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 <j...@freebsd.org> > wrote: > > > > > On Monday, August 28, 2017 12:46:48 PM Ryan Libby wrote: > > > > > > On Mon, Aug 28, 2017 at 11:24 AM, Maxim Sobolev <sobomax@freebsd. > > > 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 <j...@freebsd.org> > > > > 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 > > > > _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
