From owner-svn-src-head@FreeBSD.ORG Fri Mar 13 17:25:00 2015 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id C4CD1DEC; Fri, 13 Mar 2015 17:25:00 +0000 (UTC) Received: from bigwig.baldwin.cx (bigwig.baldwin.cx [IPv6:2001:470:1f11:75::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 999808B8; Fri, 13 Mar 2015 17:25:00 +0000 (UTC) Received: from ralph.baldwin.cx (pool-173-54-116-245.nwrknj.fios.verizon.net [173.54.116.245]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 82BCFB91F; Fri, 13 Mar 2015 13:24:58 -0400 (EDT) From: John Baldwin To: Ian Lepore Subject: Re: svn commit: r279932 - head/sys/vm Date: Fri, 13 Mar 2015 13:19 -0400 Message-ID: <3013452.2FfDYxpIKo@ralph.baldwin.cx> User-Agent: KMail/4.14.2 (FreeBSD/10.1-STABLE; KDE/4.14.2; amd64; ; ) In-Reply-To: <1426263267.91779.19.camel@freebsd.org> References: <201503121806.t2CI6VSU034853@svn.freebsd.org> <29142844.yUiOLJLpmU@ralph.baldwin.cx> <1426263267.91779.19.camel@freebsd.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.7 (bigwig.baldwin.cx); Fri, 13 Mar 2015 13:24:58 -0400 (EDT) Cc: "svn-src-head@freebsd.org" , "svn-src-all@freebsd.org" , "src-committers@freebsd.org" , Ryan Stone X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 13 Mar 2015 17:25:01 -0000 On Friday, March 13, 2015 10:14:27 AM Ian Lepore wrote: > On Fri, 2015-03-13 at 06:24 -0400, John Baldwin wrote: > > On Thursday, March 12, 2015 05:24:51 PM Ian Lepore wrote: > > > On Thu, 2015-03-12 at 17:02 -0400, Ryan Stone wrote: > > > > On Thu, Mar 12, 2015 at 2:06 PM, Ian Lepore wrote: > > > > > > > > > Nullterminate strings returned via sysctl. > > > > > > > > > > PR: 195668 > > > > > > > > > > > > > To quote the manpage: > > > > > > > > > The *sbuf* family of functions allows one to safely > > > > > allocate, construct and release bounded null-terminated > > > > > strings in kernel space. > > > > > > > > IMO the sbuf API is broken if we have to explicitly null-terminate the > > > > string ourselves. > > > > > > If we want the nullterm to be counted in the length of data in the > > > buffer (and thus get transmitted back across the syscall boundary) we > > > need to put an explicit counted nullterm byte into the buffer. > > > > > > I had started down the path of making that (counting the nullterm byte > > > as part of the data in the buffer) a feature of sbuf that you could set > > > with a flag, but then whoever added sbuf_new_for_sysctl() didn't > > > propagate the flags field through the new function and I decided to not > > > go off into the weeds making a new flavor of that takes flags. > > > > One suggestion would be to consider using '\0' for a nul character instead of > > a bare 0. To me that communicates the intention more clearly to the reader. > > (One of the things I did not like about C++ < C++11 was the use of 0 for > > NULL. I much prefer nullptr and NULL in C over bare 0's for pointers for > > similar clarity reasons.) > > > > I have waffled back and forth between preferring 0 or '\0' for 30 years, > I just seem to go through phases with nullterm expression. > > In general I'm glad I got called away to an onsite meeting yesterday and > didn't get far with these changes, because the more I think about it, > the less satisfied I am with this expedient fix. The other fix I > started on, where a new SBUF_COUNTNUL flag can be set to inform the > sbuf_finish() code that you want the terminating nul counted in the data > length just feels like a better fit for the overall "automaticness" of > how the sbuf stuff works. Hmm, I actually think that it's a bug that the terminating nul isn't included when draining. If we fixed that then I think that fixes most of these? The places that explicitly use 'sysctl_handle_string()' with an sbuf should probably just be using sbuf_len(sb) + 1' explicitly. (Another option would be to have a sysctl_handle_sbuf() that was a wrapper around sysctl_handle_string() that included the + 1 to hide that detail if there is more than one.) -- John Baldwin