Re: [PATCH RESEND 0/4] multipath-tools: fixes for path wwid detection and path change uevents

["Benjamin Marzinski" <bmarzins@redhat.com>]

On Tue, Oct 02, 2018 at 11:02:50PM +0200, Martin Wilck wrote:
> Hi Ben, Christophe,
> 
> I found a problem with this old patch series of mine.
> 
> while I am still pondering about your latest series, it occured to me
> that my patch "get_uid: don't quit prematurely without udev" is against
> the spirit of your "retrigger uevents to try and get the uid through
> udev" patch from 2016 (688aa22b).
> 
> "get_uid: don't quit prematurely without udev" has been merged a while
> ago (08d42ee6). Should it be reverted??
> 
> Pro: the patch is against the "udev first" philosophy and subverts the
> retrigger logic.
> Con: with the patch, we'll be able to retrieve WWIDs more quickly in
> some situations, as we don't have to wait for udev.
> 
> Either way (but more likely with my patch), it may happen that we
> retrieve a WWID from sysfs or elsewhere first, and from udev later.
> These WWIDs may not necessarily match, and a "WWID changed" problem may
> occur.
> 
> Please tell me what you think.

I'm having a hard time seeing how get_uid() could get called on a path
without a udev device attached in multipathd. It can happen because of
update_paths() in multipath, for paths that don't get discovered when
searching for paths, but do belong to an existing multipath device. I
don't think you patch will hurt anything here. So, unless I'm missing
some code path in multipathd, I don't see a problem with this patch.

In fact, we should probably make scsi_uid_fallback() skip (or at least
always pass) the retrigger check if we aren't in the daemon, so we
always try the failback when we run multipath.

-Ben

> 
> Martin
> 
> 
> -- 
> Dr. Martin Wilck <mwilck@suse.com>, Tel. +49 (0)911 74053 2107
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
> HRB 21284 (AG Nürnberg)
>