[PATCH] lvm: add lvm cache logical volume handling

[Michael Chang]

The lvm cache logical volume is the logical volume consisting of the
original and the cache pool logical volume. The original is usually on a
larger and slower storage device while the cache pool is on a smaller
and faster one. The performance of the original volume can be improved
by storing the frequently used data on the cache pool to utilize the
greater performance of faster device.

The default cache mode "writethrough" ensures that any data written will
be stored both in the cache and on the origin LV, therefore grub can go
straight to read the original lv as no data loss is guarenteed.

The second cache mode is "writeback", which delays writing from the
cache pool back to the origin LV to have increased performance. The
drawback is potential data loss if losing the associated cache device.

During the boot time grub reads the LVM offline i.e. LVM volumes are not
activated and mounted, IMHO it should be fine to read directly from
original lv since all cached data should have been flushed back in the
process of taking it offline.

Signed-off-by: Michael Chang <address@hidden>
---
 grub-core/disk/lvm.c | 125 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 125 insertions(+)

diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index 32b9e289f..a1eeaa737 100644
--- a/grub-core/disk/lvm.c
+++ b/grub-core/disk/lvm.c
@@ -272,6 +272,13 @@ grub_lvm_detect (grub_disk_t disk,
 
   if (! vg)
     {
+      struct cache_lv {
+       struct grub_diskfilter_lv *lv;
+       char *cache_pool;
+       char *origin;
+       struct cache_lv *next;
+      } *cache_lvs = NULL;
+
       /* First time we see this volume group. We've to create the
         whole volume group structure. */
       vg = grub_malloc (sizeof (*vg));
@@ -701,6 +708,72 @@ grub_lvm_detect (grub_disk_t disk,
                          seg->nodes[seg->node_count - 1].name = tmp;
                        }
                    }
+                 else if (grub_memcmp (p, "cache\"",
+                                  sizeof ("cache\"") - 1) == 0)
+                   {
+                     struct cache_lv *cache;
+
+                     char *p2, *p3;
+                     grub_ssize_t sz;
+
+                     cache = grub_zalloc (sizeof (*cache));
+                     cache->lv = grub_zalloc (sizeof (*cache->lv));
+                     grub_memcpy (cache->lv, lv, sizeof (*cache->lv));
+
+                     if (lv->fullname)
+                       cache->lv->fullname = grub_strdup (lv->fullname);
+                     if (lv->idname)
+                       cache->lv->idname = grub_strdup (lv->idname);
+                     if (lv->name)
+                       cache->lv->name = grub_strdup (lv->name);
+
+                     skip_lv = 1;
+
+                     if (!(p2 = grub_strstr (p, "cache_pool = \"")))
+                       goto cache_lv_fail;
+
+                     if (!(p2 = grub_strchr (p2, '"')))
+                       goto cache_lv_fail;
+
+                     p3 = ++p2;
+                     if (!(p3 = grub_strchr (p3, '"')))
+                       goto cache_lv_fail;
+
+                     sz = p3 - p2;
+
+                     cache->cache_pool = grub_malloc (sz + 1);
+                     grub_memcpy (cache->cache_pool, p2, sz);
+                     cache->cache_pool[sz] = '\0';
+
+                     if (!(p2 = grub_strstr (p, "origin = \"")))
+                       goto cache_lv_fail;
+
+                     if (!(p2 = grub_strchr (p2, '"')))
+                       goto cache_lv_fail;
+
+                     p3 = ++p2;
+                     if (!(p3 = grub_strchr (p3, '"')))
+                       goto cache_lv_fail;
+
+                     sz = p3 - p2;
+
+                     cache->origin = grub_malloc (sz + 1);
+                     grub_memcpy (cache->origin, p2, sz);
+                     cache->origin[sz] = '\0';
+
+                     cache->next = cache_lvs;
+                     cache_lvs = cache;
+                     break;
+
+                   cache_lv_fail:
+                     grub_free (cache->origin);
+                     grub_free (cache->cache_pool);
+                     grub_free (cache->lv->fullname);
+                     grub_free (cache->lv->idname);
+                     grub_free (cache->lv->name);
+                     grub_free (cache);
+                     break;
+                   }
                  else
                    {
 #ifdef GRUB_UTIL
@@ -777,6 +850,58 @@ grub_lvm_detect (grub_disk_t disk,
              }
        
       }
+
+      {
+       struct cache_lv *cache;
+
+       for (cache = cache_lvs; cache; cache = cache->next)
+         {
+           struct grub_diskfilter_lv *lv;
+
+           for (lv = vg->lvs; lv; lv = lv->next)
+             {
+               if (grub_strcmp (lv->name, cache->origin) == 0)
+                 break;
+             }
+           if (lv)
+             {
+               cache->lv->segment_count = lv->segment_count;
+               cache->lv->segments = grub_malloc (lv->segment_count * sizeof 
(*lv->segments));
+               grub_memcpy (cache->lv->segments, lv->segments, 
lv->segment_count * sizeof (*lv->segments));
+
+               for (i = 0; i < lv->segment_count; ++i)
+                 {
+                   struct grub_diskfilter_node *nodes = lv->segments[i].nodes;
+                   grub_size_t node_count = lv->segments[i].node_count;
+                   cache->lv->segments[i].nodes = grub_malloc (node_count * 
sizeof (*nodes));
+                   grub_memcpy (cache->lv->segments[i].nodes, nodes, 
node_count * sizeof (*nodes));
+                 }
+               cache->lv->vg = vg;
+               cache->lv->next = vg->lvs;
+               vg->lvs = cache->lv;
+               cache->lv = NULL;
+             }
+         }
+
+         while ((cache = cache_lvs))
+           {
+             cache_lvs = cache_lvs->next;
+
+             if (cache->lv)
+               {
+                 for (i = 0; i < cache->lv->segment_count; ++i)
+                   grub_free (cache->lv->segments[i].nodes);
+                 grub_free (cache->lv->fullname);
+                 grub_free (cache->lv->idname);
+                 grub_free (cache->lv->name);
+               }
+             grub_free (cache->lv);
+             grub_free (cache->origin);
+             grub_free (cache->cache_pool);
+             grub_free (cache);
+           }
+      }
+
       if (grub_diskfilter_vg_register (vg))
        goto fail4;
     }
-- 
2.16.4