From owner-svn-src-head@freebsd.org Tue Aug 29 14:19:33 2017 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 3CC8ADDC4CD for ; Tue, 29 Aug 2017 14:19:33 +0000 (UTC) (envelope-from ian@freebsd.org) Received: from outbound1b.ore.mailhop.org (outbound1b.ore.mailhop.org [54.200.247.200]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 1D26F639BB for ; Tue, 29 Aug 2017 14:19:32 +0000 (UTC) (envelope-from ian@freebsd.org) X-MHO-User: 145cec00-8cc5-11e7-950d-03a3531dacf2 X-Report-Abuse-To: https://support.duocircle.com/support/solutions/articles/5000540958-duocircle-standard-smtp-abuse-information X-Originating-IP: 73.78.92.27 X-Mail-Handler: DuoCircle Outbound SMTP Received: from ilsoft.org (unknown [73.78.92.27]) by outbound1.ore.mailhop.org (Halon) with ESMTPSA id 145cec00-8cc5-11e7-950d-03a3531dacf2; Tue, 29 Aug 2017 14:19:34 +0000 (UTC) Received: from rev (rev [172.22.42.240]) by ilsoft.org (8.15.2/8.15.2) with ESMTP id v7TEJN7b001354; Tue, 29 Aug 2017 08:19:23 -0600 (MDT) (envelope-from ian@freebsd.org) Message-ID: <1504016363.56799.71.camel@freebsd.org> Subject: Re: svn commit: r322969 - in head: sbin/mdconfig sys/dev/md sys/sys From: Ian Lepore To: Maxim Sobolev , John Baldwin Cc: Ryan Libby , svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers Date: Tue, 29 Aug 2017 08:19:23 -0600 In-Reply-To: References: <201708281554.v7SFs8fr014268@repo.freebsd.org> <2937323.CvTEtZnL2T@ralph.baldwin.cx> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.18.5.1 FreeBSD GNOME Team Port Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.23 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: Tue, 29 Aug 2017 14:19:33 -0000 On Mon, 2017-08-28 at 16:40 -0700, Maxim Sobolev wrote: > John, well, this depends on how you look at it. The padding element size is > "int", which when you account for the alignment has the nice property on > both 32 and 64-bit arches that no matter what kind of element you add > (char, short, int or void *), you only need to bring down MDNPAD by 1 to > keep the structure size the same. It also has a second interesting property > that number of padding elements needed stays the same no matter if > sizeof(void *) is 64 or 32, otherwise you would have to have MDNPAD diverge > on 32 and 64 bit arches after adding pointer which has different sizes > (just like you suggested it should originally). I am not 100% sure if it > was intentionally designed like this by PHK from the day one, but I found > it quite interesting. I am not quite sure if having sizeof(md_ioctl) is > ever been required to stay the same between 64 and 32 bit arches. I don't > think there is any support for having 32-bit mdconfig run on 64-bit kernel. > > -Max > mdconfig works in 32-bit jails on a 64-bit host, and I rely on that being the case.  With poudriere evolving to become a general image building tool, and with it being so jail-centric, it's likely to be another use case. -- Ian > On Mon, Aug 28, 2017 at 1:49 PM, John Baldwin > wrote: > > > > > On Monday, August 28, 2017 12:46:48 PM Ryan Libby wrote: > > > > > > On Mon, Aug 28, 2017 at 11:24 AM, Maxim Sobolev > > org> > > wrote: > > > > > > > > > > > Hi John, > > > > > > > > Thanks for your feedback! To address the points that you've > > > > raised: > > > > > > > > 1. I've tested on both 32 and 64 bit platforms, it seems not to > > > > be the > > > > case. See imp's comment and my reply here > > > > https://reviews.freebsd.org/D10457#216855 . Did I miss > > > > something? Can > > you > > > > > > > > > > > post piece of C code that produces different sizeof(struct old) > > > > vs. > > > > sizeof(struct new) on some platform? > > > [...] > > > > > > > > On Mon, Aug 28, 2017 at 9:19 AM, John Baldwin > > > > wrote: > > > > > > > > > > > > > > On