[PATCH 1/2] Storage: Introduce shadow vol for refresh while the main vol builds.

[Prerna Saxena <prerna@xxxxxxxxxxxxxxxxxx>]

From: Prerna Saxena <prerna@xxxxxxxxxxxxxxxxxx>
Date: Thu, 18 Jun 2015 05:05:09 -0500

Libvirt periodically refreshes all volumes in a storage pool, including
the volumes being cloned.
While cloning a storage volume from parent, we drop pool locks. Subsequent
volume refresh sometimes changes allocation for an ongoing copy, and leads
to corrupt images.
Fix: Introduce a shadow volume that isolates the volume object under refresh
from the base which has a copy ongoing.

Signed-off-by: Prerna Saxena <prerna@xxxxxxxxxxxxxxxxxx>
---
 src/storage/storage_driver.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
index 57060ab..4980546 100644
--- a/src/storage/storage_driver.c
+++ b/src/storage/storage_driver.c
@@ -1898,7 +1898,7 @@ storageVolCreateXMLFrom(virStoragePoolPtr obj,
 {
     virStoragePoolObjPtr pool, origpool = NULL;
     virStorageBackendPtr backend;
-    virStorageVolDefPtr origvol = NULL, newvol = NULL;
+    virStorageVolDefPtr origvol = NULL, newvol = NULL, shadowvol = NULL;
     virStorageVolPtr ret = NULL, volobj = NULL;
     unsigned long long allocation;
     int buildret;
@@ -2010,6 +2010,17 @@ storageVolCreateXMLFrom(virStoragePoolPtr obj,
     if (backend->createVol(obj->conn, pool, newvol) < 0)
         goto cleanup;
 
+    /* Make a shallow copy of the 'defined' volume definition, since the
+     * original allocation value will change as the user polls 'info',
+     * but we only need the initial requested values
+     */
+    if (VIR_ALLOC(shadowvol) < 0) {
+        newvol = NULL;
+        goto cleanup;
+    }
+
+    memcpy(shadowvol, newvol, sizeof(*newvol));
+
     pool->volumes.objs[pool->volumes.count++] = newvol;
     volobj = virGetStorageVol(obj->conn, pool->def->name, newvol->name,
                               newvol->key, NULL, NULL);
@@ -2029,7 +2040,7 @@ storageVolCreateXMLFrom(virStoragePoolPtr obj,
         virStoragePoolObjUnlock(origpool);
     }
 
-    buildret = backend->buildVolFrom(obj->conn, pool, newvol, origvol, flags);
+    buildret = backend->buildVolFrom(obj->conn, pool, shadowvol, origvol, flags);
 
     storageDriverLock();
     virStoragePoolObjLock(pool);
-- 
1.8.3.1

-- 
Prerna Saxena

Linux Technology Centre,
IBM Systems and Technology Lab,
Bangalore, India

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