nodedev: acquire a pidfile in the driver root directory

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/nodedev/driver.pid

In unprivileged libvirtd this ends up locking

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

NB, the latter can vary depending on $XDG_RUNTIME_DIR

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/conf/virnodedeviceobj.h

@@ -37,6 +37,11 @@ typedef virNodeDeviceDriverState *virNodeDeviceDriverStatePtr;
 struct _virNodeDeviceDriverState {
     virMutex lock;
 
+    /* pid file FD, ensures two copies of the driver can't use the same root */
+    int lockFD;
+
+    char *stateDir;
+
     virNodeDeviceObjListPtr devs;       /* currently-known devices */
     void *privateData;                  /* driver-specific private data */
     bool privileged;                    /* whether we run in privileged mode */

src/node_device/node_device_hal.c

@@ -33,10 +33,13 @@
 #include "viralloc.h"
 #include "viruuid.h"
 #include "virpci.h"
+#include "virpidfile.h"
 #include "virlog.h"
 #include "virdbus.h"
 #include "virstring.h"
 
+#include "configmake.h"
+
 #define VIR_FROM_THIS VIR_FROM_NODEDEV
 
 VIR_LOG_INIT("node_device.node_device_hal");
@@ -606,12 +609,36 @@ nodeStateInitialize(bool privileged ATTRIBUTE_UNUSED,
     if (VIR_ALLOC(driver) < 0)
         return -1;
 
+    driver->lockFD = -1;
     if (virMutexInit(&driver->lock) < 0) {
         VIR_FREE(driver);
         return -1;
     }
     nodeDeviceLock();
 
+    if (privileged) {
+        if (virAsprintf(&driver->stateDir,
+                        "%s/run/libvirt/nodedev", LOCALSTATEDIR) < 0)
+            goto failure;
+    } else {
+        VIR_AUTOFREE(char *) rundir = NULL;
+
+        if (!(rundir = virGetUserRuntimeDirectory()))
+            goto failure;
+        if (virAsprintf(&driver->stateDir, "%s/nodedev/run", rundir) < 0)
+            goto failure;
+    }
+
+    if (virFileMakePathWithMode(driver->stateDir, S_IRWXU) < 0) {
+        virReportSystemError(errno, _("cannot create state directory '%s'"),
+                             driver->stateDir);
+        goto failure;
+    }
+
+    if ((driver->lockFD =
+         virPidFileAcquire(driver->stateDir, "driver", true, getpid())) < 0)
+        goto failure;
+
     if (!(driver->devs = virNodeDeviceObjListNew()))
         goto failure;
 
@@ -708,6 +735,10 @@ nodeStateCleanup(void)
         virNodeDeviceObjListFree(driver->devs);
         (void)libhal_ctx_shutdown(hal_ctx, NULL);
         (void)libhal_ctx_free(hal_ctx);
+        if (driver->lockFD != -1)
+            virPidFileRelease(driver->stateDir, "driver", driver->lockFD);
+
+        VIR_FREE(driver->stateDir);
         nodeDeviceUnlock();
         virMutexDestroy(&driver->lock);
         VIR_FREE(driver);

src/node_device/node_device_udev.c

@@ -38,10 +38,13 @@
 #include "virbuffer.h"
 #include "virfile.h"
 #include "virpci.h"
+#include "virpidfile.h"
 #include "virstring.h"
 #include "virnetdev.h"
 #include "virmdev.h"
 
+#include "configmake.h"
+
 #define VIR_FROM_THIS VIR_FROM_NODEDEV
 
 VIR_LOG_INIT("node_device.node_device_udev");
@@ -1494,6 +1497,11 @@ nodeStateCleanup(void)
     virObjectUnref(driver->nodeDeviceEventState);
 
     virNodeDeviceObjListFree(driver->devs);
+
+    if (driver->lockFD != -1)
+        virPidFileRelease(driver->stateDir, "driver", driver->lockFD);
+
+    VIR_FREE(driver->stateDir);
     virMutexDestroy(&driver->lock);
     VIR_FREE(driver);
 
@@ -1810,6 +1818,7 @@ nodeStateInitialize(bool privileged,
     if (VIR_ALLOC(driver) < 0)
         return -1;
 
+    driver->lockFD = -1;
     if (virMutexInit(&driver->lock) < 0) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("Unable to initialize mutex"));
@@ -1819,6 +1828,29 @@ nodeStateInitialize(bool privileged,
 
     driver->privileged = privileged;
 
+    if (privileged) {
+        if (virAsprintf(&driver->stateDir,
+                        "%s/run/libvirt/nodedev", LOCALSTATEDIR) < 0)
+            goto cleanup;
+    } else {
+        VIR_AUTOFREE(char *) rundir = NULL;
+
+        if (!(rundir = virGetUserRuntimeDirectory()))
+            goto cleanup;
+        if (virAsprintf(&driver->stateDir, "%s/nodedev/run", rundir) < 0)
+            goto cleanup;
+    }
+
+    if (virFileMakePathWithMode(driver->stateDir, S_IRWXU) < 0) {
+        virReportSystemError(errno, _("cannot create state directory '%s'"),
+                             driver->stateDir);
+        goto cleanup;
+    }
+
+    if ((driver->lockFD =
+         virPidFileAcquire(driver->stateDir, "driver", true, getpid())) < 0)
+        goto cleanup;
+
     if (!(driver->devs = virNodeDeviceObjListNew()) ||
         !(priv = udevEventDataNew()))
         goto cleanup;