qemu: add support for running QEMU driver in embedded mode

This enables support for running QEMU embedded to the calling
application process using a URI:

   qemu:///embed?root=/some/path

Note that it is important to keep the path reasonably short to
avoid risk of hitting the limit on UNIX socket path names
which is 108 characters.

When using the embedded mode with a root=/var/tmp/embed, the
driver will use the following paths:

                logDir: /var/tmp/embed/log/qemu
           swtpmLogDir: /var/tmp/embed/log/swtpm
         configBaseDir: /var/tmp/embed/etc/qemu
              stateDir: /var/tmp/embed/run/qemu
         swtpmStateDir: /var/tmp/embed/run/swtpm
              cacheDir: /var/tmp/embed/cache/qemu
                libDir: /var/tmp/embed/lib/qemu
       swtpmStorageDir: /var/tmp/embed/lib/swtpm
 defaultTLSx509certdir: /var/tmp/embed/etc/pki/qemu

These are identical whether the embedded driver is privileged
or unprivileged.

This compares with the system instance which uses

                logDir: /var/log/libvirt/qemu
           swtpmLogDir: /var/log/swtpm/libvirt/qemu
         configBaseDir: /etc/libvirt/qemu
              stateDir: /run/libvirt/qemu
         swtpmStateDir: /run/libvirt/qemu/swtpm
              cacheDir: /var/cache/libvirt/qemu
                libDir: /var/lib/libvirt/qemu
       swtpmStorageDir: /var/lib/libvirt/swtpm
 defaultTLSx509certdir: /etc/pki/qemu

At this time all features present in the QEMU driver are available when
running in embedded mode, availability matching whether the embedded
driver is privileged or unprivileged.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

docs/drvqemu.html.in

@@ -63,6 +63,105 @@ qemu+tcp://example.com/system        (remote access, SASl/Kerberos)
 qemu+ssh://root@example.com/system   (remote access, SSH tunnelled)
 </pre>
 
+    <h3><a id="uriembedded">Embedded driver</a></h3>
+
+    <p>
+      Since 6.0.0 the QEMU driver has experimental support for operating
+      in an embedded mode. In this scenario, rather than connecting to
+      the libvirtd daemon, the QEMU driver runs in the client application
+      process directly. To use this the client application must have
+      registered &amp; be running an instance of the event loop. To open
+      the driver in embedded mode the app use the new URI path and specify
+      a virtual root directory under which the driver will create content.
+    </p>
+
+    <pre>
+      qemu:///embed?root=/some/dir
+    </pre>
+
+    <p>
+      Broadly speaking the range of functionality is intended to be
+      on a par with that seen when using the traditional system or
+      session libvirt connections to QEMU. The features will of course
+      differ depending on whether the application using the embedded
+      driver is running privileged or unprivileged. For example PCI
+      device assignment or TAP based networking are only available
+      when running privileged. While the embedded mode is still classed
+      as experimental some features may change their default settings
+      between releases.
+    </p>
+
+    <p>
+      By default if the application uses any APIs associated with
+      secondary drivers, these will result in a connection being
+      opened to the corresponding driver in libvirtd. For example,
+      this allows a virtual machine from the embedded QEMU to connect
+      its NIC to a virtual network or connect its disk to a storage
+      volume. Some of the secondary drivers will also be able to support
+      running in embedded mode. Currently this is supported by the
+      secrets driver, to allow for use of VMs with encrypted disks
+    </p>
+
+    <h4><a id="embedTree">Directory tree</a></h4>
+
+    <p>
+      Under the specified root directory the following locations will
+      be used
+    </p>
+
+    <pre>
+/some/dir
+  |
+  +- log
+  |   |
+  |   +- qemu
+  |   +- swtpm
+  |
+  +- etc
+  |   |
+  |   +- qemu
+  |   +- pki
+  |       |
+  |       +- qemu
+  |
+  +- run
+  |   |
+  |   +- qemu
+  |   +- swtpm
+  |
+  +- cache
+  |   |
+  |   +- qemu
+  |
+  +- lib
+      |
+      +- qemu
+      +- swtpm
+    </pre>
+
+    <p>
+      Note that UNIX domain sockets used for QEMU virtual machines had
+      a maximum filename length of 108 characters. Bear this in mind
+      when picking a root directory to avoid risk of exhausting the
+      filename space. The application is responsible for recursively
+      purging the contents of this directory tree once they no longer
+      require a connection, though it can also be left intact for reuse
+      when opening a future connection.
+    </p>
+
+    <h4><a id="embedAPI">API usage with event loop></a></h4>
+
+    <p>
+      To use the QEMU driver in embedded mode the application must
+      register an event loop with libvirt. Many of the QEMU driver
+      API calls will rely on the event loop processing data. With this
+      in mind, applications must <strong>NEVER</strong> invoke API
+      calls from the event loop thread itself, only other threads.
+      Not following this rule will lead to deadlocks in the API.
+      This restriction is intended to be lifted in a future release
+      of libvirt, once QMP processing moves to a dedicated thread.
+    </p>
+
     <h2><a id="security">Driver security architecture</a></h2>
 
