svn commit: r322969 - in head: sbin/mdconfig sys/dev/md sys/sys
Maxim Sobolev
sobomax at freebsd.org
Tue Aug 29 19:11:09 UTC 2017
Ian, yes, you are right, there appears to be md_ioctl wrapper in the
FREEBSD32 layer, which I've completely missed it turns out. I add the label
support into that as well. Thanks for bringing it up, I'll follow-up with
the patch to make 32-bit code fully functional WRT labels. It's not broken
at the moment but the label is not going to be visible to the 32-bit
version of the mdconfig(8) running on 64-bit kernels.
-Max
On Tue, Aug 29, 2017 at 7:19 AM, Ian Lepore <ian at freebsd.org> wrote:
> 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 <jhb at 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 at 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 <jhb at 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
> > >
> > >
>
>
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