[Libguestfs] [PATCH nbdkit BROKEN 2/2] vddk: Only do QueryAllocatedBlocks test once

[Richard W.M. Jones]

---
 plugins/vddk/worker.c | 67 ++++++++++++++++++++++++-------------------
 1 file changed, 38 insertions(+), 29 deletions(-)

diff --git a/plugins/vddk/worker.c b/plugins/vddk/worker.c
index 4bb7d8d7..a8ffc23e 100644
--- a/plugins/vddk/worker.c
+++ b/plugins/vddk/worker.c
@@ -305,9 +305,12 @@ do_flush (struct command *cmd)
   return 0;
 }
 
+static pthread_mutex_t extents_test_lock = PTHREAD_MUTEX_INITIALIZER;
+
 static int
 do_can_extents (struct command *cmd)
 {
+  static int extents_test = -1;
   VixError err;
   VixDiskLibBlockList *block_list;
 
@@ -320,41 +323,47 @@ do_can_extents (struct command *cmd)
     return 0;
   }
 
-  /* Suppress errors around this call.  See:
-   * https://bugzilla.redhat.com/show_bug.cgi?id=1709211#c7
-   */
-  error_suppression = 1;
-
   /* However even when the call is available it rarely works well so
    * the best thing we can do here is to try the call and if it's
    * non-functional return false.
    */
-  VDDK_CALL_START (VixDiskLib_QueryAllocatedBlocks,
-                   "handle, 0, %d sectors, %d sectors",
-                   VIXDISKLIB_MIN_CHUNK_SIZE, VIXDISKLIB_MIN_CHUNK_SIZE)
-    err = VixDiskLib_QueryAllocatedBlocks (handle,
-                                           0, VIXDISKLIB_MIN_CHUNK_SIZE,
-                                           VIXDISKLIB_MIN_CHUNK_SIZE,
-                                           &block_list);
-  VDDK_CALL_END (VixDiskLib_QueryAllocatedBlocks, 0);
-  error_suppression = 0;
-  if (err == VIX_OK) {
-    VDDK_CALL_START (VixDiskLib_FreeBlockList, "block_list")
-      VixDiskLib_FreeBlockList (block_list);
-    VDDK_CALL_END (VixDiskLib_FreeBlockList, 0);
-  }
-  if (err != VIX_OK) {
-    char *errmsg = VixDiskLib_GetErrorText (err, NULL);
-    nbdkit_debug ("can_extents: "
-                  "VixDiskLib_QueryAllocatedBlocks test failed, "
-                  "extents support will be disabled: "
-                  "original error: %s",
-                  errmsg);
-    VixDiskLib_FreeErrorText (errmsg);
-    return 0;
+  ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&extents_test_lock);
+  if (extents_test == -1) {
+    /* Suppress errors around this call.  See:
+     * https://bugzilla.redhat.com/show_bug.cgi?id=1709211#c7
+     */
+    error_suppression = 1;
+
+    VDDK_CALL_START (VixDiskLib_QueryAllocatedBlocks,
+                     "handle, 0, %d sectors, %d sectors",
+                     VIXDISKLIB_MIN_CHUNK_SIZE, VIXDISKLIB_MIN_CHUNK_SIZE)
+      err = VixDiskLib_QueryAllocatedBlocks (handle,
+                                             0, VIXDISKLIB_MIN_CHUNK_SIZE,
+                                             VIXDISKLIB_MIN_CHUNK_SIZE,
+                                             &block_list);
+    VDDK_CALL_END (VixDiskLib_QueryAllocatedBlocks, 0);
+    error_suppression = 0;
+    if (err == VIX_OK) {
+      VDDK_CALL_START (VixDiskLib_FreeBlockList, "block_list")
+        VixDiskLib_FreeBlockList (block_list);
+      VDDK_CALL_END (VixDiskLib_FreeBlockList, 0);
+
+      extents_test = 1;         /* result = good */
+    }
+    else {
+      char *errmsg = VixDiskLib_GetErrorText (err, NULL);
+      nbdkit_debug ("can_extents: "
+                    "VixDiskLib_QueryAllocatedBlocks test failed, "
+                    "extents support will be disabled: "
+                    "original error: %s",
+                    errmsg);
+      VixDiskLib_FreeErrorText (errmsg);
+
+      extents_test = 0;         /* result = bad */
+    }
   }
 
-  return 1;
+  return extents_test;
 }
 
 /* Add an extent to the list of extents. */
-- 
2.32.0