     <p>

src/qemu/qemu_conf.c

@@ -104,7 +104,8 @@ qemuDriverUnlock(virQEMUDriverPtr driver)
 #endif
 
 
-virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged)
+virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged,
+                                              const char *root)
 {
     g_autoptr(virQEMUDriverConfig) cfg = NULL;
 
@@ -114,7 +115,11 @@ virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged)
     if (!(cfg = virObjectNew(virQEMUDriverConfigClass)))
         return NULL;
 
-    cfg->uri = privileged ? "qemu:///system" : "qemu:///session";
+    if (root) {
+        cfg->uri = g_strdup_printf("qemu:///embed?root=%s", root);
+    } else {
+        cfg->uri = g_strdup(privileged ? "qemu:///system" : "qemu:///session");
+    }
 
     if (privileged) {
         if (virGetUserID(QEMU_USER, &cfg->user) < 0)
@@ -130,7 +135,24 @@ virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged)
 
     cfg->cgroupControllers = -1; /* -1 == auto-detect */
 
-    if (privileged) {
+    if (root != NULL) {
+        cfg->logDir = g_strdup_printf("%s/log/qemu", root);
+        cfg->swtpmLogDir = g_strdup_printf("%s/log/swtpm", root);
+        cfg->configBaseDir = g_strdup_printf("%s/etc", root);
+        cfg->stateDir = g_strdup_printf("%s/run/qemu", root);
+        cfg->swtpmStateDir = g_strdup_printf("%s/run/swtpm", root);
+        cfg->cacheDir = g_strdup_printf("%s/cache/qemu", root);
+        cfg->libDir = g_strdup_printf("%s/lib/qemu", root);
+        cfg->swtpmStorageDir = g_strdup_printf("%s/lib/swtpm", root);
+
+        cfg->saveDir = g_strdup_printf("%s/save", cfg->libDir);
+        cfg->snapshotDir = g_strdup_printf("%s/snapshot", cfg->libDir);
+        cfg->checkpointDir = g_strdup_printf("%s/checkpoint", cfg->libDir);
+        cfg->autoDumpPath = g_strdup_printf("%s/dump", cfg->libDir);
+        cfg->channelTargetDir = g_strdup_printf("%s/channel/target", cfg->libDir);
+        cfg->nvramDir = g_strdup_printf("%s/nvram", cfg->libDir);
+        cfg->memoryBackingDir = g_strdup_printf("%s/ram", cfg->libDir);
+    } else if (privileged) {
         cfg->logDir = g_strdup_printf("%s/log/libvirt/qemu", LOCALSTATEDIR);
 
         cfg->swtpmLogDir = g_strdup_printf("%s/log/swtpm/libvirt/qemu",
@@ -189,6 +211,16 @@ virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged)
         cfg->memoryBackingDir = g_strdup_printf("%s/qemu/ram", cfg->configBaseDir);
         cfg->swtpmStorageDir = g_strdup_printf("%s/qemu/swtpm",
                                                cfg->configBaseDir);
+    }
+
+    if (privileged) {
+        if (!virDoesUserExist("tss") ||
+            virGetUserID("tss", &cfg->swtpm_user) < 0)
+            cfg->swtpm_user = 0; /* fall back to root */
+        if (!virDoesGroupExist("tss") ||
+            virGetGroupID("tss", &cfg->swtpm_group) < 0)
+            cfg->swtpm_group = 0; /* fall back to root */
+    } else {
         cfg->swtpm_user = (uid_t)-1;
         cfg->swtpm_group = (gid_t)-1;
     }
@@ -201,7 +233,11 @@ virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged)
      * This will then be used as a fallback if the service specific
      * directory doesn't exist (although we don't check if this exists).
      */
-    cfg->defaultTLSx509certdir = g_strdup(SYSCONFDIR "/pki/qemu");
+    if (root == NULL) {
+        cfg->defaultTLSx509certdir = g_strdup(SYSCONFDIR "pki/qemu");
+    } else {
+        cfg->defaultTLSx509certdir = g_strdup_printf("%s/etc/pki/qemu", root);
+    }
 
     cfg->vncListen = g_strdup(VIR_LOOPBACK_IPV4_ADDR);
     cfg->spiceListen = g_strdup(VIR_LOOPBACK_IPV4_ADDR);
@@ -264,6 +300,7 @@ static void virQEMUDriverConfigDispose(void *obj)
     virBitmapFree(cfg->namespaces);
 
     virStringListFree(cfg->cgroupDeviceACL);
+    VIR_FREE(cfg->uri);
 
     VIR_FREE(cfg->configBaseDir);
     VIR_FREE(cfg->configDir);

src/qemu/qemu_conf.h

@@ -75,7 +75,7 @@ typedef virQEMUDriverConfig *virQEMUDriverConfigPtr;
 struct _virQEMUDriverConfig {
     virObject parent;
 
-    const char *uri;
+    char *uri;
 
     uid_t user;
     gid_t group;
@@ -240,8 +240,9 @@ struct _virQEMUDriver {
     /* Atomic inc/dec only */
     unsigned int nactive;
 
