Date: Fri, 7 Mar 2008 20:49:54 -0600 From: Damian Wiest <dwiest@vailsys.com> To: freebsd-geom@freebsd.org Subject: Re: geom_vinum platform-independent brokenness Message-ID: <20080308024954.GF15859@dfwdamian.vail> In-Reply-To: <20080307230058.GA8902@keira.kiwi-computer.com> References: <20080307230058.GA8902@keira.kiwi-computer.com>
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On Fri, Mar 07, 2008 at 05:00:58PM -0600, Rick C. Petty wrote:
> Since no one seems to be working on fixing gvinum, I've decided to
> investigate and address some problems I have encountered recently.
>
> ***
>
> There is an incompatibility in geom_vinum with respect to i386/amd64.
> In particular, the following structure (in geom_vinum_var.h) is stored
> as-is on each disk (or provider):
>
> struct gv_hdr {
> uint64_t magic;
> #define GV_MAGIC 22322600044678729LL
> #define GV_NOMAGIC 22322600044678990LL
>
> int config_length;
> struct gv_label label;
> };
>
> The problem is the "struct gv_label" is not aligned properly against the
> int. On i386 and amd64 system, this corresponds to these offsets:
>
> i386 amd64 field
> ---- ----- -----
> 0 0 magic
> 8 8 config_length
> - - from struct gv_label :
> 12 16 sysname
> 44 48 name (of drive)
> 76 80 date_of_birth
> 84 96 last_update
> 92 112 drive_size
> = =
> 100 120 = total header size
>
> Because of this, someone who has volumes created with i386 gvinum cannot
> put those volumes onto an amd64 system, and vice-versa!
So you're saying that you should be able to remove a disk (or set of disks)
from an x86 system, install it in a system running the amd64 release and
have things just work? I would imagine that most people would simply use
dump/restore, but I agree that it would be nice if one didn't have to do
this.
How is this scenario handled for basic disks? Can an amd64 system
handle a disk that was labeled on an x86 system? I haven't ever tried
this, but the manpage for bsdlabel suggests that it won't work unless
you originally wrote an amd64 label by using the -m option.
Aren't you going to run into issues with your filesystems when moving
from one architecture to another that uses a different bus width?
-Damian
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