Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753512Ab2K2Nhv (ORCPT ); Thu, 29 Nov 2012 08:37:51 -0500 Received: from mail-ia0-f174.google.com ([209.85.210.174]:42009 "EHLO mail-ia0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751155Ab2K2Nhu (ORCPT ); Thu, 29 Nov 2012 08:37:50 -0500 MIME-Version: 1.0 Reply-To: mtk.manpages@gmail.com In-Reply-To: References: <1336004953.4240.9.camel@mop> <1354125084.20578.1.camel@nja> From: "Michael Kerrisk (man-pages)" Date: Thu, 29 Nov 2012 14:37:29 +0100 Message-ID: Subject: Re: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length record buffer To: Kay Sievers Cc: Linus Torvalds , Greg Kroah-Hartmann , Ingo Molnar , Linux Kernel Mailing List Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5405 Lines: 177 On Thu, Nov 29, 2012 at 2:28 PM, Kay Sievers wrote: > On Thu, Nov 29, 2012 at 2:18 PM, Michael Kerrisk (man-pages) > wrote: >> On Wed, Nov 28, 2012 at 6:51 PM, Kay Sievers wrote: > >>> Before: >>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 286965 >>> syslog(SYSLOG_ACTION_READ_CLEAR, "<12>"..., 1000000) = 24000 >>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 286965 >>> >>> After: >>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 90402 >>> syslog(SYSLOG_ACTION_READ_CLEAR, "<5>"..., 1000000) = 90402 >>> syslog(SYSLOG_ACTION_SIZE_UNREAD, 0, 0) = 0 > >> I'm going to call my report yesterday bogus. Somewhere along the way, >> I got confused while testing something, and my statement about 2.6.31 >> behavior is wrong: the 2.6.31 and 3.5 behaviors are the same. As such, >> your patch is unneeded. Sorry for wasting your time. > > I think you have been right with your report. The above pasted > before/after from the patch commit text is actually a result of real > testing with current git. And your initial description sounds right, > and the patch seems to produce the expected results here. I just > confused the numbers in your report and wrongly parsed 2.6 > 3.6. > > Hmm, at least do far we did not blame anybody else than ourselves as > confused. One of us at least is right, and it looks you have been, and > I also think the patch is at least intended to be right. :) Okay -- I'm pretty sure I am right about being wrong ;-). Could you do some comparative testing please between 3.5 and pre-3.5. I have a little test program below. When I rechecked 2.6.31 and 3.5 using this program I found the behavior was the same, which is why I conclude my report is wrong. (And also, your proposed patch in response to my bogus report produces different behavior from 2.6.31). Thanks, Michael /*#* t_klogctl.c klogctl(3) is the glibc interface for syslog(2) */ #include #include #include #include #include #include #include #define errMsg(msg) do { perror(msg); } while (0) #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \ } while (0) #define fatal(msg) do { fprintf(stderr, "%s\n", msg); \ exit(EXIT_FAILURE); } while (0) /* Close the log. Currently a NOP. */ #define SYSLOG_ACTION_CLOSE 0 /* Open the log. Currently a NOP. */ #define SYSLOG_ACTION_OPEN 1 /* Read from the log. */ #define SYSLOG_ACTION_READ 2 /* Read all messages remaining in the ring buffer. */ #define SYSLOG_ACTION_READ_ALL 3 /* Read and clear all messages remaining in the ring buffer */ #define SYSLOG_ACTION_READ_CLEAR 4 /* Clear ring buffer. */ #define SYSLOG_ACTION_CLEAR 5 /* Disable printk's to console */ #define SYSLOG_ACTION_CONSOLE_OFF 6 /* Enable printk's to console */ #define SYSLOG_ACTION_CONSOLE_ON 7 /* Set level of messages printed to console */ #define SYSLOG_ACTION_CONSOLE_LEVEL 8 /* Return number of unread characters in the log buffer */ #define SYSLOG_ACTION_SIZE_UNREAD 9 /* Return size of the log buffer */ #define SYSLOG_ACTION_SIZE_BUFFER 10 int main(int argc, char *argv[]) { int s; #define BSIZE 500000 char buf[BSIZE]; if (argc < 2) { fprintf(stderr, "Usage: %s command-num [arg]\n", argv[0]); exit(EXIT_FAILURE); } int cmd; cmd = atoi(argv[1]); switch (cmd) { case SYSLOG_ACTION_READ: /* 2 */ printf("SYSLOG_ACTION_READ\n"); s = klogctl(SYSLOG_ACTION_READ, buf, (argc > 2) ? atoi(argv[2]) : BSIZE); if (s == -1) errExit("klogctl-READ"); printf("Return value: %d\n", s); if (write(2, buf, s) != s) errMsg("write"); break; case SYSLOG_ACTION_READ_ALL: /* 3 */ case SYSLOG_ACTION_READ_CLEAR: /* 4 */ if (cmd == SYSLOG_ACTION_READ_CLEAR) printf("SYSLOG_ACTION_READ_CLEAR\n"); else printf("SYSLOG_ACTION_READ_ALL\n"); s = klogctl(cmd, buf, (argc > 2) ? atoi(argv[2]) : BSIZE); if (s == -1) errExit("klogctl-READ_ALL/READ_CLEAR"); printf("Return value: %d\n", s); if (write(2, buf, s) != s) errMsg("write"); if (cmd == SYSLOG_ACTION_READ_CLEAR) printf("Ring buffer cleared\n"); break; case SYSLOG_ACTION_CLEAR: /* 5 */ printf("SYSLOG_ACTION_CLEAR\n"); s = klogctl(SYSLOG_ACTION_CLEAR, NULL, 0); if (s == -1) errExit("klogctl-CLEAR"); printf("Return value: %d\n", s); printf("Ring buffer cleared\n"); break; case SYSLOG_ACTION_SIZE_UNREAD: /* 9 */ printf("SYSLOG_ACTION_SIZE_UNREAD\n"); s = klogctl(SYSLOG_ACTION_SIZE_UNREAD, NULL, 0); if (s == -1) errExit("klogctl-SIZE_UNREAD"); printf("Number of unread bytes: %d\n", s); break; case SYSLOG_ACTION_SIZE_BUFFER: /* 10 */ printf("SYSLOG_ACTION_SIZE_BUFFER\n"); s = klogctl(SYSLOG_ACTION_SIZE_BUFFER, NULL, 0); if (s == -1) errExit("klogctl-SIZE_BUFFER"); printf("Size of buffer: %d\n", s); break; default: fatal("Bad command"); break; } exit(EXIT_SUCCESS); } -- 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/