-    /* Immutable value */
+    /* Immutable values */
     bool privileged;
+    char *embeddedRoot;
 
     /* Immutable pointers. Caller must provide locking */
     virStateInhibitCallback inhibitCallback;
@@ -313,7 +314,8 @@ struct _virQEMUDriver {
     virHashAtomicPtr migrationErrors;
 };
 
-virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged);
+virQEMUDriverConfigPtr virQEMUDriverConfigNew(bool privileged,
+                                              const char *root);
 
 int virQEMUDriverConfigLoadFile(virQEMUDriverConfigPtr cfg,
                                 const char *filename,

src/qemu/qemu_driver.c

@@ -645,12 +645,6 @@ qemuStateInitialize(bool privileged,
     const char *defsecmodel = NULL;
     g_autofree virSecurityManagerPtr *sec_managers = NULL;
 
-    if (root != NULL) {
-        virReportError(VIR_ERR_INVALID_ARG, "%s",
-                       _("Driver does not support embedded mode"));
-        return -1;
-    }
-
     if (VIR_ALLOC(qemu_driver) < 0)
         return VIR_DRV_STATE_INIT_ERROR;
 
@@ -668,6 +662,8 @@ qemuStateInitialize(bool privileged,
 
     qemu_driver->privileged = privileged;
     qemu_driver->hostarch = virArchFromHost();
+    if (root != NULL)
+        qemu_driver->embeddedRoot = g_strdup(root);
 
     if (!(qemu_driver->domains = virDomainObjListNew()))
         goto error;
@@ -681,7 +677,7 @@ qemuStateInitialize(bool privileged,
     if (privileged)
         qemu_driver->hostsysinfo = virSysinfoRead();
 
-    if (!(qemu_driver->config = cfg = virQEMUDriverConfigNew(privileged)))
+    if (!(qemu_driver->config = cfg = virQEMUDriverConfigNew(privileged, root)))
         goto error;
 
     if (!(driverConf = g_strdup_printf("%s/qemu.conf", cfg->configBaseDir)))
@@ -1185,10 +1181,30 @@ static virDrvOpenStatus qemuConnectOpen(virConnectPtr conn,
         return VIR_DRV_OPEN_ERROR;
     }
 
+    if (qemu_driver->embeddedRoot) {
+        const char *root = virURIGetParam(conn->uri, "root");
+        if (!root)
+            return VIR_DRV_OPEN_ERROR;
+
+        if (STRNEQ(conn->uri->path, "/embed")) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("URI must be qemu:///embed"));
+            return VIR_DRV_OPEN_ERROR;
+        }
+
+        if (STRNEQ(root, qemu_driver->embeddedRoot)) {
+            virReportError(VIR_ERR_INTERNAL_ERROR,
+                           _("Cannot open embedded driver at path '%s', "
+                             "already open with path '%s'"),
+                           root, qemu_driver->embeddedRoot);
+            return VIR_DRV_OPEN_ERROR;
+        }
+    } else {
         if (!virConnectValidateURIPath(conn->uri->path,
                                        "qemu",
                                        virQEMUDriverIsPrivileged(qemu_driver)))
             return VIR_DRV_OPEN_ERROR;
+    }
 
     if (virConnectOpenEnsureACL(conn) < 0)
         return VIR_DRV_OPEN_ERROR;
@@ -23416,6 +23432,7 @@ static virHypervisorDriver qemuHypervisorDriver = {
 static virConnectDriver qemuConnectDriver = {
     .localOnly = true,
     .uriSchemes = (const char *[]){ "qemu", NULL },
+    .embeddable = true,
     .hypervisorDriver = &qemuHypervisorDriver,
 };
 

src/qemu/qemu_process.c

@@ -6683,11 +6683,18 @@ qemuProcessLaunch(virConnectPtr conn,
 
     cfg = virQEMUDriverGetConfig(driver);
 
-    if ((flags & VIR_QEMU_PROCESS_START_AUTODESTROY) && !conn) {
+    if (flags & VIR_QEMU_PROCESS_START_AUTODESTROY) {
+        if (!conn) {
             virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
                            _("Domain autodestroy requires a connection handle"));
             return -1;
         }
+        if (driver->embeddedRoot) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("Domain autodestroy not supported for embedded drivers yet"));
+            return -1;
+        }
+    }
 
     hookData.vm = vm;
     hookData.driver = driver;

tests/domaincapstest.c

@@ -369,7 +369,7 @@ mymain(void)
 #endif
 
 #if WITH_QEMU
-    virQEMUDriverConfigPtr cfg = virQEMUDriverConfigNew(false);
+    virQEMUDriverConfigPtr cfg = virQEMUDriverConfigNew(false, "");
 
     if (!cfg)
         return EXIT_FAILURE;

tests/testutilsqemu.c

@@ -380,8 +380,7 @@ int qemuTestDriverInit(virQEMUDriver *driver)
         return -1;
 
     driver->hostarch = virArchFromHost();
-
+    driver->config = virQEMUDriverConfigNew(false, "");
-    driver->config = virQEMUDriverConfigNew(false);
     if (!driver->config)
         goto error;