Re: sbuild on hurd-amd64...

Johannes Schauer Marin Rodrigues, le sam. 06 sept. 2025 13:38:17 +0200, a ecrit:
> Quoting Samuel Thibault (2025-09-06 07:52:42)
> > Johannes Schauer Marin Rodrigues, le sam. 06 sept. 2025 03:08:50 +0200, a ecrit:
> > > > > Also, can we tell mmdebstrap to use the normal chroot instead of
> > > > > fakechroot? chroot() is not a privileged operation in the Hurd.
> > > > Oh, I wasn't aware of that!
> > > 
> > > Yes. If you have privileges to chroot(), you can just use --mode=root.
> > 
> > But currently none of the expected ways work as non-root:
> > 
> > $ mmdebstrap --mode=root --variant=required --keyring=/usr/share/keyrings/debian-ports-archive-keyring.gpg '' foo.tar.gz 'deb http://deb.debian.org/debian-ports unreleased main' 'deb http://deb.debian.org/debian-ports/ unstable main'
> > E: need to be root
> 
> Would/should the above work as the non-root user on hurd?

Well, I don't know the exact intention of --mode=root :)

What I was understanding is that it is a mode that uses an actual root
uid, not faking root.

But I also read that it uses chroot, which is what we'd want to use on
the Hurd, but along with an additionnal fakeroot-hurd, which would
rather be the fakeroot mode.

> > with additionnal fakeroot-hurd:
> > $ fakeroot-hurd mmdebstrap --mode=root --variant=required --keyring=/usr/share/keyrings/debian-ports-archive-keyring.gpg '' foo.tar.gz 'deb http://deb.debian.org/debian-ports unreleased main' 'deb http://deb.debian.org/debian-ports/ unstable main' 
> > Undefined subroutine &main::SYS_capget called at /usr/bin/mmdebstrap line 6081.
> > /bin/fakeauth: Error 255 for child 23498
> > /bin/settrans: Error 255 for child 23497
> 
> This is because in Linux it is possible to be uid 0 but still not be able to
> mount anything. The above uses the capget and later the prctl syscalls to
> figure out whether mounting is possible or not.
> 
> We can do multiple things here:
> 
>  * it seems there is no capget on hurd, so mmdebstrap should not even attempt
>    this codepath on hurd

Yes.

>  * instead, maybe a different check can/should be performed on hurd but i
>    don't know enough hurd to implement this

I don't think there is any check need: you can always mount something
the hurd. The translator will run under the user identity, simply.

> > $ mmdebstrap --mode=fakeroot --variant=required --keyring=/usr/share/keyrings/debian-ports-archive-keyring.gpg '' foo.tar.gz 'deb http://deb.debian.org/debian-ports unreleased main' 'deb http://deb.debian.org/debian-ports/ unstable main' 
> > E: need working fakechroot binary
> > 
> > on GNU/Hurd it should be using chroot instead of using the fragile
> > fakechroot. I had tried to create a hurdish fakechroot that just calls
> > chroot(), but apparently mmdebstrap is expecting various fakechroot
> > environment variables, I didn't easily manage to find out what.
> 
> Instead of you creating a fakechroot for hurd which is close enough to the
> fakechroot on linux, lets instead fix mmdebstrap to do the right thing on
> hurd out-of-the-box. I'll gladly accept patches!

I don't really know where one would tell mmdebstrap to just use chroot.

> I can easily implement the --skip=... options mentioned above but I'll need
> help with adding hurd-specific things.

I don't think there is really much hurd-specific. Really I believe it's
just about calling fakeroot-hurd and chroot, just like you would use
fakeroot + chroot on linux.

Samuel