cache: support activation of empty cache-pool

When the cache pool is unused, lvm2 code will internally
allow to activate such cache-pool.

Cache-pool is activate as metadata LV, so lvm2 could easily
wipe such volume before cache-pool is reused.

diff --git a/lib/activate/dev_manager.c b/lib/activate/dev_manager.c
index e9b68161fa4cf9755ee5f88b03f7bcd124c3f232..9272742bc2212566d5c6060b4b7dae7503b7f1cf 100644 (file)
--- a/lib/activate/dev_manager.c
+++ b/lib/activate/dev_manager.c
@@ -1867,12 +1867,15 @@ static int _add_lv_to_dtree(struct dev_manager *dm, struct dm_tree *dtree,
        const char *uuid;
 
        if (lv_is_cache_pool(lv)) {
-               /* origin_only is ignored */
-               /* cache pool is 'meta' LV and does not have a real device node */
-               if (!_add_lv_to_dtree(dm, dtree, seg_lv(first_seg(lv), 0), 0))
-                       return_0;
-               if (!_add_lv_to_dtree(dm, dtree, first_seg(lv)->metadata_lv, 0))
-                       return_0;
+               if (!dm_list_empty(&lv->segs_using_this_lv)) {
+                       /* origin_only is ignored */
+                       /* cache pool is 'meta' LV and does not have a real device node */
+                       if (!_add_lv_to_dtree(dm, dtree, seg_lv(first_seg(lv), 0), 0))
+                               return_0;
+                       if (!_add_lv_to_dtree(dm, dtree, first_seg(lv)->metadata_lv, 0))
+                               return_0;
+               } else if (!_add_dev_to_dtree(dm, dtree, lv, NULL))
+                       return_0; /* For internal use - empty pool makes meta visible */
                return 1;
        }
 
@@ -2560,7 +2563,8 @@ static int _add_new_lv_to_dtree(struct dev_manager *dm, struct dm_tree *dtree,
        uint32_t read_ahead = lv->read_ahead;
        uint32_t read_ahead_flags = UINT32_C(0);
 
-       if (lv_is_cache_pool(lv)) {
+       if (lv_is_cache_pool(lv) &&
+           !dm_list_empty(&lv->segs_using_this_lv)) {
                /* cache pool is 'meta' LV and does not have a real device node */
                if (!_add_new_lv_to_dtree(dm, dtree, seg_lv(first_seg(lv), 0), laopts, NULL))
                        return_0;
@@ -2637,6 +2641,10 @@ static int _add_new_lv_to_dtree(struct dev_manager *dm, struct dm_tree *dtree,
        /* Create table */
        dm->pvmove_mirror_count = 0u;
 
+       /* This is unused cache-pool - make metadata accessible */
+       if (lv_is_cache_pool(lv))
+               lv = first_seg(lv)->metadata_lv;
+
        /* If this is a snapshot origin, add real LV */
        /* If this is a snapshot origin + merging snapshot, add cow + real LV */
        /* Snapshot origin could be also external origin */
@@ -2853,7 +2861,7 @@ static int _tree_action(struct dev_manager *dm, const struct logical_volume *lv,
 
        /* Some LV can be used for top level tree */
        /* TODO: add more.... */
-       if (lv_is_cache_pool(lv)) {
+       if (lv_is_cache_pool(lv) && !dm_list_empty(&lv->segs_using_this_lv)) {
                log_error(INTERNAL_ERROR "Cannot create tree for %s.", lv->name);
                return 0;
        }