libxl: add p2p migration

Introduce support for VIR_MIGRATE_PEER2PEER in libvirt migration.
Most of the changes occur at the source and no modifications at
the receiver.

In P2P mode there is only the Perform phase so we must handle the
connection with the destination and actually perform the
migration. libxlDomainPerformP2P implements the connection to the
destination and libxlDoMigrateP2P implements the actual migration
logic with virConnectPtr. In this function we take care of doing
all phases of migration in the destination similar to
virDomainMigrateVersion3Full. We appropriately save the last
error reported in each of the phases to provide proper reporting.
We don't yet support VIR_MIGRATE_TUNNELED and we always use V3
with extensible params, thus it also makes the implementation
simpler.

It is worth noting that the receiver didn't have any changes, and
since it's still the v3 sequence thus it is possible to migrate
from a P2P to non-P2P host.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>

src/libxl/libxl_driver.c

@@ -5009,6 +5009,7 @@ libxlConnectSupportsFeature(virConnectPtr conn, int feature)
     switch (feature) {
     case VIR_DRV_FEATURE_TYPED_PARAM_STRING:
     case VIR_DRV_FEATURE_MIGRATION_PARAMS:
+    case VIR_DRV_FEATURE_MIGRATION_P2P:
         return 1;
     default:
         return 0;
@@ -5334,9 +5335,15 @@ libxlDomainMigratePerform3Params(virDomainPtr dom,
     if (virDomainMigratePerform3ParamsEnsureACL(dom->conn, vm->def) < 0)
         goto cleanup;
 
-    if (libxlDomainMigrationPerform(driver, vm, dom_xml, dconnuri,
-                                    uri, dname, flags) < 0)
-        goto cleanup;
+    if (flags & VIR_MIGRATE_PEER2PEER) {
+        if (libxlDomainMigrationPerformP2P(driver, vm, dom->conn, dom_xml,
+                                           dconnuri, uri, dname, flags) < 0)
+            goto cleanup;
+    } else {
+        if (libxlDomainMigrationPerform(driver, vm, dom_xml, dconnuri,
+                                        uri, dname, flags) < 0)
+            goto cleanup;
+    }
 
     ret = 0;
 

src/libxl/libxl_migration.c

@@ -42,6 +42,7 @@
 #include "libxl_conf.h"
 #include "libxl_migration.h"
 #include "locking/domain_lock.h"
+#include "virtypedparam.h"
 
 #define VIR_FROM_THIS VIR_FROM_LIBXL
 
@@ -456,6 +457,202 @@ libxlDomainMigrationPrepare(virConnectPtr dconn,
     return ret;
 }
 
