[dm-devel] [PATCH 5/5] libmultipath: fix ALUA autodetection when paths are down

[Martin Wilck]

On Tue, 2019-11-19 at 16:29 -0600, Benjamin Marzinski wrote:
> On Fri, Nov 15, 2019 at 02:41:54PM +0000, Martin Wilck wrote:
> > From: Martin Wilck <mwilck at suse.com>
> > 
> > If a single path was offline when detect_alua() was called,
> > multipathd would assume ALUA was generally unsupported.
> > 
> > Fix that by assuming that if at least one path has ALUA support and
> > no path explicitly does not have it, ALUA is supported.
> > 
> > Signed-off-by: Martin Wilck <mwilck at suse.com>
> > ---
> >  libmultipath/discovery.c | 22 +++++++++++++++++++++-
> >  libmultipath/propsel.c   | 20 +++++++++++++++++---
> >  2 files changed, 38 insertions(+), 4 deletions(-)
> > 
> > diff --git a/libmultipath/discovery.c b/libmultipath/discovery.c
> > index 4288c9fd..5f41dcb7 100644
> > --- a/libmultipath/discovery.c
> > +++ b/libmultipath/discovery.c
> > @@ -871,6 +871,10 @@ get_serial (char * str, int maxlen, int fd)
> >  	return 1;
> >  }
> >  
> > /*
> > + * Side effect: sets pp->tpgs if it could be determined.
> > + * If ALUA calls fail because paths are unreachable, pp->tpgs
> > remains unchanged.
> > + */
> >  static void
> >  detect_alua(struct path * pp)
> >  {
> > @@ -881,12 +885,28 @@ detect_alua(struct path * pp)
> >  	if (sysfs_get_timeout(pp, &timeout) <= 0)
> >  		timeout = DEF_TIMEOUT;
> >  
> > -	if ((tpgs = get_target_port_group_support(pp, timeout)) <= 0) {
> > +	tpgs = get_target_port_group_support(pp, timeout);
> > +	if (tpgs == -RTPG_INQUIRY_FAILED)
> > +		return;
> > +	else if (tpgs <= 0) {
> >  		pp->tpgs = TPGS_NONE;
> >  		return;
> >  	}
> > +
> > +	if (pp->fd == -1 || pp->offline)
> > +		return;
> > +
>  
> This is just a nitpick, but won't tpgs already be
> -RTPG_INQUIRY_FAILED
> if pp->fd == -1. This check makes more sense before
> get_target_port_group_support().

Not really, because get_target_port_group_support() normally obtains
INQUIRY data from sysfs, which can return something reasonable even
if fd == -1 (e.g. if the path is temporarily offline). In particular,
it could indicate that the device has no TPGS support. That's why I
call it first.

Regards,
Martin