[dm-devel] [RFC PATCH] multipathd: use 0 for initial pg if nr_priority_groups=0 (was: Re: [PATCH 2/2] dm mpath: allow table load with 0 priority groups)
Mike Snitzer
snitzer at redhat.com
Mon Jan 31 18:34:46 UTC 2011
On Mon, Jan 31 2011 at 1:09pm -0500,
Moger, Babu <Babu.Moger at lsi.com> wrote:
> Looks good to me.
>
> > -----Original Message-----
> > From: Mike Snitzer [mailto:snitzer at redhat.com]
> > Sent: Monday, January 31, 2011 10:14 AM
> > To: dm-devel at redhat.com
> > Cc: Mike Snitzer; Moger, Babu
> > Subject: [PATCH 2/2] dm mpath: allow table load with 0 priority groups
> >
> > If an mpath device is held open when all paths in the last priority
> > group have failed userspace multipathd will attempt to reload the
> > associated DM table to reflect that the device no longer has any
> > priority groups. But the reload attempt always failed because the
> > multipath target did not allow 0 priority groups.
> >
> > Adjust multipath target to allow a table with both 0 priority groups
> > and 0 for the initial priority group number.
> >
> > All multipath target messages related to priority group (enable_group,
> > disable_group, switch_group) will properly handle a priority group of
> > 0 (will cause error).
> >
> > When reloading a multipath table with 0 priority groups, userspace
> > multipathd must be updated to specify an initial priority group number
> > of 0 (rather than 1).
>
> Looks like we still have some action from multipath tool. CCing Ben..
Right, I looked in to the multipath-tools change. Here is an RFC patch.
Inlined "FIXME"s pose the relevant questions. I held off on having
select_path_group() return 0 when !mpp->pg because I wasn't confident
that I wouldn't break multipathd in some unintuitive way.
I did audit the various callers (indirect through setup_map call):
update_path_groups
ev_add_path
ev_remove_path
(all above first call setup_map)
setup_map()
- mpp->bestpg = select_path_group()
- assemble_map() -- establishes mp->params
do_map()
Even though I verified that much I wasn't completely confident in
changing select_path_group()'s defualt return of 1 -- so I localized the
change to where I _knew_ it was safe (assemble_map):
diff --git a/libmultipath/dmparser.c b/libmultipath/dmparser.c
index 1ef3aad..97b6420 100644
--- a/libmultipath/dmparser.c
+++ b/libmultipath/dmparser.c
@@ -52,6 +52,7 @@ assemble_map (struct multipath * mp)
int i, j;
int shift, freechar;
int minio;
+ int nr_priority_groups, initial_pg_nr;
char * p;
struct pathgroup * pgp;
struct path * pp;
@@ -60,9 +61,19 @@ assemble_map (struct multipath * mp)
p = mp->params;
freechar = sizeof(mp->params);
+ nr_priority_groups = VECTOR_SIZE(mp->pg);
+ /*
+ * FIXME: make this conditional on multipath target version?
+ * - but no existing code is conditional on multipath target version,
+ * nor does dm_drvprereq() store the version for code to do so.
+ * - thing is older multipath never allowed nr_priority_groups=0 so
+ * it doesn't _really_ matter if initial_pg_nr=0 here...
+ */
+ initial_pg_nr = (nr_priority_groups ? mp->bestpg : 0);
+
shift = snprintf(p, freechar, "%s %s %i %i",
mp->features, mp->hwhandler,
- VECTOR_SIZE(mp->pg), mp->bestpg);
+ nr_priority_groups, initial_pg_nr);
if (shift >= freechar) {
fprintf(stderr, "mp->params too small\n");
diff --git a/libmultipath/switchgroup.c b/libmultipath/switchgroup.c
index 025a95d..82c30ad 100644
--- a/libmultipath/switchgroup.c
+++ b/libmultipath/switchgroup.c
@@ -41,7 +41,7 @@ select_path_group (struct multipath * mpp)
struct pathgroup * pgp;
if (!mpp->pg)
- return 1;
+ return 1; /* FIXME: return 0 here? */
vector_foreach_slot (mpp->pg, pgp, i) {
if (!pgp->paths)
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