[xen-tools] Re: some ubuntu machines may need libc6-xen installed in bootstrap...

[Andrew Sutherland]

Steve Kemp wrote:
>   That isn't good!  Do you have any idea why this fails?  An strace
>  or similar might help track it down...

Okay, so this does in fact, turn out to be weird.  I have attached a
reduced strace.  Basically, it looks like the 'preinst' file is being
executed (pid 16424) and it invokes "touch /etc/ld.so.nohwcap" (pid
16425) which implodes for reasons that aren't entirely clear to me.

In a nutshell, touch.c in coreutils calls its library function futimens.
 futimens calls the glibc 'futimesat' which defers to the glibc
'futimes' call.  Because that call uses /proc/self which the chroot
apparently does not provide,  it should return ENOSYS and coreutils'
'futimens' should fall back to using the syscall 'utimes' with the
filename passed in on the command line.  Even if the filename pointer
was gibberish, the process still shouldn't segfault unless the
successful open of the file (which is relevant to ld.so) somehow impacts
the dynamic loader's behavior at that point.

I must confess I hadn't thought too much about this problem originally,
and for whatever misguided reason thought this stage was happening in a
Xen VM rather than a chroot.  In that case, it made sense that there was
a glibc TLS problem that cramming the package in before VM-time fixed.
As it stands, I'm puzzled, but not quite puzzled enough to want to do
the legwork required to run this problem to ground.

>   Off the top of my head I'm not sure why you need to specify "main",
>  "universe", etc.  It should be sufficient to just have a package
>  blacklist - but maybe I'm being dense...

libc6-xen is part of 'universe', whereas debootstrap only includes
'main' by default.  When universe is not included, it fails to locate my
explicitly included libc6-xen and gives up.

Andrew
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