[Xen-devel] Re: POC: ncurses in stubdom

[Ferenc Wagner <wferi@xxxxxxx>]

Samuel Thibault <samuel.thibault@xxxxxxxxxxxx> writes:

> Ferenc Wagner, le Tue 28 Apr 2009 21:56:07 +0200, a Ãcrit :
>
>> But then trying the operation itself provides the exact same
>> diagnostics.  This is what I mean by "pointless".
>
> Ok, but applications could still be upset to see access() work and not
> open(), or vice-versa.

Sure, but then they are buggy.  No one should assume that nothing
changes in the time slice between access() and open() for example.

>> #if defined(HAVE_POSIX_MEMALIGN)
>>   if (posix_memalign (&p, align, size) != 0)
>>     p = 0;
>> #elif defined(HAVE_MEMALIGN)
>>   p = memalign (align, size);
>
> Errr, so grub2 doesn't unconditionally use posix_memalign.  How did
> grub2 detect HAVE_POSIX_MEMALIGN?

By autoconf:
AC_CHECK_FUNCS(posix_memalign memalign asprintf)

> Adding posix_memalign as a proper function shouldn't be hard, though
> (and could be submitted upstream).

If you say so...  It's actually the first time I met the memalign
family.

>>> Just take that implementation and it will get compiled in.
>> 
>> Sorry for sounding dense...  How do I "take that implementation"?  I
>> guess you don't mean cut&paste, do you?
>
> Yep.

Horrors!

>>>>> Now, I'm wondering about the ncurses requirement: is grub2 really
>>>>> using it for the bootloader, not just for the userland tool?
>>>> 
>>>> No, it does not require it for the bootloader.  My plan is to port the
>>>> grub-emu userland tool instead, and finally patch kexec on that, just
>>>> like you did with grub1.
>>>
>>> Err, I didn't port the userland tool, I ported the bootloader.  The
>>> userland grub1 tool does not even include code to boot kernels,
>>> actually...
>> 
>> Yes, it's all the same for grub2.
>
> Err, does grub2 compiles ncurses into the bootloader too?

No, it does not.

>> but neither is applicable to c-stubdom, where the Makefile stops at
>> creating an archive.  I can't add -lncurses there...  And generally I
>> feel like being on a totally wrong track, as this part doesn't seem to
>> involve minios at all.
>
> Oh right, sorry.  The final link is not done there but by the minios
> paragraph of stubdom/Makefile.  You can either set APP_LDLIBS to
> -lncurses there, to override the empty default of mini-os/Makefile, or
> add -lncurses to APP_LDLIBS in the ifeq($libc),y) section along others.

This is what I did in the POC.

> Ferenc Wagner, le Tue 28 Apr 2009 22:02:03 +0200, a Ãcrit :
>
>> Eventually it could as well read the terminfo database from the host.
>> Btw. it tries to do so by invoking a stat() call, and then segfaults
>> the stubdom.  So there's some problem left here, more serious than
>> access().
>
> Right, I'm not sure we really want to have a stubdom do this.

Do you mean accessing the host filesystem?  I agree that shouldn't be
made necessary, as stubdoms are a security measure in part.

Huh, I'm getting out of steam for today, and not sure I will be able
to work on this tomorrow.  Now comes interfacing grub2's host disk
access code with blkfront, which wouldn't be hard if blkfront didn't
require aligned buffers... :/
-- 
Thanks for today's help, again!
Cheers,
Feri.

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