[libvirt] [PATCH 2/2] blockjob: wire up online qemu block-commit

[Eric Blake]

This is the bare minimum to kick off a block commit.  In particular,
flags support is missing (shallow requires us to crawl the backing
chain to determine the file name to pass to the qemu monitor command;
delete requires us to track what needs to be deleted at the time
the completion event fires), and top must be non-NULL (matching the
fact that the current qemu code does not support committing the
active layer, although it is still planned to add that before 1.3).
Since the active layer won't change, we have it easy and do not have
to alter the domain XML.  We are also relying on qemu to do some
error detection on our behalf (such as validating 'top' and 'base'
as being members of the backing chain).  Additionally, this will
fail if SELinux is enforcing, because we fail to grant qemu proper
read/write access to the files it will be modifying.

* src/qemu/qemu_driver.c (qemuDomainBlockCommit): New function.
(qemuDriver): Register it.
---
 src/qemu/qemu_driver.c | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index fddb446..137df7e 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -12529,6 +12529,84 @@ qemuDomainBlockPull(virDomainPtr dom, const char *path, unsigned long bandwidth,
     return qemuDomainBlockRebase(dom, path, NULL, bandwidth, flags);
 }

+
+static int
+qemuDomainBlockCommit(virDomainPtr dom, const char *path, const char *base,
+                      const char *top, unsigned long bandwidth,
+                      unsigned int flags)
+{
+    struct qemud_driver *driver = dom->conn->privateData;
+    qemuDomainObjPrivatePtr priv;
+    virDomainObjPtr vm = NULL;
+    char *device = NULL;
+    int ret = -1;
+    virDomainEventPtr event = NULL;
+    int idx;
+    virDomainDiskDefPtr disk;
+
+    virCheckFlags(0, -1);
+
+    if (!(vm = qemuDomObjFromDomain(dom)))
+        goto cleanup;
+    priv = vm->privateData;
+
+    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0)
+        goto cleanup;
+
+    if (!virDomainObjIsActive(vm)) {
+        virReportError(VIR_ERR_OPERATION_INVALID,
+                       "%s", _("domain is not running"));
+        goto endjob;
+    }
+    if (!qemuCapsGet(priv->caps, QEMU_CAPS_BLOCK_COMMIT) || !top) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                       _("online commit of active image not supported with "
+                         "this QEMU binary"));
+        goto endjob;
+    }
+
+    device = qemuDiskPathToAlias(vm, path, &idx);
+    if (!device)
+        goto endjob;
+    disk = vm->def->disks[idx];
+
+    if (!disk->src) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("disk %s has no source file to be committed"),
+                       disk->dst);
+        goto endjob;
+    }
+
+    /* XXX For now, we are relying on qemu to check that 'top' and
+     * 'base' resolve to members of the backing chain in correct
+     * order; but if we ever get more paranoid and track the backing
+     * chain ourself, we should be pre-validating the data rather than
+     * relying on qemu.  For that matter, we need to be changing the
+     * SELinux label on both 'base' and the parent of 'top', so that
+     * qemu can open(O_RDWR) those files for the duration of the
+     * commit.  */
+    qemuDomainObjEnterMonitor(driver, vm);
+    ret = qemuMonitorBlockCommit(priv->mon, device, top, base, bandwidth);
+    qemuDomainObjExitMonitor(driver, vm);
+
+endjob:
+    if (qemuDomainObjEndJob(driver, vm) == 0) {
+        vm = NULL;
+        goto cleanup;
+    }
+
+cleanup:
+    VIR_FREE(device);
+    if (vm)
+        virDomainObjUnlock(vm);
+    if (event) {
+        qemuDriverLock(driver);
+        qemuDomainEventQueue(driver, event);
+        qemuDriverUnlock(driver);
+    }
+    return ret;
+}
+
 static int
 qemuDomainOpenGraphics(virDomainPtr dom,
                        unsigned int idx,
@@ -13871,6 +13949,7 @@ static virDriver qemuDriver = {
     .domainBlockJobSetSpeed = qemuDomainBlockJobSetSpeed, /* 0.9.4 */
     .domainBlockPull = qemuDomainBlockPull, /* 0.9.4 */
     .domainBlockRebase = qemuDomainBlockRebase, /* 0.9.10 */
+    .domainBlockCommit = qemuDomainBlockCommit, /* 0.10.3 */
     .isAlive = qemuIsAlive, /* 0.9.8 */
     .nodeSuspendForDuration = nodeSuspendForDuration, /* 0.9.8 */
     .domainSetBlockIoTune = qemuDomainSetBlockIoTune, /* 0.9.8 */
-- 
1.7.11.4