Monday, August 28, 2017 03:54:08 PM Maxim Sobolev wrote: > > > > > > > > > > > > Author: sobomax > > > > > > Date: Mon Aug 28 15:54:07 2017 > > > > > > New Revision: 322969 > > > > > > URL: https://svnweb.freebsd.org/changeset/base/322969 > > > > > > > > > > > > Log: > > > > > >   Add ability to label md(4) devices. > > > > > > > > > > > >   This feature comes from the fact that we rely memory- > > > > > > backed md(4) > > > > > >   in our build process heavily. However, if the build goes > > > > > > haywire > > > > > >   the allocated resources (i.e. swap and memory-backed > > > > > > md(4)'s) need > > > > > >   to be purged. It is extremely useful to have ability to > > > > > > attach > > > > > >   arbitrary labels to each of the virtual disks so that > > > > > > they can > > > > > >   be identified and GC'ed if neecessary. > > > > > > > > > > > >   MFC after:  4 weeks > > > > > >   Differential Revision:      https://reviews.freebsd.org/D > > > > > > 10457 > > > > > > > > > > > > Modified: > > > > > >   head/sbin/mdconfig/mdconfig.8 > > > > > >   head/sbin/mdconfig/mdconfig.c > > > > > >   head/sys/dev/md/md.c > > > > > >   head/sys/sys/mdioctl.h > > > > > > > > > > > > Modified: head/sys/sys/mdioctl.h > > > > > > =========================================================== > > > > > > = > > > > > ================== > > > > > > > > > > > > --- head/sys/sys/mdioctl.h    Mon Aug 28 14:49:26 2017 > > (r322968) > > > > > > > > > > > > > > > > > > > > > > > > +++ head/sys/sys/mdioctl.h    Mon Aug 28 15:54:07 2017 > > (r322969) > > > > > > > > > > > > > > > > > > > > > > > > @@ -49,7 +49,7 @@ enum md_types {MD_MALLOC, MD_PRELOAD, > > > > > > MD_VNODE, > > MD_SWA > > > > > > > > > > > > > > > > > > > > > > > >   * Ioctl definitions for memory disk pseudo-device. > > > > > >   */ > > > > > > > > > > > > -#define MDNPAD               97 > > > > > > +#define MDNPAD               96 > > > > > >  struct md_ioctl { > > > > > >       unsigned        md_version;     /* Structure layout > > > > > > version */ > > > > > >       unsigned        md_unit;        /* unit number */ > > > > > > @@ -61,6 +61,7 @@ struct md_ioctl { > > > > > >       u_int64_t       md_base;        /* base address */ > > > > > >       int             md_fwheads;     /* firmware heads */ > > > > > >       int             md_fwsectors;   /* firmware sectors > > > > > > */ > > > > > > +     char            *md_label;      /* label of the > > > > > > device */ > > > > > >       int             md_pad[MDNPAD]; /* padding for future > > > > > > ideas */ > > > > > >  }; > > > > > This isn't correct on 64-bit platforms.  MDNPAD needs to be > > > > > 95 on > > those > > > > > > > > > > > > > > > > > platforms. > > > [...] > > > > > > Can you report sizeof(md_ioctl) before and after for 32-bit and > > > 64-bit? > > > I think it may be: > > > 32-bit before: 440 > > > 32-bit after:  440 > > > 64-bit before: 448 > > > 64-bit after:  448 > > > > > > In other words, it looks like it used to produce different sizes > > > on the > > > different architectures, and still does.  It also looks like 32- > > > bit > > > before and after and 64-bit before included some undeclared > > > padding > > > after md_pad, so that this would fail: > > > CTASSERT(sizeof(md_ioctl) == offsetof(struct md_ioctl, md_pad) + > > >     sizeof(((struct md_ioctl *)NULL)->md_pad)); > > Ugh, yes.  To me that means that MDNPAD is actually wrong and > > should be > > fixed to account for the implicit padding.  That probably would > > result in > > requiring separate values for MDNPAD.  The current change as-is > > certainly > > looks wrong (and would be wrong if the padding were accurate) so it > > needs > > to be fixed to reflect reality. > > > > -- > > John Baldwin > > > >