[libvirt] [PATCH 01/12] qemu: 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/qemu/driver.pid

In unprivileged libvirtd this ends up locking

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

NB, the latter can vary depending on $XDG_RUNTIME_DIR

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 src/qemu/qemu_conf.h   | 3 +++
 src/qemu/qemu_driver.c | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
index e51514a344..2229b76e89 100644
--- a/src/qemu/qemu_conf.h
+++ b/src/qemu/qemu_conf.h
@@ -221,6 +221,9 @@ struct _virQEMUDriver {
      * then lockless thereafter */
     virQEMUDriverConfigPtr config;
 
+    /* pid file FD, ensures two copies of the driver can't use the same root */
+    int lockFD;
+
     /* Immutable pointer, self-locking APIs */
     virThreadPoolPtr workerPool;
 
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 5a75f23981..8bc069d3e2 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -70,6 +70,7 @@
 #include "node_device_conf.h"
 #include "virpci.h"
 #include "virusb.h"
+#include "virpidfile.h"
 #include "virprocess.h"
 #include "libvirt_internal.h"
 #include "virxml.h"
@@ -587,6 +588,8 @@ qemuStateInitialize(bool privileged,
     if (VIR_ALLOC(qemu_driver) < 0)
         return -1;
 
+    qemu_driver->lockFD = -1;
+
     if (virMutexInit(&qemu_driver->lock) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("cannot initialize mutex"));
@@ -673,6 +676,10 @@ qemuStateInitialize(bool privileged,
         goto error;
     }
 
+    if ((qemu_driver->lockFD =
+         virPidFileAcquire(cfg->stateDir, "driver", true, getpid())) < 0)
+        goto error;
+
     qemu_driver->qemuImgBinary = virFindFileInPath("qemu-img");
 
     if (!(qemu_driver->lockManager =
@@ -1032,6 +1039,8 @@ qemuStateCleanup(void)
     if (!qemu_driver)
         return -1;
 
+    if (qemu_driver->lockFD != -1)
+        virPidFileRelease(qemu_driver->config->stateDir, "driver", qemu_driver->lockFD);
     virThreadPoolFree(qemu_driver->workerPool);
     virObjectUnref(qemu_driver->config);
     virObjectUnref(qemu_driver->hostdevMgr);
-- 
2.21.0