Avoid shuffling remaining mirror images when removing one, retaining primary.

diff --git a/WHATS_NEW b/WHATS_NEW
index 204acb1b2960fe1b7bdeaf43ace61a37701f4122..055ce7aba14e264b5b9df379cd024a434760c760 100644 (file)
--- a/WHATS_NEW
+++ b/WHATS_NEW
@@ -1,5 +1,6 @@
 Version 2.02.40 - 
 ================================
+  Avoid shuffling remaining mirror images when removing one, retaining primary.
   Add missing LV error target activation in _remove_mirror_images.
   Prevent resizing an LV while lvconvert is using it.
   Avoid repeatedly wiping cache while VG_GLOBAL is held in vgscan & pvscan.

diff --git a/lib/metadata/metadata-exported.h b/lib/metadata/metadata-exported.h
index e42597a2e3ac78f5edebd16834be0fe58d9fa732..a53905953c0806fc375af18f319e31cfef6fa738 100644 (file)
--- a/lib/metadata/metadata-exported.h
+++ b/lib/metadata/metadata-exported.h
@@ -532,6 +532,7 @@ int add_mirror_log(struct cmd_context *cmd, struct logical_volume *lv,
 int reconfigure_mirror_images(struct lv_segment *mirrored_seg, uint32_t num_mirrors,
                              struct list *removable_pvs, unsigned remove_log);
 int collapse_mirrored_lv(struct logical_volume *lv);
+int shift_mirror_images(struct lv_segment *mirrored_seg, unsigned mimage);
 
 struct logical_volume *find_pvmove_lv(struct volume_group *vg,
                                      struct device *dev, uint32_t lv_type);

diff --git a/lib/metadata/mirror.c b/lib/metadata/mirror.c
index 5d9b355ca3767a8f0bfe9aef108fe6e21480d987..0e4afe7666cb465edfbabf71dfe8f82f2cab57f9 100644 (file)
--- a/lib/metadata/mirror.c
+++ b/lib/metadata/mirror.c
@@ -135,6 +135,53 @@ uint32_t adjusted_mirror_region_size(uint32_t extent_size, uint32_t extents,
        return region_size;
 }
 
+/*
+ * shift_mirror_images
+ * @mirrored_seg
+ * @mimage:  The position (index) of the image to move to the end
+ *
+ * When dealing with removal of legs, we often move a 'removable leg'
+ * to the back of the 'areas' array.  It is critically important not
+ * to simply swap it for the last area in the array.  This would have
+ * the affect of reordering the remaining legs - altering position of
+ * the primary.  So, we must shuffle all of the areas in the array
+ * to maintain their relative position before moving the 'removable
+ * leg' to the end.
+ *
+ * Short illustration of the problem:
+ *   - Mirror consists of legs A, B, C and we want to remove A
+ *   - We swap A and C and then remove A, leaving C, B
+ * This scenario is problematic in failure cases where A dies, because
+ * B becomes the primary.  If the above happens, we effectively throw
+ * away any changes made between the time of failure and the time of
+ * restructuring the mirror.
+ *
+ * So, any time we want to move areas to the end to be removed, use
+ * this function.
+ */
+int shift_mirror_images(struct lv_segment *mirrored_seg, unsigned mimage)
+{
+       int i;
+       struct lv_segment_area area;
+
+       if (mimage >= mirrored_seg->area_count) {
+               log_error("Invalid index (%u) of mirror image supplied "
+                         "to shift_mirror_images()", mimage);
+               return 0;
+       }
+
+       area = mirrored_seg->areas[mimage];
+
+       /* Shift remaining images down to fill the hole */
+       for (i = mimage + 1; i < mirrored_seg->area_count; i++)
+               mirrored_seg->areas[i-1] = mirrored_seg->areas[i];
+
+       /* Place this one at the end */
+       mirrored_seg->areas[i-1] = area;
+
+       return 0;
+}
+
 /*
  * This function writes a new header to the mirror log header to the lv
  *
@@ -469,13 +516,12 @@ static int _remove_mirror_images(struct logical_volume *lv,
                for (s = 0; s < mirrored_seg->area_count &&
                            old_area_count - new_area_count < num_removed; s++) {
                        sub_lv = seg_lv(mirrored_seg, s);
+
                        if (!is_temporary_mirror_layer(sub_lv) &&
                            _is_mirror_image_removable(sub_lv, removable_pvs)) {
-                               /* Swap segment to end */
+                               if (!shift_mirror_images(mirrored_seg, s))
+                                       return_0;
                                new_area_count--;
-                               area = mirrored_seg->areas[new_area_count];
-                               mirrored_seg->areas[new_area_count] = mirrored_seg->areas[s];
-                               mirrored_seg->areas[s] = area;
                        }
                }
                if (num_removed && old_area_count == new_area_count)

diff --git a/tools/vgreduce.c b/tools/vgreduce.c
index 5e6138245fc7149734ac72c74679de1994704fca..f2a5e218b820a22d088424dc12bbd47d8334fc86 100644 (file)
--- a/tools/vgreduce.c
+++ b/tools/vgreduce.c
@@ -250,9 +250,8 @@ static int _make_vg_consistent(struct cmd_context *cmd, struct volume_group *vg)
                                            lvl2->lv != seg_lv(mirrored_seg, s))
                                                continue;
                                        list_del(&lvl2->list);
-                                       area = mirrored_seg->areas[mimages - 1];
-                                       mirrored_seg->areas[mimages - 1] = mirrored_seg->areas[s];
-                                       mirrored_seg->areas[s] = area;
+                                       if (!shift_mirror_images(mirrored_seg, s))
+                                               return_0;
                                        mimages--;      /* FIXME Assumes uniqueness */
                                }
                        }