Re: discuss about commit 3b0f9ce: filter-mpath: get wwids from sysfs vpd_pg83

On Tue, Nov 14, 2023 at 10:44:02AM +0000, Martin Wilck wrote:
> I haven't looked into "system.devices" so far. Is there a high-level
> description of this feature available somewhere? A link would be
> appreciated. On (open)SUSE, afaik, system.device is not used (Heming,
> correct me if I am wrong).

https://man7.org/linux/man-pages/man8/lvmdevices.8.html

If that's too low-level let me know and I'll look at writing something
more conceptual and introductory.

> > - To make filter-mpath use udev info, and prevent lvm from using
> > wwids, you can set external_device_info_source=udev and
> > multipath_wwids_file="".
> 
> Good to know, but that's kind of counter-intuitive. I'd prefer
> if external_device_info_source=udev did what the name says, and a new
> mode ("external_device_info_source=hybrid", say) was introduced for the
> current behavior.

I'd also thought about adding a new option for external_device_info_source
that would mean "udev info only", rather than "both native and udev info."

The complication is that external_device_info_source applies to a few
different kinds of device info, not just multipath, and I doubt we can
apply only udev info to all those cases.  This means adding another config
option... not much different from just using multipath_wwids_file="".

> Can a distribution set multipath_wwids_file="" by default without
> undesired side effects?

Yes, it just causes lvm to skip the use of /etc/multipath/wwids for
checking if a device is a multipath component.

Dave