[PATCH v2 5/9] virstoragefile: Treat backingStore as a pointer or an array

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As explain in the former patchs, backingStore can be treat an array or
a pointer.
If we have only one backingStore we have to use it as a normal ptr
but if there is more backing store, we use it as a pointer's array.

Because it would be complicated to expend backingStore manually, and do
the convertion from a pointer to an array, I've created the
virStorageSourcePushBackingStore function to help.

This function allocate an array of pointer only if there is more than 1 bs.

Because we can not remove a child from a quorum, i didn't create the function
virStorageSourcePopBackingStore.

I've changed virStorageSourceBackingStoreClear, virStorageSourceSetBackingStore
and virStorageSourceGetBackingStore to handle the case where backingStore
is an array.

Signed-off-by: Matthias Gatto <matthias.gatto@xxxxxxxxxxxx>
---
 src/conf/storage_conf.c               |  7 ++-
 src/libvirt_private.syms              |  1 +
 src/storage/storage_backend_fs.c      |  2 +
 src/storage/storage_backend_logical.c |  2 +-
 src/util/virstoragefile.c             | 89 ++++++++++++++++++++++++++++++++---
 src/util/virstoragefile.h             |  2 +
 6 files changed, 94 insertions(+), 9 deletions(-)

diff --git a/src/conf/storage_conf.c b/src/conf/storage_conf.c
index fac85fa..41887eb 100644
--- a/src/conf/storage_conf.c
+++ b/src/conf/storage_conf.c
@@ -1343,7 +1343,12 @@ virStorageVolDefParseXML(virStoragePoolDefPtr pool,
         if (VIR_ALLOC(backingStorePtr) < 0)
             goto error;
 
-        backingStorePtr = virStorageSourceSetBackingStore(&ret->target, backingStorePtr, 0);
+        if (!virStorageSourcePushBackingStore(&ret->target))
+            goto error;
+
+        backingStorePtr = virStorageSourceSetBackingStore(&ret->target,
+                                                          backingStorePtr,
+                                                          ret->target.nBackingStores - 1);
         backingStorePtr->path = backingStore;
         backingStore = NULL;
 
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 980235b..5752907 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -2033,6 +2033,7 @@ virStorageSourceParseRBDColonString;
 virStorageSourcePoolDefFree;
 virStorageSourcePoolModeTypeFromString;
 virStorageSourcePoolModeTypeToString;
+virStorageSourcePushBackingStore;
 virStorageSourceSetBackingStore;
 virStorageTypeFromString;
 virStorageTypeToString;
diff --git a/src/storage/storage_backend_fs.c b/src/storage/storage_backend_fs.c
index a3b6688..0d8c5ad 100644
--- a/src/storage/storage_backend_fs.c
+++ b/src/storage/storage_backend_fs.c
@@ -112,6 +112,8 @@ virStorageBackendProbeTarget(virStorageSourcePtr target,
 
             if (VIR_ALLOC(backingStore) < 0)
                 goto cleanup;
+            if (virStorageSourcePushBackingStore(target) == false)
+                goto cleanup;
             virStorageSourceSetBackingStore(target, backingStore, 0);
             backingStore->type = VIR_STORAGE_TYPE_NETWORK;
             backingStore->path = meta->backingStoreRaw;
diff --git a/src/storage/storage_backend_logical.c b/src/storage/storage_backend_logical.c
index fcec31f..cd8de85 100644
--- a/src/storage/storage_backend_logical.c
+++ b/src/storage/storage_backend_logical.c
@@ -148,7 +148,7 @@ virStorageBackendLogicalMakeVol(char **const groups,
      *  lv is created with "--virtualsize").
      */
     if (groups[1] && !STREQ(groups[1], "") && (groups[1][0] != '[')) {
-        if (VIR_ALLOC(vol->target.backingStore) < 0)
+        if (virStorageSourcePushBackingStore(&vol->target) == false)
             goto cleanup;
 
         if (virAsprintf(&virStorageSourceGetBackingStore(&vol->target, 0)->path, "%s/%s",
diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
index ba38827..554aa8b 100644
--- a/src/util/virstoragefile.c
+++ b/src/util/virstoragefile.c
@@ -1798,21 +1798,88 @@ virStorageSourcePoolDefCopy(const virStorageSourcePoolDef *src)
 }
 
