dm mpath: use more error codes

This patch allows path errors from the multipath ctr function to
propagate up to userspace as errno values from the ioctl() call.

This is in response to
  https://www.redhat.com/archives/dm-devel/2008-May/msg00000.html
and
  https://bugzilla.redhat.com/show_bug.cgi?id=444421

The patch only lets through the errors that it needs to in order to
get the path errors from parse_path().
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-mpath.c

@@ -563,12 +563,12 @@ static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
 	/* we need at least a path arg */
 	if (as->argc < 1) {
 		ti->error = "no device given";
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	}
 
 	p = alloc_pgpath();
 	if (!p)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 
 	r = dm_get_device(ti, shift(as), ti->begin, ti->len,
 			  dm_table_get_mode(ti->table), &p->path.dev);
@@ -596,7 +596,7 @@ static struct pgpath *parse_path(struct arg_set *as, struct path_selector *ps,
 
  bad:
 	free_pgpath(p);
-	return NULL;
+	return ERR_PTR(r);
 }
 
 static struct priority_group *parse_priority_group(struct arg_set *as,
@@ -614,14 +614,14 @@ static struct priority_group *parse_priority_group(struct arg_set *as,
 
 	if (as->argc < 2) {
 		as->argc = 0;
-		ti->error = "not enough priority group aruments";
-		return NULL;
+		ti->error = "not enough priority group arguments";
+		return ERR_PTR(-EINVAL);
 	}
 
 	pg = alloc_priority_group();
 	if (!pg) {
 		ti->error = "couldn't allocate priority group";
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	}
 	pg->m = m;
 
@@ -654,8 +654,10 @@ static struct priority_group *parse_priority_group(struct arg_set *as,
 		path_args.argv = as->argv;
 
 		pgpath = parse_path(&path_args, &pg->ps, ti);
-		if (!pgpath)
+		if (IS_ERR(pgpath)) {
+			r = PTR_ERR(pgpath);
 			goto bad;
+		}
 
 		pgpath->pg = pg;
 		list_add_tail(&pgpath->list, &pg->pgpaths);
@@ -666,7 +668,7 @@ static struct priority_group *parse_priority_group(struct arg_set *as,
 
  bad:
 	free_priority_group(pg, ti);
-	return NULL;
+	return ERR_PTR(r);
 }
 
 static int parse_hw_handler(struct arg_set *as, struct multipath *m)
@@ -785,8 +787,8 @@ static int multipath_ctr(struct dm_target *ti, unsigned int argc,
 		struct priority_group *pg;
 
 		pg = parse_priority_group(&as, m);
-		if (!pg) {
-			r = -EINVAL;
+		if (IS_ERR(pg)) {
+			r = PTR_ERR(pg);
 			goto bad;
 		}