[PATCH 6/7] qemu: use lighter-weight fd:n on incoming tunneled migration

[Eric Blake <eblake@xxxxxxxxxx>]

Outgoing migration still has to use a Unix socket and or exec netcat,
since there is no way to pass a migration fd into qemu via monitor
commands, but incoming migration need not suffer from the complexity.

* src/qemu/qemu_driver.c (qemudDomainMigratePrepareTunnel):
Replace Unix socket with simpler pipe.
Suggested by Paolo Bonzini.
---

I've since been corrected; qemu_monitor.c has qemuMonitorIOWriteWithFD
that looks like it can be used to avoid exec: on outgoing migrations
by instead passing an open fd over a unix socket, although I have not
tested that yet.  However, this patch does not need to be held up by
waiting for the followup patch that optimizes outgoing migrations.

 src/qemu/qemu_driver.c |   49 +++++++++++++++--------------------------------
 1 files changed, 16 insertions(+), 33 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index a82392e..8cb05b7 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -7925,11 +7925,10 @@ qemudDomainMigratePrepareTunnel(virConnectPtr dconn,
     struct qemud_driver *driver = dconn->privateData;
     virDomainDefPtr def = NULL;
     virDomainObjPtr vm = NULL;
-    char *migrateFrom;
     virDomainEventPtr event = NULL;
     int ret = -1;
     int internalret;
-    char *unixfile = NULL;
+    int dataFD[2] = { -1, -1 };
     unsigned long long qemuCmdFlags;
     qemuDomainObjPrivatePtr priv = NULL;
     struct timeval now;
@@ -7995,39 +7994,27 @@ qemudDomainMigratePrepareTunnel(virConnectPtr dconn,
     /* Domain starts inactive, even if the domain XML had an id field. */
     vm->def->id = -1;

-    if (virAsprintf(&unixfile, "%s/qemu.tunnelmigrate.dest.%s",
-                    driver->libDir, vm->def->name) < 0) {
-        virReportOOMError();
+    if (pipe(dataFD) < 0) {
+        virReportSystemError(errno, "%s",
+                             _("cannot create pipe for tunnelled migration"));
         goto endjob;
     }
-    unlink(unixfile);

     /* check that this qemu version supports the interactive exec */
-    if (qemuCapsExtractVersionInfo(vm->def->emulator, NULL, &qemuCmdFlags) < 0) {
+    if (qemuCapsExtractVersionInfo(vm->def->emulator, NULL,
+                                   &qemuCmdFlags) < 0) {
         qemuReportError(VIR_ERR_INTERNAL_ERROR,
                         _("Cannot determine QEMU argv syntax %s"),
                         vm->def->emulator);
         goto endjob;
     }
-    if (qemuCmdFlags & QEMUD_CMD_FLAG_MIGRATE_QEMU_UNIX)
-        internalret = virAsprintf(&migrateFrom, "unix:%s", unixfile);
-    else if (qemuCmdFlags & QEMUD_CMD_FLAG_MIGRATE_QEMU_EXEC)
-        internalret = virAsprintf(&migrateFrom, "exec:nc -U -l %s", unixfile);
-    else {
-        qemuReportError(VIR_ERR_OPERATION_FAILED,
-                        "%s", _("Destination qemu is too old to support tunnelled migration"));
-        goto endjob;
-    }
-    if (internalret < 0) {
-        virReportOOMError();
-        goto endjob;
-    }
+
     /* Start the QEMU daemon, with the same command-line arguments plus
-     * -incoming unix:/path/to/file or exec:nc -U /path/to/file
+     * -incoming stdin (which qemu_command might convert to exec:cat or fd:n)
      */
-    internalret = qemudStartVMDaemon(dconn, driver, vm, migrateFrom, true,
-                                     -1, NULL, VIR_VM_OP_MIGRATE_IN_START);
-    VIR_FREE(migrateFrom);
+    internalret = qemudStartVMDaemon(dconn, driver, vm, "stdin", true,
+                                     dataFD[1], NULL,
+                                     VIR_VM_OP_MIGRATE_IN_START);
     if (internalret < 0) {
         qemuDomainStartAudit(vm, "migrated", false);
         /* Note that we don't set an error here because qemudStartVMDaemon
@@ -8040,9 +8027,7 @@ qemudDomainMigratePrepareTunnel(virConnectPtr dconn,
         goto endjob;
     }

-    if (virFDStreamConnectUNIX(st,
-                               unixfile,
-                               false) < 0) {
+    if (virFDStreamOpen(st, dataFD[0]) < 0) {
         qemuDomainStartAudit(vm, "migrated", false);
         qemudShutdownVMDaemon(driver, vm, 0);
         if (!vm->persistent) {
@@ -8050,9 +8035,8 @@ qemudDomainMigratePrepareTunnel(virConnectPtr dconn,
                 virDomainRemoveInactive(&driver->domains, vm);
             vm = NULL;
         }
-        virReportSystemError(errno,
-                             _("cannot open unix socket '%s' for tunnelled migration"),
-                             unixfile);
+        virReportSystemError(errno, "%s",
+                             _("cannot pass pipe for tunnelled migration"));
         goto endjob;
     }

@@ -8082,9 +8066,8 @@ endjob:

 cleanup:
     virDomainDefFree(def);
-    if (unixfile)
-        unlink(unixfile);
-    VIR_FREE(unixfile);
+    VIR_FORCE_CLOSE(dataFD[0]);
+    VIR_FORCE_CLOSE(dataFD[1]);
     if (vm)
         virDomainObjUnlock(vm);
     if (event)
-- 
1.7.3.4

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