[RFC PATCH 3/3] libvirt: Implement two-tier driver loading

[Adam Walters <adam@xxxxxxxxxxxxxxxxx>]

This implements a two-tier driver loading system into libvirt. The two classes of drivers are "Libvirt" drivers and "Hypervisor" drivers. Hypervisor drivers are fairly self-explanatory, they provide domain services. Libvirt drivers are sort of the backend drivers for those, like the secret and storage drivers. In the two-tier loading system here, the "Libvirt" drivers are all loaded and auto-started. Once those have finished, the "Hypervisor" drivers are loaded and auto-started. By doing things in this manner, we do not have to hard-code a driver loading order or roll our own dynamic dependency-based loading algorithm, while still gaining the benefits of a more orderly driver loading approach, which should help minimize the possibility of a race condition during startup. If another race condition is found, the code can be extended to provide any number of extra tiers without much trouble.

Signed-off-by: Adam Walters <adam@xxxxxxxxxxxxxxxxx>
---
 src/libvirt.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 49 insertions(+), 8 deletions(-)

diff --git a/src/libvirt.c b/src/libvirt.c
index 77f481e..9c00491 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -837,31 +837,72 @@ int virStateInitialize(bool privileged,
                        void *opaque)
 {
     size_t i;
+    virStateDriverPtr virLibvirtStateDriverTab[MAX_DRIVERS];
+    int virLibvirtStateDriverTabCount = 0;
+    virStateDriverPtr virHypervisorStateDriverTab[MAX_DRIVERS];
+    int virHypervisorStateDriverTabCount = 0;
 
     if (virInitialize() < 0)
         return -1;
 
     for (i = 0; i < virStateDriverTabCount; i++) {
-        if (virStateDriverTab[i]->stateInitialize) {
+        switch (virStateDriverTab[i]->stateType) {
+        case VIR_DRV_STATE_DRV_LIBVIRT:
+            virLibvirtStateDriverTab[virLibvirtStateDriverTabCount++] =
+                virStateDriverTab[i];
+            break;
+        case VIR_DRV_STATE_DRV_HYPERVISOR:
+            virHypervisorStateDriverTab[virHypervisorStateDriverTabCount++] =
+                virStateDriverTab[i];
+            break;
+        }
+    }
+
+    for (i = 0; i < virLibvirtStateDriverTabCount; i++) {
+        if (virLibvirtStateDriverTab[i]->stateInitialize) {
             VIR_DEBUG("Running global init for %s state driver",
-                      virStateDriverTab[i]->name);
-            if (virStateDriverTab[i]->stateInitialize(privileged,
+                      virLibvirtStateDriverTab[i]->name);
+            if (virLibvirtStateDriverTab[i]->stateInitialize(privileged,
                                                       callback,
                                                       opaque) < 0) {
                 virErrorPtr err = virGetLastError();
                 VIR_ERROR(_("Initialization of %s state driver failed: %s"),
-                          virStateDriverTab[i]->name,
+                          virLibvirtStateDriverTab[i]->name,
                           err && err->message ? err->message : _("Unknown problem"));
                 return -1;
             }
         }
     }
 
-    for (i = 0; i < virStateDriverTabCount; i++) {
-        if (virStateDriverTab[i]->stateAutoStart) {
+    for (i = 0; i < virLibvirtStateDriverTabCount; i++) {
+        if (virLibvirtStateDriverTab[i]->stateAutoStart) {
+            VIR_DEBUG("Running global auto start for %s state driver",
+                      virLibvirtStateDriverTab[i]->name);
+            virLibvirtStateDriverTab[i]->stateAutoStart();
+        }
+    }
+
+    for (i = 0; i < virHypervisorStateDriverTabCount; i++) {
+        if (virHypervisorStateDriverTab[i]->stateInitialize) {
+            VIR_DEBUG("Running global init for %s state driver",
+                      virHypervisorStateDriverTab[i]->name);
+            if (virHypervisorStateDriverTab[i]->stateInitialize(privileged,
+                                                      callback,
+                                                      opaque) < 0) {
+                virErrorPtr err = virGetLastError();
+                VIR_ERROR(_("Initialization of %s state driver failed: %s"),
+                          virHypervisorStateDriverTab[i]->name,
+                          err && err->message ? err->message : _("Unknown problem"));
+                return -1;
+            }
+        }
+    }
+
+    for (i = 0; i < virHypervisorStateDriverTabCount; i++) {
+        if (virHypervisorStateDriverTab[i]->stateAutoStart) {
             VIR_DEBUG("Running global auto start for %s state driver",
-                      virStateDriverTab[i]->name);
-            virStateDriverTab[i]->stateAutoStart();
+                      virHypervisorStateDriverTab[i]->name);
+            virHypervisorStateDriverTab[i]->stateAutoStart();
         }
     }
     return 0;
-- 
1.8.5.2

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