Re: [PATCH] test: Update README.md

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Sep 24, 2025 at 09:58:57AM +0800, Yumei Huang wrote:
> On Tue, Sep 23, 2025 at 6:32 PM Stefano Brivio <sbrivio@redhat.com> wrote:
> >
> > On Tue, 23 Sep 2025 14:36:41 +0800
> > Yumei Huang <yuhuang@redhat.com> wrote:
> >
> > > On Tue, Sep 23, 2025 at 4:03 AM Stefano Brivio <sbrivio@redhat.com> wrote:
> > > >
> > > > On Mon, 22 Sep 2025 11:03:23 +0800
> > > > Yumei Huang <yuhuang@redhat.com> wrote:
> > > >
> > > > > On Fri, Sep 19, 2025 at 5:58 PM Stefano Brivio <sbrivio@redhat.com> wrote:
> > > > > >
> > > > > > On Fri, 19 Sep 2025 09:43:29 +0800
> > > > > > Yumei Huang <yuhuang@redhat.com> wrote:
> > > > > >
> > > > > > > Signed-off-by: Yumei Huang <yuhuang@redhat.com>
> > > > > > > ---
> > > > > > >  test/README.md | 31 +++++++++++++++++++++++++++++--
> > > > > > >  1 file changed, 29 insertions(+), 2 deletions(-)
> > > > > > >
> > > > > > > diff --git a/test/README.md b/test/README.md
> > > > > > > index 91ca603..e3e9d37 100644
> > > > > > > --- a/test/README.md
> > > > > > > +++ b/test/README.md
> > > > > > > @@ -32,7 +32,7 @@ Example for Debian, and possibly most Debian-based distributions:
> > > > > > >      git go iperf3 isc-dhcp-common jq libgpgme-dev libseccomp-dev linux-cpupower
> > > > > > >      lm-sensors lz4 netavark netcat-openbsd psmisc qemu-efi-aarch64
> > > > > > >      qemu-system-arm qemu-system-misc qemu-system-ppc qemu-system-x86
> > > > > > > -    qemu-system-x86 sipcalc socat strace tmux uidmap valgrind
> > > > > > > +    sipcalc socat strace tmux uidmap valgrind
> > > > > > >
> > > > > > >  NOTE: the tests need a qemu version >= 7.2, or one that contains commit
> > > > > > >  13c6be96618c ("net: stream: add unix socket"): this change introduces support
> > > > > > > @@ -81,7 +81,12 @@ The following additional packages are commonly needed:
> > > > > > >
> > > > > > >  ## Regular test
> > > > > > >
> > > > > > > -Just issue:
> > > > > > > +Before running the tests, you need to prepare the required assets:
> > > > > > > +
> > > > > > > +    cd test
> > > > > > > +    make assets
> > > > > > > +
> > > > > > > +Then issue:
> > > > > > >
> > > > > > >      ./run
> > > > > > >
> > > > > > > @@ -91,6 +96,28 @@ variable settings: DEBUG=1 enables debugging messages, TRACE=1 enables tracing
> > > > > > >
> > > > > > >      PCAP=1 TRACE=1 ./run
> > > > > > >
> > > > > > > +**Note:**
> > > > > > > +
> > > > > > > +* It's recommended to run the commands as a non-root user.
> > > > > > > +  Due to [Bug 967509](https://bugzilla.redhat.com/show_bug.cgi?id=967509),
> > > > > > > +  if you switch users with `su` or `sudo`, the directory `/run/user/ID` may
> > > > > > > +  not be created. In that case, `XDG_RUNTIME_DIR` will incorrectly point to
> > > > > > > +  `/run/user/0` instead of `/run/user/ID`, which can cause error.
> > > > > >
> > > > > > Thanks for the research, I wasn't aware of that, and recently spent
> > > > > > quite some time figuring that out (for other reasons):
> > > > > >
> > > > > >   https://issues.redhat.com/browse/RHEL-70222
> > > > > >
> > > > > > in that case, XDG_RUNTIME_DIR was simply not set. Things were working
> > > > > > with 'machinectl shell' instead.
> > > > > >
> > > > > > At the same time: running this whole stuff as root sounds rather crazy,
> > > > > > unless it's a throw-away VMs with absolutely nothing important on it.
> > > > > >
> > > > > > That is, regardless of the issue with XDG_RUNTIME_DIR. I would maybe
> > > > > > make the wording stronger, something like:
> > > > > >
> > > > > > * Don't run the tests as root, it's not needed!
> > > > > > * If you really need to, note that ...
> > > > > >
> > > > > > > +  **Workaround:** Log out and log back in as the intended user to ensure the
> > > > > > > +  correct runtime directory is set up.
> > > > > >
> > > > > > We could also suggest 'machinectl shell' if it's really needed for
> > > > > > whatever reason.
> > > > >
> > > > > I'm not sure how 'machinectl shell' works here. The error happens when
> > > > > running 'make assets',
> > > > > which calls 'prepare-distro-img.sh' script, which calls 'virsh edit'.
> > > >
> > > > Ah, I didn't know! So this is actually similar to
> > > > https://issues.redhat.com/browse/RHEL-70222.
> > > >
> > > > > If we run 'make assets' with root, the error is like this:
> > > > >
> > > > > ./prepare-distro-img.sh prepared-debian-8.11.0-openstack-amd64.qcow2
> > > > > libguestfs: error: could not create appliance through libvirt.
> > > > > Original error from libvirt: Cannot access storage file
> > > > > '/home/test/passt/test/prepared-debian-8.11.0-openstack-amd64.qcow2'
> > > > > (as uid:107, gid:107): Permission denied [code=38 int1=13]
> > > > >
> > > > > If we switch to a non-root user via 'su', the error is like this:
> > > > >
> > > > > ./prepare-distro-img.sh prepared-debian-8.11.0-openstack-amd64.qcow2
> > > > > libvirt: XML-RPC error : Cannot create user runtime directory
> > > > > '/run/user/0/libvirt': Permission denied
> > > > > libguestfs: error: could not connect to libvirt (URI =
> > > > > qemu:///session): Cannot create user runtime directory
> > > > > '/run/user/0/libvirt': Permission denied [code=38 int1=13]
> > > > > make: *** [Makefile:115: prepared-debian-8.11.0-openstack-amd64.qcow2] Error 1
> > > > >
> > > > > Do you mean to run 'make assets' with 'machinectl shell'? What's the
> > > > > exact cmd here? I tried this, seems not work.
> > > > >
> > > > >     # machinectl shell --uid=$(id -u pat) .host
> > > > > /home/test/passt/test/make assets
> > > > >     Connected to the local host. Press ^] three times within 1s to exit session.
> > > > >
> > > > >     Connection to the local host terminated.
> > > >
> > > > No, I mean using 'machinectl shell' instead of 'su' (it's intended as a
> > > > replacement), that is:
> > > >
> > > >     $ machinectl shell
> > > >     # make assets
> > > >
> > > > ...because that one will set XDG_RUNTIME_DIR.
> > >
> > > Yes, 'machinectl shell' will solve the issue when switching to a
> > > non-root user via su. But it doesn't solve the issue when running
> > > 'make assets' as root. They are actually different issues as above.
> >
> > Can one need specify a XDG_RUNTIME_DIR that actually exists, maybe?
> > Does that work?
> 
> I guess I need to clarify the issues more clearly.
> 
> a) If we login the system with the non-root user, `/run/user/ID` is
> created and XDG_RUNTIME_DIR is pointing to that correctly. So 'make
> assets' works well.
> 
> b) If we login the system with root, then switch to a non-root user
> via 'su', 'make assets' fails due to Bug 967509. XDG_RUNTIME_DIR is
> not reset and points to /run/user/(ID of the previous user), which is
> /run/user/0.
> 
>     libguestfs: error: could not connect to libvirt (URI =
> qemu:///session): Cannot create user runtime directory
> '/run/user/0/libvirt': Permission denied [code=38 int1=13]
> 
> Switching the user with 'machinectl shell --uid=$user' can solve the issue.
> 
> c) If we run 'make assets' as root, (no matter we just login with
> root, or switch to root via su or machinectl shell), 'make assets'
> always fails with a different error.
> 
>     libguestfs: error: could not create appliance through libvirt.
> Original error from libvirt: Cannot access storage file
> '/home/pat/tmp/t5-passt/test/prepared-debian-10-nocloud-amd64.qcow2'
> (as uid:107, gid:107): Permission denied [code=38 int1=13]
> 
> The XDG_RUNTIME_DIR is no longer an issue, since root can access every
> directory under /run/user. I guess the problem here is that we just
> can't run 'virsh edit' as root.

