[libvirt] [PATCH v3 09/12] qemu: Start PR daemon on domain startup

[Michal Privoznik]

Before we exec() qemu we have to spawn pr-helper processes for
all managed reservations (well, technically there can only one).
The only caveat there is that we should place the process into
the same namespace and cgroup as qemu (so that it shares the same
view of the system). But we can do that only after we've forked.
That means calling the setup function between fork() and exec().

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_process.c | 169 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 169 insertions(+)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 57c06c7c1..b876d293a 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2551,6 +2551,169 @@ qemuProcessResctrlCreate(virQEMUDriverPtr driver,
     ret = 0;
  cleanup:
     virObjectUnref(caps);
+
+    return ret;
+}
+
+
+static void
+qemuProcessKillPRDaemon(virDomainObjPtr vm)
+{
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+
+    if (priv->prPid == (pid_t) -1)
+        return;
+
+    virProcessKillPainfully(priv->prPid, true);
+    priv->prPid = (pid_t) -1;
+}
+
+
+static int
+qemuProcessSetupOnePRDaemonHook(void *opaque)
+{
+    virDomainObjPtr vm = opaque;
+    size_t i, nfds = 0;
+    int *fds = NULL;
+    int ret = -1;
+
+    if (virProcessGetNamespaces(vm->pid, &nfds, &fds) < 0)
+        return ret;
+
+    if (nfds > 0 &&
+        virProcessSetNamespaces(nfds, fds) < 0)
+        goto cleanup;
+
+    ret = 0;
+ cleanup:
+    for (i = 0; i < nfds; i++)
+        VIR_FORCE_CLOSE(fds[i]);
+    VIR_FREE(fds);
+    return ret;
+}
+
+
+static int
+qemuProcessSetupOnePRDaemon(virDomainObjPtr vm,
+                            virDomainDiskDefPtr disk)
+{
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+    virQEMUDriverPtr driver = priv->driver;
+    virQEMUDriverConfigPtr cfg;
+    qemuDomainStorageSourcePrivatePtr srcPriv;
+    qemuDomainDiskPRDPtr prd;
+    char *pidfile = NULL;
+    pid_t cpid = -1;
+    virCommandPtr cmd = NULL;
+    virTimeBackOffVar timebackoff;
+    const unsigned long long timeout = 500000; /* ms */
+    int ret = -1;
+
+    if (priv->prPid != (pid_t) -1 ||
+        !virStoragePRDefIsManaged(disk->src->pr))
+        return 0;
+
+    cfg = virQEMUDriverGetConfig(driver);
+    srcPriv = QEMU_DOMAIN_STORAGE_SOURCE_PRIVATE(disk->src);
+    prd = srcPriv->prd;
+
+    if (!virFileIsExecutable(cfg->prHelperName)) {
+        virReportSystemError(errno, _("'%s' is not a suitable pr helper"),
+                             cfg->prHelperName);
+        goto cleanup;
+    }
+
+    if (!(pidfile = virPidFileBuildPath(cfg->stateDir, prd->alias)))
+        goto cleanup;
+
+    if (unlink(pidfile) < 0 &&
+        errno != ENOENT) {
+        virReportSystemError(errno,
+                             _("Cannot remove stale PID file %s"),
+                             pidfile);
+        goto cleanup;
+    }
+
+    if (!(cmd = virCommandNewArgList(cfg->prHelperName,
+                                     "-k", prd->path,
+                                     NULL)))
+        goto cleanup;
+
+    virCommandDaemonize(cmd);
+    virCommandSetPidFile(cmd, pidfile);
+    /* The only caveat there is that we should place the process
+     * into the same namespace and cgroup as qemu (so that it
+     * shares the same view of the system). */
+    virCommandSetPreExecHook(cmd, qemuProcessSetupOnePRDaemonHook, vm);
+
+    if (virCommandRun(cmd, NULL) < 0)
+        goto cleanup;
+
+    if (virPidFileReadPath(pidfile, &cpid) < 0) {
+        virReportError(VIR_ERR_INTERNAL_ERROR,
+                       _("pr helper %s didn't show up"), prd->alias);
+        goto cleanup;
+    }
+
+    if (virTimeBackOffStart(&timebackoff, 1, timeout) < 0)
+        goto cleanup;
+    while (virTimeBackOffWait(&timebackoff)) {
+        if (virFileExists(prd->path))
+            break;
+
+        if (virProcessKill(cpid, 0) == 0)
+            continue;
+
+        virReportSystemError(errno,
+                             _("pr helper %s died unexpectedly"), prd->alias);
+        goto cleanup;
+    }
+
+    if (priv->cgroup &&
+        virCgroupAddMachineTask(priv->cgroup, cpid) < 0)
+        goto cleanup;
+
+    if (qemuSecurityDomainSetPathLabel(driver->securityManager,
+                                       vm->def, prd->path, true) < 0)
+        goto cleanup;
+
+    priv->prPid = cpid;
+    ret = 0;
+ cleanup:
+    if (ret < 0) {
+        virCommandAbort(cmd);
+        virProcessKillPainfully(cpid, true);
+    }
+    virCommandFree(cmd);
+    if (pidfile) {
+        if (unlink(pidfile) < 0 &&
+            errno != ENOENT &&
+            !virGetLastError())
+            virReportSystemError(errno,
+                                 _("Cannot remove stale PID file %s"),
+                                 pidfile);
+        VIR_FREE(pidfile);
+    }
+    virObjectUnref(cfg);
+    return ret;
+}
+
+
+static int
+qemuProcessSetupPRDaemon(virDomainObjPtr vm)
+{
+    size_t i;
+    int ret = -1;
+
+    for (i = 0; i < vm->def->ndisks; i++) {
+        if (qemuProcessSetupOnePRDaemon(vm, vm->def->disks[i]) < 0)
+            goto cleanup;
+    }
+
+    ret = 0;
+ cleanup:
+    if (ret < 0)
+        qemuProcessKillPRDaemon(vm);
     return ret;
 }
 
@@ -6065,6 +6228,10 @@ qemuProcessLaunch(virConnectPtr conn,
     if (qemuProcessResctrlCreate(driver, vm) < 0)
         goto cleanup;
 
+    VIR_DEBUG("Setting up PR daemon");
+    if (qemuProcessSetupPRDaemon(vm) < 0)
+        goto cleanup;
+
     VIR_DEBUG("Setting domain security labels");
     if (qemuSecuritySetAllLabel(driver,
                                 vm,
@@ -6645,6 +6812,8 @@ void qemuProcessStop(virQEMUDriverPtr driver,
         VIR_FREE(vm->def->seclabels[i]->imagelabel);
     }
 
+    qemuProcessKillPRDaemon(vm);
+
     qemuHostdevReAttachDomainDevices(driver, vm->def);
 
     def = vm->def;
-- 
2.16.1