[dm-devel] [PATCH v4 10/20] libmultipath: indicate wwid failure in dm_addmap_create()

[Benjamin Marzinski]

On Thu, Apr 12, 2018 at 10:22:19PM +0200, Martin Wilck wrote:
> On Thu, 2018-04-12 at 22:16 +0200, Martin Wilck wrote:
> > On Thu, 2018-04-12 at 13:33 -0500, Benjamin Marzinski wrote:
> > > On Wed, Apr 04, 2018 at 06:16:17PM +0200, Martin Wilck wrote:
> > > > dm_addmap_create() is where we actually try to set up a new
> > > > multipath map. Depending on the result, mark the wwid as
> > > > failed (or not), and re-trigger an uevent if necessary.
> > > > If a path changes from multipath to non-multipath, use an "add"
> > > > event to make sure LVM2 rules pick it up. Increase log level
> > > > of this event to 3.
> > > > 
> > > 
> > > By only looking at domap, we will miss instances of multipathd
> > > failing
> > > to create maps earlier in the process. This isn't necessarily
> > > wrong.
> > > It
> > > just means that we can't rely on checking
> > > /dev/shm/multipath/failed_wwids to definitively tell us whether
> > > multipathd has tried and failed to create the device.
> > 
> > Sorry, I can't follow you. Where else except in the 
> > domap->dm_addmap_create->dm_addmap() code path do we create maps?
> > I'm feeling stupid, I really can't see it.
> 
> If you were referring to other instances of multipathd which have
> already terminated (e.g. multipathd which ran in initramfs): these
> leave the failed markers under /dev/shm when they quit. That's the
> whole point of this patch. A failed marker will only be removed if a)
> the system is rebooted, or b) another attempt to create the map
> succeeds, or c) a user removes the marker manually.
> 
> But I suppose I'm still missing your point.

Any failure in ev_add_path() before the call to domap() could cause
multipath device creation to fail, without triggering this. For instance
add_map_with_path() or setup_map() can fail for a host of reasons.

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