[PATCH] Ignore RAID0 layout if the second zone has only one device

[Pascal Hambourg <pascal@xxxxxxxxxxxxxxx>]

Le 07/04/2022 à 00:55, NeilBrown wrote:
> On Wed, 06 Apr 2022, Pascal Hambourg wrote:
> > On 05/04/2022, NeilBrown wrote:
> > > On Wed, 06 Apr 2022, Pascal Hambourg wrote:
> > > > This is a question about original/alternate layout enforcement for RAID0
> > > > arrays with members of different sizes introduced by commits
> > > > c84a1372df929033cb1a0441fb57bd3932f39ac9 ("md/raid0: avoid RAID0 data
> > > > corruption due to layout confusion.)" and
> > > > 33f2c35a54dfd75ad0e7e86918dcbe4de799a56c ("md: add feature flag
> > > > MD_FEATURE_RAID0_LAYOUT").
> > > >
> > > > The layout is irrelevant if all members have the same size so the array
> > > > has only one zone. But isn't it also irrelevant if the array has two
> > > > zones and the second zone has only one device, for example if the array
> > > > has two members of different sizes ?
> > >
> > > Yes.
> >
> > So wouldn't it make sense to allow assembly even when the layout is
> > undefined, like what is done when the array has only one zone ?
> Yes.
>
> P.S.  maybe you would like to try making the code change yourself, and
> posting the patch.

Sure. In order to check the number of devices in the second zone I had
to move the layout check after all zones are set up. Is this fine ?

diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index b21e101183f4..7623811cc11c 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -128,21 +128,6 @@ static int create_strip_zones(struct mddev *mddev, struct r0conf **private_conf)
   	pr_debug("md/raid0:%s: FINAL %d zones\n",
   		 mdname(mddev), conf->nr_strip_zones);

-	if (conf->nr_strip_zones == 1) {
-		conf->layout = RAID0_ORIG_LAYOUT;
-	} else if (mddev->layout == RAID0_ORIG_LAYOUT ||
-		   mddev->layout == RAID0_ALT_MULTIZONE_LAYOUT) {
-		conf->layout = mddev->layout;
-	} else if (default_layout == RAID0_ORIG_LAYOUT ||
-		   default_layout == RAID0_ALT_MULTIZONE_LAYOUT) {
-		conf->layout = default_layout;
-	} else {
-		pr_err("md/raid0:%s: cannot assemble multi-zone RAID0 with default_layout setting\n",
-		       mdname(mddev));
-		pr_err("md/raid0: please set raid0.default_layout to 1 or 2\n");
-		err = -ENOTSUPP;
-		goto abort;
-	}
   	/*
   	 * now since we have the hard sector sizes, we can make sure
   	 * chunk size is a multiple of that sector size
@@ -273,6 +258,22 @@ static int create_strip_zones(struct mddev *mddev, struct r0conf **private_conf)
   			 (unsigned long long)smallest->sectors);
   	}

+	if (conf->nr_strip_zones == 1 || conf->strip_zone[1].nb_dev == 1) {
+		conf->layout = RAID0_ORIG_LAYOUT;
+	} else if (mddev->layout == RAID0_ORIG_LAYOUT ||
+		   mddev->layout == RAID0_ALT_MULTIZONE_LAYOUT) {
+		conf->layout = mddev->layout;
+	} else if (default_layout == RAID0_ORIG_LAYOUT ||
+		   default_layout == RAID0_ALT_MULTIZONE_LAYOUT) {
+		conf->layout = default_layout;
+	} else {
+		pr_err("md/raid0:%s: cannot assemble multi-zone RAID0 with default_layout setting\n",
+		       mdname(mddev));
+		pr_err("md/raid0: please set raid0.default_layout to 1 or 2\n");
+		err = -ENOTSUPP;
+		goto abort;
+	}
+
   	pr_debug("md/raid0:%s: done.\n", mdname(mddev));
   	*private_conf = conf;