1:56 a.m.
in the previous version, I mentioned the scenario of long-term pause while
writing external memory checkpoints:
v1: https://www.redhat.com/archives/libvir-list/2016-August/msg01194.html
Daniel suggested not to hardcode the flag, but wire this upto the API. When
the user invokes the snapshot they can request the
VIR_DOMAIN_SAVE_BYPASS_CACHE flag explicitly. So in this version I
introduce the --bypass-cache option in libvirt snapshot API. When invoking
an external VM snapshots, we may use the command like this:
virsh snapshot-create-as VM snap --memspec /path/to/memsnap --live
--bypass-cache
The VM snapshot can be done with inapparent VM suspend now. Without
"--bypass-cache" flag, one may experience long-term VM suspend (so that the
implication of "--live" option is not significant), provided that the VM
has a large amount of dirty pages to save.
Signed-off-by: fuweiwei <fuweiwei2(a)huawei.com>
---
include/libvirt/libvirt-domain-snapshot.h | 3 +++
src/qemu/qemu_driver.c | 20 ++++++++++++++++++--
tools/virsh-snapshot.c | 12 ++++++++++++
3 files changed, 33 insertions(+), 2 deletions(-)
diff --git a/include/libvirt/libvirt-domain-snapshot.h
b/include/libvirt/libvirt-domain-snapshot.h
index 0f73f24..aeff665 100644
--- a/include/libvirt/libvirt-domain-snapshot.h
+++ b/include/libvirt/libvirt-domain-snapshot.h
@@ -70,6 +70,9 @@ typedef enum {
VIR_DOMAIN_SNAPSHOT_CREATE_LIVE = (1 << 8), /* create the snapshot
while the guest is
running */
+ VIR_DOMAIN_SNAPSHOT_CREATE_BYPASS_CACHE = (1 << 9), i/* Bypass cache
+ while writing external
+ checkpoint files. */
} virDomainSnapshotCreateFlags;
/* Take a snapshot of the current VM state */
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 2089359..d5f441f 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -14036,6 +14036,7 @@ qemuDomainSnapshotCreateActiveExternal(virConnectPtr conn,
bool pmsuspended = false;
virQEMUDriverConfigPtr cfg = NULL;
int compressed = QEMU_SAVE_FORMAT_RAW;
+ unsigned int save_memory_flag = 0;
/* If quiesce was requested, then issue a freeze command, and a
* counterpart thaw command when it is actually sent to agent.
@@ -14116,8 +14117,12 @@ qemuDomainSnapshotCreateActiveExternal(virConnectPtr conn,
if (!(xml = qemuDomainDefFormatLive(driver, vm->def, true, true)))
goto cleanup;
+ if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_BYPASS_CACHE)
+ save_memory_flag |= VIR_DOMAIN_SAVE_BYPASS_CACHE;
+
if ((ret = qemuDomainSaveMemory(driver, vm, snap->def->file,
- xml, compressed, resume, 0,
+ xml, compressed, resume,
+ save_memory_flag,
QEMU_ASYNC_JOB_SNAPSHOT)) < 0)
goto cleanup;
@@ -14224,7 +14229,8 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT |
VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE |
VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC |
- VIR_DOMAIN_SNAPSHOT_CREATE_LIVE, NULL);
+ VIR_DOMAIN_SNAPSHOT_CREATE_LIVE |
+ VIR_DOMAIN_SNAPSHOT_CREATE_BYPASS_CACHE, NULL);
VIR_REQUIRE_FLAG_RET(VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE,
VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY,
@@ -14297,6 +14303,16 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
goto cleanup;
}
+ /* the option of bypass cache is only supported for external checkpoints */
+ if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_BYPASS_CACHE &&
+ (def->memory != VIR_DOMAIN_SNAPSHOT_LOCATION_EXTERNAL ||
+ redefine)) {
+ virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+ _("only external memory snapshots support "
+ "cache bypass."));
+ goto cleanup;
+ }
+
/* allow snapshots only in certain states */
switch ((virDomainState) vm->state.state) {
/* valid states */
diff --git a/tools/virsh-snapshot.c b/tools/virsh-snapshot.c
index f879e7a..0627baf 100644
--- a/tools/virsh-snapshot.c
+++ b/tools/virsh-snapshot.c
@@ -160,6 +160,10 @@ static const vshCmdOptDef opts_snapshot_create[] = {
.type = VSH_OT_BOOL,
.help = N_("require atomic operation")
},
+ {.name = "bypass-cache",
+ .type = VSH_OT_BOOL,
+ .help = N_("bypass system cache while writing external checkpoints")
+ },
VIRSH_COMMON_OPT_LIVE(N_("take a live snapshot")),
{.name = NULL}
};
@@ -191,6 +195,8 @@ cmdSnapshotCreate(vshControl *ctl, const vshCmd *cmd)
flags |= VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC;
if (vshCommandOptBool(cmd, "live"))
flags |= VIR_DOMAIN_SNAPSHOT_CREATE_LIVE;
+ if (vshCommandOptBool(cmd, "bypass-cache"))
+ flags |= VIR_DOMAIN_SNAPSHOT_CREATE_BYPASS_CACHE;
if (!(dom = virshCommandOptDomain(ctl, cmd, NULL)))
goto cleanup;
@@ -358,6 +364,10 @@ static const vshCmdOptDef opts_snapshot_create_as[] = {
.type = VSH_OT_BOOL,
.help = N_("require atomic operation")
},
+ {.name = "bypass-cache",
+ .type = VSH_OT_BOOL,
+ .help = N_("bypass system cache while writing external checkpoints")
+ },
VIRSH_COMMON_OPT_LIVE(N_("take a live snapshot")),
{.name = "memspec",
.type = VSH_OT_STRING,
@@ -404,6 +414,8 @@ cmdSnapshotCreateAs(vshControl *ctl, const vshCmd *cmd)
flags |= VIR_DOMAIN_SNAPSHOT_CREATE_ATOMIC;
if (vshCommandOptBool(cmd, "live"))
flags |= VIR_DOMAIN_SNAPSHOT_CREATE_LIVE;
+ if (vshCommandOptBool(cmd, "bypass-cache"))
+ flags |= VIR_DOMAIN_SNAPSHOT_CREATE_BYPASS_CACHE;
if (!(dom = virshCommandOptDomain(ctl, cmd, NULL)))
return false;
--
1.9.5.msysgit.1