Re: [PATCH] test/cxl-xor-region.sh: remove redundant waitting

[Dan Williams <dan.j.williams@intel.com>]

Marc Herbert wrote:
> On 2025-05-16 17:23, dan.j.williams@intel.com wrote:
> 
> > 
> > So the assumption is that interfactive invocation of cxl commands should
> > arrange for a stablized snaphshot of the topology state.
> > 
> >> Now I am facing a problem that cxl command takes a long time to complete
> >> when I run it in a udev rule(do some configuration when CXL memdev is
> >> added).  I found it is caused by this function: waitting for udev
> >> queue's endding but itself is in the queue.  The cxl_wait_probe()
> >> function does not seem to allow me to do that.
> > 
> > Yes, that is a problem.
> > 
> >> So, the 2nd question is: is it against the spec to run cxl command in
> >> a udev rule?
> > 
> > No we need to find a way to make that work, so I consider this a bug
> > report. My initial reaction is that when called from a udev rule cxl-cli
> > should honor a new environment variable, perhaps "UDEV_CXL", that
> > disables this waiting that is only meant for human interactive mode.
> > 
> 
> If the distinction between two such "modes" is indeed desired, I don't
> think the name should point at the first known use case (UDEV) for
> it. For instance, you could also imagine that while some parts of test
> code want the current, blocking and "stabilized" behavior, other parts
> of some (other) test code want the currently missing), "fast" and
> unstable information without waiting. There could be other use cases, so
> in general the user interface (if any) should describe what it does, not
> who it is for.

This can be a surgical UDEV specific environment option for now because
there are no other use cases identified. The command line arguments can
always be extended later if need be.

[..]
> PS: while... waiting for such a fast/no-wait/unstable option, I see no
> reason why systemd would not work.

It does not work due to circular dependency deadlock.