[libvirt] [PATCHv5 13/13] qemu: support fd: migration with compression

[Eric Blake]

Spawn the compressor ourselves, instead of requiring the shell.

* src/qemu/qemu_migration.c (qemuMigrationToFile): Spawn
compression helper process when needed.
---

v5: rebase to changes in 11/13, add a cloexec, rely on recent
virCommand changes to actually clean up the intermediate compressor
process, actually test this time

It's a minor shame that virCommandSetOutputFD can create an output
pipe and return the fd, but virCommandSetInputFD cannot do likewise
(this patch has to create its own pipe).  On the other hand, by
creating our own pipe, this patch didn't fall foul of the cloexec bug
that had to first be fixed on the restore path in 2/13.

 src/qemu/qemu_migration.c |   38 ++++++++++++++++++++++++++++++++++----
 1 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index 2803de6..98b9d01 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -1298,9 +1298,11 @@ qemuMigrationToFile(struct qemud_driver *driver, virDomainObjPtr vm,
     int ret = -1;
     int rc;
     bool restoreLabel = false;
+    virCommandPtr cmd = NULL;
+    int pipeFD[2] = { -1, -1 };

     if (qemuCaps && qemuCapsGet(qemuCaps, QEMU_CAPS_MIGRATE_QEMU_FD) &&
-        !compressor) {
+        (!compressor || pipe(pipeFD) == 0)) {
         /* All right! We can use fd migration, which means that qemu
          * doesn't have to open() the file, so we don't have to futz
          * around with granting access or revoking it later.  */
@@ -1359,9 +1361,31 @@ qemuMigrationToFile(struct qemud_driver *driver, virDomainObjPtr vm,
             "-c",
             NULL
         };
-        rc = qemuMonitorMigrateToFile(priv->mon,
-                                      QEMU_MONITOR_MIGRATE_BACKGROUND,
-                                      args, path, offset);
+        if (pipeFD[0] != -1) {
+            cmd = virCommandNewArgs(args);
+            virCommandSetInputFD(cmd, pipeFD[0]);
+            virCommandSetOutputFD(cmd, &fd);
+            if (virSetCloseExec(pipeFD[1]) < 0) {
+                virReportSystemError(errno, "%s",
+                                     _("Unable to set cloexec flag"));
+                qemuDomainObjExitMonitorWithDriver(driver, vm);
+                goto cleanup;
+            }
+            if (virCommandRunAsync(cmd, NULL) < 0) {
+                qemuDomainObjExitMonitorWithDriver(driver, vm);
+                goto cleanup;
+            }
+            rc = qemuMonitorMigrateToFd(priv->mon,
+                                        QEMU_MONITOR_MIGRATE_BACKGROUND,
+                                        pipeFD[1]);
+            if (VIR_CLOSE(pipeFD[0]) < 0 ||
+                VIR_CLOSE(pipeFD[1]) < 0)
+                VIR_WARN0("failed to close intermediate pipe");
+        } else {
+            rc = qemuMonitorMigrateToFile(priv->mon,
+                                          QEMU_MONITOR_MIGRATE_BACKGROUND,
+                                          args, path, offset);
+        }
     }
     qemuDomainObjExitMonitorWithDriver(driver, vm);

@@ -1373,9 +1397,15 @@ qemuMigrationToFile(struct qemud_driver *driver, virDomainObjPtr vm,
     if (rc < 0)
         goto cleanup;

+    if (cmd && virCommandWait(cmd, NULL) < 0)
+        goto cleanup;
+
     ret = 0;

 cleanup:
+    VIR_FORCE_CLOSE(pipeFD[0]);
+    VIR_FORCE_CLOSE(pipeFD[1]);
+    virCommandFree(cmd);
     if (restoreLabel && (!bypassSecurityDriver) &&
         virSecurityManagerRestoreSavedStateLabel(driver->securityManager,
                                                  vm, path) < 0)
-- 
1.7.4