Grow: fix --layout=preserve to match man page.

I think there was some confusion about what --layout=preserve
actually means, but in any case it wasn't doing what the man
page says it should.
So add some case analysis and make sure it does the right thing,
or complains if it cannot.

Reported-by: Patrik Horník <patrik@dsl.sk>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/Grow.c b/Grow.c
index 330e7195fb0444f415e6ed20c2c2eda35e6bb8a1..9350a07976552e2bb6d23f45e72dc2a1468980c7 100644 (file)
--- a/Grow.c
+++ b/Grow.c
@@ -1885,9 +1885,37 @@ size_change_error:
                                *h = 0;
                                info.new_layout = map_name(r6layout, l);
                        }
+               } else {
+                       fprintf(stderr, Name
+                               ": %s is only meaningful when reshaping"
+                               " a RAID6 array.\n", layout_str);
+                       rv = 1;
+                       goto release;
                }
        } else if (strcmp(layout_str, "preserve") == 0) {
-               info.new_layout = UnSet;
+               /* This means that a non-standard RAID6 layout
+                * is OK.
+                * In particular:
+                * - When reshape a RAID6 (e.g. adding a device)
+                *   which is in a non-standard layout, it is OK
+                *   to preserve that layout.
+                * - When converting a RAID5 to RAID6, leave it in
+                *   the XXX-6 layout, don't re-layout.
+                */
+               if (info.array.level == 6 && info.new_level == UnSet)
+                       info.new_layout = info.array.layout;
+               else if (info.array.level == 5 && info.new_level == 6) {
+                       char l[40];
+                       strcpy(l, map_num(r5layout, info.array.layout));
+                       strcat(l, "-6");
+                       info.new_layout = map_name(r6layout, l);
+               } else {
+                       fprintf(stderr, Name
+                               ": %s in only meaningful when reshaping"
+                               " to RAID6\n", layout_str);
+                       rv = 1;
+                       goto release;
+               }
        } else {
                int l = info.new_level;
                if (l == UnSet)