md: add feature flag MD_FEATURE_RAID0_LAYOUT

Due to a bug introduced in Linux 3.14 we cannot determine the
correctly layout for a multi-zone RAID0 array - there are two
possibilities.

It is possible to tell the kernel which to chose using a module
parameter, but this can be clumsy to use.  It would be best if
the choice were recorded in the metadata.
So add a feature flag for this purpose.
If it is set, then the 'layout' field of the superblock is used
to determine which layout to use.

If this flag is not set, then mddev->layout gets set to -1,
which causes the module parameter to be required.

Acked-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Song Liu <songliubraving@fb.com>

3 files changed, 18 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 73d5a1b04022..1be7abeb24fd 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1237,6 +1237,8 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
                         mddev->new_layout = mddev->layout;
                         mddev->new_chunk_sectors = mddev->chunk_sectors;
                 }
+                if (mddev->level == 0)
+                        mddev->layout = -1;
 
                 if (sb->state & (1<<MD_SB_CLEAN))
                         mddev->recovery_cp = MaxSector;
@@ -1652,6 +1654,10 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
                 rdev->ppl.sector = rdev->sb_start + rdev->ppl.offset;
         }
 
+        if ((le32_to_cpu(sb->feature_map) & MD_FEATURE_RAID0_LAYOUT) &&
+            sb->level != 0)
+                return -EINVAL;
+
         if (!refdev) {
                 ret = 1;
         } else {
@@ -1762,6 +1768,10 @@ static int super_1_validate(struct mddev *mddev, struct md_rdev *rdev)
                         mddev->new_chunk_sectors = mddev->chunk_sectors;
                 }
 
+                if (mddev->level == 0 &&
+                    !(le32_to_cpu(sb->feature_map) & MD_FEATURE_RAID0_LAYOUT))
+                        mddev->layout = -1;
+
                 if (le32_to_cpu(sb->feature_map) & MD_FEATURE_JOURNAL)
                         set_bit(MD_HAS_JOURNAL, &mddev->flags);
 
@@ -6898,6 +6908,9 @@ static int set_array_info(struct mddev *mddev, mdu_array_info_t *info)
         mddev->external      = 0;
 
         mddev->layout        = info->layout;
+        if (mddev->level == 0)
+                /* Cannot trust RAID0 layout info here */
+                mddev->layout = -1;
         mddev->chunk_sectors = info->chunk_size >> 9;
 
         if (mddev->persistent) {
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index ec611abda835..f61693e59684 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -145,6 +145,9 @@ static int create_strip_zones(struct mddev *mddev, struct r0conf **private_conf)
 
         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;
diff --git a/include/uapi/linux/raid/md_p.h b/include/uapi/linux/raid/md_p.h
index b0d15c73f6d7..1f2d8c81f0e0 100644
--- a/include/uapi/linux/raid/md_p.h
+++ b/include/uapi/linux/raid/md_p.h
@@ -329,6 +329,7 @@ struct mdp_superblock_1 {
 #define MD_FEATURE_JOURNAL              512 /* support write cache */
 #define MD_FEATURE_PPL                  1024 /* support PPL */
 #define MD_FEATURE_MULTIPLE_PPLS        2048 /* support for multiple PPLs */
+#define MD_FEATURE_RAID0_LAYOUT         4096 /* layout is meaningful for RAID0 */
 #define MD_FEATURE_ALL                  (MD_FEATURE_BITMAP_OFFSET       \
                                         |MD_FEATURE_RECOVERY_OFFSET     \
                                         |MD_FEATURE_RESHAPE_ACTIVE      \
@@ -341,6 +342,7 @@ struct mdp_superblock_1 {
                                         |MD_FEATURE_JOURNAL             \
                                         |MD_FEATURE_PPL                 \
                                         |MD_FEATURE_MULTIPLE_PPLS       \
+                                        |MD_FEATURE_RAID0_LAYOUT        \
                                         )
 
 struct r5l_payload_header {