Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754699Ab2K2OS6 (ORCPT ); Thu, 29 Nov 2012 09:18:58 -0500 Received: from mail-ie0-f174.google.com ([209.85.223.174]:46962 "EHLO mail-ie0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754562Ab2K2OSz (ORCPT ); Thu, 29 Nov 2012 09:18:55 -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 15:18:34 +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: 3220 Lines: 69 On Thu, Nov 29, 2012 at 3:08 PM, Kay Sievers wrote: > On Thu, Nov 29, 2012 at 2:37 PM, Michael Kerrisk (man-pages) > wrote: >> 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). > > Oh, seems you are right. > > The old kernel does not return 0, while it probably should. The > current kernel seems to do the same thing. > > But the behaviour with the patch stills seems like the better and the > obvious and expected behaviour to me. :) The point here I think is that the semantics of the various syslog() commands are surprising, which is what led me into some confusion in testing. Essentially, command 5 ("clear ring buffer") does not really clear anything, it simply sets bookkeeping variables that affect the behavior of commands 3 and 4. Of particular note is that command 5 does NOT affect commands 2 and 9, and command 9 is only returning the number of bytes that would be read by command 2. The man page could do with some improvement (and will get it). So, just to be clear: you better not apply your patch; it might break something ;-). Cheers, Michael -- 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/