 
+/**
+ * virStorageSourceGetBackingStore:
+ * @src: virStorageSourcePtr containing the backing stores
+ * @pos: position of the backing store to get
+ *
+ * return the backingStore at the position of @pos
+ */
 virStorageSourcePtr
-virStorageSourceGetBackingStore(const virStorageSource *src,
-                                size_t pos ATTRIBUTE_UNUSED)
+virStorageSourceGetBackingStore(const virStorageSource *src, size_t pos)
+{
+    if (!src->backingStore || (pos > 1 && pos >= src->nBackingStores))
+        return NULL;
+    if (src->nBackingStores < 2)
+        return src->backingStore;
+    return ((virStorageSourcePtr *)src->backingStore)[pos];
+}
+
+
+/**
+ * virStorageSourcePushBackingStore:
+ * @src: virStorageSourcePtr to allocate the new backing store
+ *
+ * Allocate size for a new backingStorePtr in src->backingStore
+ * and update src->nBackingStores
+ * If we have less than 2 backing stores, we treat src->backingStore
+ * as a pointer otherwise we treat it as an array of virStorageSourcePtr
+ */
+bool
+virStorageSourcePushBackingStore(virStorageSourcePtr src)
 {
-    return src->backingStore;
+    virStorageSourcePtr     tmp;
+    virStorageSourcePtr     *tmp2;
+
+    if (!src)
+        return false;
+    if (src->nBackingStores == 1) {
+        /* If we need more than one backing store we need an array
+         * Because we don't want to lose our data from the old Backing Store
+         * we copy the pointer from src->backingStore to src->backingStore[0] */
+        tmp = src->backingStore;
+        if (VIR_ALLOC_N(tmp2, 1) < 0)
+            return false;
+        src->backingStore = (virStorageSourcePtr)tmp2;
+        src->nBackingStores += 1;
+        virStorageSourceSetBackingStore(src, tmp, 0);
+    } else if (src->nBackingStores > 1) {
+        tmp2 = ((virStorageSourcePtr *)src->backingStore);
+        if (VIR_EXPAND_N(tmp2, src->nBackingStores, 1) < 0)
+            return false;
+        src->backingStore = (virStorageSourcePtr)tmp2;
+    } else {
+        /* Most of the time we use only one backingStore
+         * So we don't need to allocate an array */
+        src->nBackingStores += 1;
+    }
+    return true;
 }
 
 
+/**
+ * virStorageSourceSetBackingStore:
+ * @src: virStorageSourcePtr to hold @backingStore
+ * @backingStore: backingStore to store
+ * @pos: position of the backing store to store
+ *
+ * Set @backingStore at @pos in src->backingStore
+ */
 virStorageSourcePtr
 virStorageSourceSetBackingStore(virStorageSourcePtr src,
                                 virStorageSourcePtr backingStore,
-                                size_t pos ATTRIBUTE_UNUSED)
+                                size_t pos)
 {
-    src->backingStore = backingStore;
-    return src->backingStore;
+    if (!src || (pos > 1 && pos >= src->nBackingStores))
+        goto error;
+    if (src->nBackingStores > 1) {
+        ((virStorageSourcePtr *)src->backingStore)[pos] = backingStore;
+    } else {
+        src->backingStore = backingStore;
+    }
+    return backingStore;
+ error:
+    return NULL;
 }
 
 
@@ -2023,6 +2090,8 @@ virStorageSourceIsEmpty(virStorageSourcePtr src)
 void
 virStorageSourceBackingStoreClear(virStorageSourcePtr def)
 {
+    size_t i;
+
     if (!def)
         return;
 
@@ -2030,7 +2099,13 @@ virStorageSourceBackingStoreClear(virStorageSourcePtr def)
     VIR_FREE(def->backingStoreRaw);
 
     /* recursively free backing chain */
-    virStorageSourceFree(virStorageSourceGetBackingStore(def, 0));
+    for (i = 0; i < def->nBackingStores; ++i)
+        virStorageSourceFree(virStorageSourceGetBackingStore(def, i));
+    if (def->nBackingStores > 1) {
+        /* in this case def->backingStores is treat as an array so we have to free it*/
+        VIR_FREE(def->backingStore);
+    }
+    def->nBackingStores = 0;
     virStorageSourceSetBackingStore(def, NULL, 0);
 }
 
diff --git a/src/util/virstoragefile.h b/src/util/virstoragefile.h
index d5cf7e6..74c363b 100644
--- a/src/util/virstoragefile.h
+++ b/src/util/virstoragefile.h
@@ -271,6 +271,7 @@ struct _virStorageSource {
 
     /* backing chain of the storage source */
     virStorageSourcePtr backingStore;
+    size_t      nBackingStores;
 
     /* metadata for storage driver access to remote and local volumes */
     virStorageDriverDataPtr drv;
@@ -294,6 +295,7 @@ virStorageSourcePtr virStorageSourceSetBackingStore(virStorageSourcePtr src,
                                                     size_t pos);
 virStorageSourcePtr virStorageSourceGetBackingStore(const virStorageSource *src,
                                                     size_t pos);
+bool virStorageSourcePushBackingStore(virStorageSourcePtr src);
 
 int virStorageFileProbeFormat(const char *path, uid_t uid, gid_t gid);
 int virStorageFileProbeFormatFromBuf(const char *path,
-- 
1.8.3.1

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