I'm guessing the problem here is that something in the libguestfs -> libvirt
-> whatever chain is dropping capabilities, so it no longer has
permission to everything.  Or if the home directory there is mounted
via NFS or something, there can be root doesn't actually have
permission to everything.

> >
> > > Maybe we can just put it like:
> > >
> > >     Running the commands as root is just not allowed.  If you login
> > > the system with root, don't use su to switch users due to [Bug
> > > 967509](https://bugzilla.redhat.com/show_bug.cgi?id=967509). Log out
> > > and log back in as the intended user, or use 'machinectl shell
> > > --uid=$user'.
> > >
> > > What do you think?
> >
> > Well, it's free software, so "not allowed" doesn't really mean much.
> >
> > I would simply warn users that it's a bad idea and it's not needed,
> > something like my previous proposal:
> >
> >   * Don't run the tests as root, it's not needed!
> >   * If you really need to, note that ...
> >
> > and then just list the workaround that actually works.
> >
> > I think the most typical need for running things as root is that you
> > don't actually have other users (it happens with some VM images or
> > in embedded systems), so 'machinectl shell --uid=$user' won't really
> > help there.
> 
> Well, I have to admit that I usually do everything with root on my
> test machines. And I don't see a solution/workaround to fix the issue
> when running 'make assets' as root as c). The workaround proposed is
> just for those who login with root and switch to a non-root user to
> run the tests.

For many sorts of tests on throwaway machines, that's pretty
reasonable.  Testing passt we specifically want to test that it
operates as non-root, so I'd suggest you tweak your procedures for
grabbing a test machine so that you routinely create a user.

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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