[libvirt] [PATCHv2 11/16] storage: make it easier to find file within chain

[Eric Blake]

In order to temporarily label files read/write during a commit
operation, we need to crawl the backing chain and find the absolute
file name that needs labeling in the first place, as well as the
name of the file that owns the backing file.

* src/util/storage_file.c (virStorageFileChainLookup): New
function.
* src/util/storage_file.h: Declare it.
* src/libvirt_private.syms (storage_file.h): Export it.
---
 src/libvirt_private.syms |  1 +
 src/util/storage_file.c  | 63 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/util/storage_file.h  |  7 ++++++
 3 files changed, 71 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index fe31bbe..e40d630 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1125,6 +1125,7 @@ virStorageGenerateQcowPassphrase;


 # storage_file.h
+virStorageFileChainLookup;
 virStorageFileFormatTypeFromString;
 virStorageFileFormatTypeToString;
 virStorageFileFreeMetadata;
diff --git a/src/util/storage_file.c b/src/util/storage_file.c
index 6f299c0..218891e 100644
--- a/src/util/storage_file.c
+++ b/src/util/storage_file.c
@@ -1260,3 +1260,66 @@ const char *virStorageFileGetSCSIKey(const char *path)
     return NULL;
 }
 #endif
+
+/* Given a CHAIN that starts at the named file START, return the
+ * canonical name for the backing file NAME within that chain, or pass
+ * NULL to find the base of the chain.  If *META is not NULL, set it
+ * to the point in the chain that describes NAME (or to NULL if the
+ * backing element is not a file).  If *PARENT is not NULL, set it to
+ * the canonical name of the parent (or to NULL if NAME matches
+ * START).  The results point within CHAIN, and must not be
+ * independently freed.  */
+const char *
+virStorageFileChainLookup(virStorageFileMetadataPtr chain, const char *start,
+                          const char *name, virStorageFileMetadataPtr *meta,
+                          const char **parent)
+{
+    virStorageFileMetadataPtr owner;
+    const char *tmp;
+
+    if (!parent)
+        parent = &tmp;
+
+    *parent = NULL;
+    if (name ? STREQ(start, name) || virFileLinkPointsTo(start, name) :
+        !chain->backingStore) {
+        if (meta)
+            *meta = chain;
+        return start;
+    }
+
+    owner = chain;
+    *parent = start;
+    while (owner) {
+        if (!owner->backingStore)
+            goto error;
+        if (!name) {
+            if (!owner->backingMeta ||
+                !owner->backingMeta->backingStore)
+                break;
+        } else if (STREQ_NULLABLE(name, owner->backingStoreRaw) ||
+                   STREQ(name, owner->backingStore)) {
+            break;
+        } else if (owner->backingStoreIsFile) {
+            char *abs = absolutePathFromBaseFile(*parent, name);
+            if (abs && STREQ(abs, owner->backingStore)) {
+                VIR_FREE(abs);
+                break;
+            }
+            VIR_FREE(abs);
+        }
+        *parent = owner->backingStore;
+        owner = owner->backingMeta;
+    }
+    if (!owner)
+        goto error;
+    if (meta)
+        *meta = owner->backingMeta;
+    return owner->backingStore;
+
+error:
+    *parent = NULL;
+    if (meta)
+        *meta = NULL;
+    return NULL;
+}
diff --git a/src/util/storage_file.h b/src/util/storage_file.h
index 685fcb8..9b00dba 100644
--- a/src/util/storage_file.h
+++ b/src/util/storage_file.h
@@ -78,6 +78,13 @@ virStorageFileMetadataPtr virStorageFileGetMetadataFromFD(const char *path,
                                                           int fd,
                                                           int format);

+const char *virStorageFileChainLookup(virStorageFileMetadataPtr chain,
+                                      const char *start,
+                                      const char *name,
+                                      virStorageFileMetadataPtr *meta,
+                                      const char **parent)
+    ATTRIBUTE_NONNULL(1) ATTRIBUTE_NONNULL(2);
+
 void virStorageFileFreeMetadata(virStorageFileMetadataPtr meta);

 int virStorageFileResize(const char *path, unsigned long long capacity);
-- 
1.7.11.7