Re: [PATCH v4 19/20] libmultipath: enable find_multipaths "smart"

[Martin Wilck <mwilck@suse.com>]

On Thu, 2018-04-12 at 13:47 -0500, Benjamin Marzinski wrote:
> On Wed, Apr 04, 2018 at 06:16:26PM +0200, Martin Wilck wrote:
> > This activates "smart" path detection. This is similar to
> > "find_multipaths yes", but doesn't generally ignore single paths
> > that are not listed in the WWIDs file. Rather, such paths are
> > temporarily treated like multipath members. If no additional paths
> > are detected after a certain time, the paths are re-added to the
> > system as non-multipath. This needs support by the udev rules, to
> > be added in a follow-up patch.
> > 
> > If a multipath map is successfully successfully created, and paths
> > are
> > in waiting state, trigger path uevents to update their status.
> > 
> > Signed-off-by: Martin Wilck <mwilck@suse.com>
> > ---
> >  libmultipath/configure.c   | 15 ++++++++++++---
> >  libmultipath/dict.c        |  1 +
> >  multipath/multipath.conf.5 | 13 +++++++++++++
> >  3 files changed, 26 insertions(+), 3 deletions(-)
> > 
> > diff --git a/libmultipath/configure.c b/libmultipath/configure.c
> > index 9aa3d21..17c2fa1 100644
> > --- a/libmultipath/configure.c
> > +++ b/libmultipath/configure.c
> > @@ -12,6 +12,7 @@
> >  #include <string.h>
> >  #include <sys/file.h>
> >  #include <errno.h>
> > +#include <ctype.h>
> >  #include <libdevmapper.h>
> >  #include <libudev.h>
> >  #include "mpath_cmd.h"
> > @@ -476,9 +477,17 @@ trigger_paths_udev_change(struct multipath
> > *mpp, bool is_mpath)
> >  			env = udev_device_get_property_value(
> >  				pp->udev,
> > "DM_MULTIPATH_DEVICE_PATH");
> >  
> > -			if (is_mpath && env != NULL &&
> > !strcmp(env, "1"))
> > -				continue;
> > -			else if (!is_mpath &&
> 
> If DM_MULTIPATH_DEVICE_PATH=1 then there has already been a uevent
> where
> udev recognized that the device should be claimed.  Wouldn't udev
> have
> stopped the timer then?  I don't see why this is necessary.

I set DM_MULTIPATH_DEVICE_PATH=1 in the "pretend_mpath" section
in multipath.rules in the "maybe" case. The value
DM_MULTIPATH_DEVICE_PATH=2 is never passed on to other udev rules,
and never seen by multipathd.

The reason I did that was that rules may have checks like
'DM_MULTIPATH_DEVICE_PATH!="1", ...' and I wanted to avoid these to be
run in the "maybe" case, which, for all actors above multipath, 
should be temporarily treated like "yes".

I hope this explains it.

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)

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