date: Wed, 14 Feb 2007 17:28:56 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Ingo Molnar cc: Alan , Linus Torvalds , Linux Kernel Mailing List , Arjan van de Ven , Christoph Hellwig , Andrew Morton , Ulrich Drepper , Zach Brown , Evgeniy Polyakov , "David S. Miller" , Benjamin LaHaise , Suparna Bhattacharya , Thomas Gleixner Subject: Re: [patch 05/11] syslets: core code In-Reply-To: Message-ID: References: <20070213142035.GF638@elte.hu> <20070214210251.GA15025@elte.hu> <20070214215613.56d76257@localhost.localdomain> <20070214223216.GA7616@elte.hu> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3711 Lines: 108 On Wed, 14 Feb 2007, Davide Libenzi wrote: > On Wed, 14 Feb 2007, Ingo Molnar wrote: > > > yeah, that's another key thing. I do plan to provide a sys_upcall() > > syscall as well which calls a 5-parameter user-space function with a > > special stack. (it's like a lightweight signal/event handler, without > > any of the signal handler legacies and overhead - it's like a reverse > > system call - a "user call". Obviously pure userspace would never use > > sys_upcall(), unless as an act of sheer masochism.) > > That is exactly what I described as clets. Instead of having complex jump > and condition interpreters on the kernel (on top of new syscalls to > modify/increment userspace variables), you just code it in C and you pass > the clet pointer to the kernel. > The upcall will setup a frame, execute the clet (where jump/conditions and > userspace variable changes happen in machine code - gcc is pretty good in > taking care of that for us) on its return, come back through a > sys_async_return, and go back to userspace. So, for example, this is the setup code for the current API (and that's a really simple one - immagine going wacko with loops and userspace varaible changes): static struct req *alloc_req(void) { /* * Constants can be picked up by syslets via static variables: */ static long O_RDONLY_var = O_RDONLY; static long FILE_BUF_SIZE_var = FILE_BUF_SIZE; struct req *req; if (freelist) { req = freelist; freelist = freelist->next_free; req->next_free = NULL; return req; } req = calloc(1, sizeof(struct req)); /* * This is the first atom in the syslet, it opens the file: * * req->fd = open(req->filename, O_RDONLY); * * It is linked to the next read() atom. */ req->filename_p = req->filename; init_atom(req, &req->open_file, __NR_sys_open, &req->filename_p, &O_RDONLY_var, NULL, NULL, NULL, NULL, &req->fd, SYSLET_STOP_ON_NEGATIVE, &req->read_file); /* * This second read() atom is linked back to itself, it skips to * the next one on stop: */ req->file_buf_ptr = req->file_buf; init_atom(req, &req->read_file, __NR_sys_read, &req->fd, &req->file_buf_ptr, &FILE_BUF_SIZE_var, NULL, NULL, NULL, NULL, SYSLET_STOP_ON_NON_POSITIVE | SYSLET_SKIP_TO_NEXT_ON_STOP, &req->read_file); /* * This close() atom has NULL as next, this finishes the syslet: */ init_atom(req, &req->close_file, __NR_sys_close, &req->fd, NULL, NULL, NULL, NULL, NULL, NULL, 0, NULL); return req; } Here's how your clet would look like: static long main_sync_loop(ctx *c) { int fd; char file_buf[FILE_BUF_SIZE+1]; if ((fd = open(c->filename, O_RDONLY)) == -1) return -1; while (read(fd, file_buf, FILE_BUF_SIZE) > 0) ; close(fd); return 0; } Kinda easier to code isn't it? And the cost of the upcall to schedule the clet is widely amortized by the multple syscalls you're going to do inside your clet. - Davide - 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/