[libvirt] [PATCH 04/12] storage: acquire a pidfile in the driver root directory

[Daniel P. Berrangé]

When we allow multiple instances of the driver for the same user
account, using a separate root directory, we need to ensure mutual
exclusion. Use a pidfile to guarantee this.

In privileged libvirtd this ends up locking

   /var/run/libvirt/storage/driver.pid

In unprivileged libvirtd this ends up locking

  /run/user/$UID/libvirt/storage/run/driver.pid

NB, the latter can vary depending on $XDG_RUNTIME_DIR

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 src/conf/virstorageobj.h     |  3 +++
 src/storage/storage_driver.c | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/src/conf/virstorageobj.h b/src/conf/virstorageobj.h
index 92d229f9b4..4547a0df9b 100644
--- a/src/conf/virstorageobj.h
+++ b/src/conf/virstorageobj.h
@@ -37,6 +37,9 @@ typedef virStorageDriverState *virStorageDriverStatePtr;
 struct _virStorageDriverState {
     virMutex lock;
 
+    /* pid file FD, ensures two copies of the driver can't use the same root */
+    int lockFD;
+
     virStoragePoolObjListPtr pools;
 
     char *configDir;
diff --git a/src/storage/storage_driver.c b/src/storage/storage_driver.c
index 496d51b1e0..03ac6a6845 100644
--- a/src/storage/storage_driver.c
+++ b/src/storage/storage_driver.c
@@ -43,6 +43,7 @@
 #include "virlog.h"
 #include "virfile.h"
 #include "virfdstream.h"
+#include "virpidfile.h"
 #include "configmake.h"
 #include "virsecret.h"
 #include "virstring.h"
@@ -256,6 +257,7 @@ storageStateInitialize(bool privileged,
     if (VIR_ALLOC(driver) < 0)
         return -1;
 
+    driver->lockFD = -1;
     if (virMutexInit(&driver->lock) < 0) {
         VIR_FREE(driver);
         return -1;
@@ -296,6 +298,11 @@ storageStateInitialize(bool privileged,
         goto error;
     }
 
+    if ((driver->lockFD =
+         virPidFileAcquire(driver->stateDir, "driver",
+                           true, getpid())) < 0)
+        goto error;
+
     if (virStoragePoolObjLoadAllState(driver->pools,
                                       driver->stateDir) < 0)
         goto error;
@@ -371,6 +378,10 @@ storageStateCleanup(void)
     /* free inactive pools */
     virObjectUnref(driver->pools);
 
+    if (driver->lockFD != -1)
+        virPidFileRelease(driver->stateDir, "driver",
+                          driver->lockFD);
+
     VIR_FREE(driver->configDir);
     VIR_FREE(driver->autostartDir);
     VIR_FREE(driver->stateDir);
-- 
2.21.0