+/* This function is a simplification of virDomainMigrateVersion3Full
+ * excluding tunnel support and restricting it to migration v3
+ * with params since it was the first to be introduced in libxl.
+ */
+static int
+libxlDoMigrateP2P(libxlDriverPrivatePtr driver,
+                  virDomainObjPtr vm,
+                  virConnectPtr sconn,
+                  const char *xmlin,
+                  virConnectPtr dconn,
+                  const char *dconnuri ATTRIBUTE_UNUSED,
+                  const char *dname,
+                  const char *uri,
+                  unsigned int flags)
+{
+    virDomainPtr ddomain = NULL;
+    virTypedParameterPtr params = NULL;
+    int nparams = 0;
+    int maxparams = 0;
+    char *uri_out = NULL;
+    char *dom_xml = NULL;
+    unsigned long destflags;
+    bool cancelled = true;
+    virErrorPtr orig_err = NULL;
+    int ret = -1;
+
+    dom_xml = libxlDomainMigrationBegin(sconn, vm, xmlin);
+    if (!dom_xml)
+        goto cleanup;
+
+    if (virTypedParamsAddString(&params, &nparams, &maxparams,
+                                VIR_MIGRATE_PARAM_DEST_XML, dom_xml) < 0)
+        goto cleanup;
+
+    if (dname &&
+        virTypedParamsAddString(&params, &nparams, &maxparams,
+                                VIR_MIGRATE_PARAM_DEST_NAME, dname) < 0)
+        goto cleanup;
+
+    if (uri &&
+        virTypedParamsAddString(&params, &nparams, &maxparams,
+                                VIR_MIGRATE_PARAM_URI, uri) < 0)
+        goto cleanup;
+
+    /* We don't require the destination to have P2P support
+     * as it looks to be normal migration from the receiver perpective.
+     */
+    destflags = flags & ~(VIR_MIGRATE_PEER2PEER);
+
+    VIR_DEBUG("Prepare3");
+    virObjectUnlock(vm);
+    ret = dconn->driver->domainMigratePrepare3Params
+        (dconn, params, nparams, NULL, 0, NULL, NULL, &uri_out, destflags);
+    virObjectLock(vm);
+
+    if (ret == -1)
+        goto cleanup;
+
+    if (uri_out) {
+        if (virTypedParamsReplaceString(&params, &nparams,
+                                        VIR_MIGRATE_PARAM_URI, uri_out) < 0) {
+            orig_err = virSaveLastError();
+            goto finish;
+        }
+    } else {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("domainMigratePrepare3 did not set uri"));
+        goto finish;
+    }
+
+    VIR_DEBUG("Perform3 uri=%s", NULLSTR(uri_out));
+    ret = libxlDomainMigrationPerform(driver, vm, NULL, NULL,
+                                      uri_out, NULL, flags);
+
+    if (ret < 0)
+        orig_err = virSaveLastError();
+
+    cancelled = (ret < 0);
+
+ finish:
+    VIR_DEBUG("Finish3 ret=%d", ret);
+    if (virTypedParamsGetString(params, nparams,
+                                VIR_MIGRATE_PARAM_DEST_NAME, NULL) <= 0 &&
+        virTypedParamsReplaceString(&params, &nparams,
+                                    VIR_MIGRATE_PARAM_DEST_NAME,
+                                    vm->def->name) < 0) {
+        ddomain = NULL;
+    } else {
+        virObjectUnlock(vm);
+        ddomain = dconn->driver->domainMigrateFinish3Params
+            (dconn, params, nparams, NULL, 0, NULL, NULL,
+             destflags, cancelled);
+        virObjectLock(vm);
+    }
+
+    cancelled = (ddomain == NULL);
+
+    /* If Finish3Params set an error, and we don't have an earlier
+     * one we need to preserve it in case confirm3 overwrites
+     */
+    if (!orig_err)
+        orig_err = virSaveLastError();
+
+    VIR_DEBUG("Confirm3 cancelled=%d vm=%p", cancelled, vm);
+    ret = libxlDomainMigrationConfirm(driver, vm, flags, cancelled);
+
+    if (ret < 0)
+        VIR_WARN("Guest %s probably left in 'paused' state on source",
+                 vm->def->name);
+
+ cleanup:
+    if (ddomain) {
+        virObjectUnref(ddomain);
+        ret = 0;
+    } else {
+        ret = -1;
+    }
+
+    if (orig_err) {
+        virSetError(orig_err);
+        virFreeError(orig_err);
+    }
+
+    VIR_FREE(dom_xml);
+    VIR_FREE(uri_out);
+    virTypedParamsFree(params, nparams);
+    return ret;
+}
+
+static int virConnectCredType[] = {
+    VIR_CRED_AUTHNAME,
+    VIR_CRED_PASSPHRASE,
+};
+
+static virConnectAuth virConnectAuthConfig = {
+    .credtype = virConnectCredType,
+    .ncredtype = ARRAY_CARDINALITY(virConnectCredType),
+};
+
+/* On P2P mode there is only the Perform3 phase and we need to handle
+ * the connection with the destination libvirtd and perform the migration.
+ * Here we first tackle the first part of it, and libxlDoMigrationP2P handles
+ * the migration process with an established virConnectPtr to the destination.
+ */
+int
+libxlDomainMigrationPerformP2P(libxlDriverPrivatePtr driver,
+                               virDomainObjPtr vm,
+                               virConnectPtr sconn,
+                               const char *xmlin,
+                               const char *dconnuri,
+                               const char *uri_str ATTRIBUTE_UNUSED,
+                               const char *dname,
+                               unsigned int flags)
+{
+    int ret = -1;
+    bool useParams;
+    virConnectPtr dconn = NULL;
+    virErrorPtr orig_err = NULL;
+
+    virObjectUnlock(vm);
+    dconn = virConnectOpenAuth(dconnuri, &virConnectAuthConfig, 0);
+    virObjectLock(vm);
+
+    if (dconn == NULL) {
+        virReportError(VIR_ERR_OPERATION_FAILED,
+                       _("Failed to connect to remote libvirt URI %s: %s"),
+                       dconnuri, virGetLastErrorMessage());
+        return ret;
+    }
+
+    virObjectUnlock(vm);
+    useParams = VIR_DRV_SUPPORTS_FEATURE(dconn->driver, dconn,
+                                         VIR_DRV_FEATURE_MIGRATION_PARAMS);
+    virObjectLock(vm);
+
+    if (!useParams) {
+        virReportError(VIR_ERR_OPERATION_FAILED, "%s",
+                       _("Destination libvirt does not support migration with extensible parameters"));
+        goto cleanup;
+    }
+
+    ret = libxlDoMigrateP2P(driver, vm, sconn, xmlin, dconn, dconnuri,
+                            dname, uri_str, flags);
+
+ cleanup:
+    orig_err = virSaveLastError();
+    virObjectUnlock(vm);
+    virObjectUnref(dconn);
+    virObjectLock(vm);
+    if (orig_err) {
+        virSetError(orig_err);
+        virFreeError(orig_err);
+    }
+    return ret;
+}
+
 int
 libxlDomainMigrationPerform(libxlDriverPrivatePtr driver,
                             virDomainObjPtr vm,

src/libxl/libxl_migration.h

@@ -28,6 +28,7 @@
 
 # define LIBXL_MIGRATION_FLAGS                  \
     (VIR_MIGRATE_LIVE |                         \
+     VIR_MIGRATE_PEER2PEER |                    \
      VIR_MIGRATE_UNDEFINE_SOURCE |              \
      VIR_MIGRATE_PAUSED)
 
@@ -55,6 +56,16 @@ libxlDomainMigrationPrepare(virConnectPtr dconn,
                             char **uri_out,
                             unsigned int flags);
 
+int
+libxlDomainMigrationPerformP2P(libxlDriverPrivatePtr driver,
+                               virDomainObjPtr vm,
+                               virConnectPtr sconn,
+                               const char *dom_xml,
+                               const char *dconnuri,
+                               const char *uri_str,
+                               const char *dname,
+                               unsigned int flags);
+
 int
 libxlDomainMigrationPerform(libxlDriverPrivatePtr driver,
                             virDomainObjPtr vm,