[libvirt RFC] add API for parallel Saves (not for committing)

[Claudio Fontana]

RFC, starting point for discussion.

Sketch API changes to allow parallel Saves, and open up
and implementation for QEMU to leverage multifd migration to files,
with optional multifd compression.

This allows to improve save times for huge VMs.

The idea is to issue commands like:

virsh save domain /path/savevm --parallel --parallel-connections 2

and have libvirt start a multifd migration to:

/path/savevm   : main migration connection
/path/savevm.1 : multifd channel 1
/path/savevm.2 : multifd channel 2

Signed-off-by: Claudio Fontana <cfontana at suse.de>
---
 include/libvirt/libvirt-domain.h | 5 +++++
 src/driver-hypervisor.h          | 7 +++++++
 src/libvirt_public.syms          | 5 +++++
 src/qemu/qemu_driver.c           | 1 +
 tools/virsh-domain.c             | 8 ++++++++
 5 files changed, 26 insertions(+)

diff --git a/include/libvirt/libvirt-domain.h b/include/libvirt/libvirt-domain.h
index 2d5718301e..a7b9c4132d 100644
--- a/include/libvirt/libvirt-domain.h
+++ b/include/libvirt/libvirt-domain.h
@@ -1270,6 +1270,7 @@ typedef enum {
     VIR_DOMAIN_SAVE_RUNNING      = 1 << 1, /* Favor running over paused */
     VIR_DOMAIN_SAVE_PAUSED       = 1 << 2, /* Favor paused over running */
     VIR_DOMAIN_SAVE_RESET_NVRAM  = 1 << 3, /* Re-initialize NVRAM from template */
+    VIR_DOMAIN_SAVE_PARALLEL     = 1 << 4, /* Parallel Save/Restore to multiple files */
 } virDomainSaveRestoreFlags;
 
 int                     virDomainSave           (virDomainPtr domain,
@@ -1278,6 +1279,10 @@ int                     virDomainSaveFlags      (virDomainPtr domain,
                                                  const char *to,
                                                  const char *dxml,
                                                  unsigned int flags);
+int                     virDomainSaveParametersFlags (virDomainPtr domain,
+                                                      virTypedParameterPtr params,
+                                                      int nparams,
+                                                      unsigned int flags);
 int                     virDomainRestore        (virConnectPtr conn,
                                                  const char *from);
 int                     virDomainRestoreFlags   (virConnectPtr conn,
diff --git a/src/driver-hypervisor.h b/src/driver-hypervisor.h
index 4423eb0885..a4e1d21e76 100644
--- a/src/driver-hypervisor.h
+++ b/src/driver-hypervisor.h
@@ -240,6 +240,12 @@ typedef int
                          const char *dxml,
                          unsigned int flags);
 
+typedef int
+(*virDrvDomainSaveParametersFlags)(virDomainPtr domain,
+                                   virTypedParameterPtr params,
+                                   int nparams,
+                                   unsigned int flags);
+
 typedef int
 (*virDrvDomainRestore)(virConnectPtr conn,
                        const char *from);
@@ -1489,6 +1495,7 @@ struct _virHypervisorDriver {
     virDrvDomainGetControlInfo domainGetControlInfo;
     virDrvDomainSave domainSave;
     virDrvDomainSaveFlags domainSaveFlags;
+    virDrvDomainSaveParametersFlags domainSaveParametersFlags;
     virDrvDomainRestore domainRestore;
     virDrvDomainRestoreFlags domainRestoreFlags;
     virDrvDomainSaveImageGetXMLDesc domainSaveImageGetXMLDesc;
diff --git a/src/libvirt_public.syms b/src/libvirt_public.syms
index f93692c427..eb3a7afb75 100644
--- a/src/libvirt_public.syms
+++ b/src/libvirt_public.syms
@@ -916,4 +916,9 @@ LIBVIRT_8.0.0 {
         virDomainSetLaunchSecurityState;
 } LIBVIRT_7.8.0;
 
+LIBVIRT_8.3.0 {
+    global:
+        virDomainSaveParametersFlags;
+} LIBVIRT_8.0.0;
+
 # .... define new API here using predicted next version number ....
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 77012eb527..249105356c 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -20826,6 +20826,7 @@ static virHypervisorDriver qemuHypervisorDriver = {
     .domainGetControlInfo = qemuDomainGetControlInfo, /* 0.9.3 */
     .domainSave = qemuDomainSave, /* 0.2.0 */
     .domainSaveFlags = qemuDomainSaveFlags, /* 0.9.4 */
+    .domainSaveParametersFlags = qemuDomainSaveParametersFlags, /* 8.3.0 */
     .domainRestore = qemuDomainRestore, /* 0.2.0 */
     .domainRestoreFlags = qemuDomainRestoreFlags, /* 0.9.4 */
     .domainSaveImageGetXMLDesc = qemuDomainSaveImageGetXMLDesc, /* 0.9.4 */
diff --git a/tools/virsh-domain.c b/tools/virsh-domain.c
index d5fd8be7c3..ccded6d265 100644
--- a/tools/virsh-domain.c
+++ b/tools/virsh-domain.c
@@ -4164,6 +4164,14 @@ static const vshCmdOptDef opts_save[] = {
      .type = VSH_OT_BOOL,
      .help = N_("avoid file system cache when saving")
     },
+    {.name = "parallel",
+     .type = VSH_OT_BOOL,
+     .help = N_("enable parallel save to files")
+    },
+    {.name = "parallel-connections",
+     .type = VSH_OT_INT,
+     .help = N_("number of connections/files for parallel save")
+    },
     {.name = "xml",
      .type = VSH_OT_STRING,
      .completer = virshCompletePathLocalExisting,
-- 
2.34.1