[PATCH v2 2/7] qemu: Introduce functions to handle transient disk

[Masayoshi Mizuma <msys.mizuma@xxxxxxxxx>]

From: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>

Here is the implementation of transient option for qcow2 and raw format
disk. This gets available <transient/> directive in domain xml file
like as:

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/guest.qcow2'/>
      <target dev='vda' bus='virtio'/>
      <transient/>
    </disk>

When the qemu command line options are built, a new qcow2 image is
created with backing qcow2 by using blockdev-snapshot command.
The backing image is the qcow2 file which is set as <source>.
The filename of the new qcow2 image is original-source-file.TRANSIENT.

Signed-off-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx>
---
 src/qemu/qemu_snapshot.c  | 134 ++++++++++++++++++++++++++++++++++++++
 src/qemu/qemu_snapshot.h  |   8 +++
 src/util/virstoragefile.h |   2 +
 3 files changed, 144 insertions(+)

diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
index d310e6ff02..5c61d19f26 100644
--- a/src/qemu/qemu_snapshot.c
+++ b/src/qemu/qemu_snapshot.c
@@ -2265,3 +2265,137 @@ qemuSnapshotDelete(virDomainObjPtr vm,
  cleanup:
     return ret;
 }
+
+static int
+qemuTransientDiskPrepareOne(virQEMUDriverPtr driver,
+                            virDomainObjPtr vm,
+                            qemuSnapshotDiskDataPtr data,
+                            virHashTablePtr blockNamedNodeData,
+                            int asyncJob,
+                            virJSONValuePtr actions)
+{
+    int rc = -1;
+    virStorageSourcePtr dest;
+    virStorageSourcePtr src = data->disk->src;
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+    g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(priv->driver);
+
+    if (!strlen(src->path))
+        return rc;
+
+    if (!(dest = virStorageSourceNew()))
+        return rc;
+
+    dest->path = g_strdup_printf("%s.TRANSIENT", src->path);
+
+    if (virFileExists(dest->path)) {
+        virReportError(VIR_ERR_INVALID_ARG,
+                       _("Transient disk '%s' for '%s' exists"),
+                       dest->path, src->path);
+        goto cleanup;
+    }
+
+    dest->type = VIR_STORAGE_TYPE_FILE;
+    dest->format = VIR_STORAGE_FILE_QCOW2;
+    data->src = dest;
+
+    if (qemuSnapshotDiskPrepareOne(driver, vm, cfg, data->disk,
+                                         NULL, data, blockNamedNodeData,
+                                         false, true, asyncJob, actions) < 0)
+        goto cleanup;
+
+    rc = 0;
+ cleanup:
+    if (rc < 0)
+        g_free(dest->path);
+
+    return rc;
+}
+
+static int
+qemuWaitTransaction(virQEMUDriverPtr driver,
+                    virDomainObjPtr vm,
+                    int asyncJob,
+                    virJSONValuePtr *actions)
+{
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+
+    if (qemuDomainObjEnterMonitorAsync(driver, vm, asyncJob) < 0)
+        return -1;
+
+    if (qemuMonitorTransaction(priv->mon, actions) < 0)
+        return -1;
+
+    if (qemuDomainObjExitMonitor(driver, vm) < 0)
+        return -1;
+
+    return 0;
+}
+
+int
+qemuTransientCreatetDisk(virQEMUDriverPtr driver,
+                         virDomainObjPtr vm,
+                         int asyncJob)
+{
+    size_t i;
+    int rc = -1;
+    size_t ndata = 0;
+    qemuSnapshotDiskDataPtr data = NULL;
+    g_autoptr(virJSONValue) actions = NULL;
+    qemuDomainObjPrivatePtr priv = vm->privateData;
+    g_autoptr(virHashTable) blockNamedNodeData = NULL;
+    bool blockdev =  virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV);
+
+    if (!blockdev)
+        return rc;
+
+    if (VIR_ALLOC_N(data, vm->def->ndisks) < 0)
+        return rc;
+
+    if (!(blockNamedNodeData = qemuBlockGetNamedNodeData(vm, asyncJob)))
+        goto cleanup;
+
+    if (!(actions = virJSONValueNewArray()))
+        goto cleanup;
+
+    for (i = 0; i < vm->def->ndisks; i++) {
+        virDomainDiskDefPtr disk = vm->def->disks[i];
+
+        if (disk->src->readonly)
+            continue;
+
+        if (disk->transient) {
+            data[ndata].disk = disk;
+            if (qemuTransientDiskPrepareOne(driver, vm, &data[ndata], blockNamedNodeData,
+                                                 asyncJob, actions) < 0)
+                goto cleanup;
+            ndata++;
+        }
+    }
+
+    if (qemuWaitTransaction(driver, vm, asyncJob, &actions) < 0)
+        goto cleanup;
+
+    for (i = 0; i < ndata; i++) {
+        qemuSnapshotDiskDataPtr dd = &data[i];
+
+        qemuSnapshotDiskUpdateSource(driver, vm, dd, blockdev);
+        dd->disk->src->transientEstablished = true;
+    }
+
+    VIR_FREE(data);
+    rc = 0;
+ cleanup:
+    qemuSnapshotDiskCleanup(data, vm->def->ndisks, driver, vm, asyncJob);
+
+    return rc;
+}
+
+void
+qemuTransientRemoveDisk(virDomainDiskDefPtr disk)
+{
+    if (disk->src->transientEstablished) {
+        VIR_DEBUG("unlink transient disk: %s", disk->src->path);
+        unlink(disk->src->path);
+    }
+}
diff --git a/src/qemu/qemu_snapshot.h b/src/qemu/qemu_snapshot.h
index 8b3ebe87b1..aecb1762d2 100644
--- a/src/qemu/qemu_snapshot.h
+++ b/src/qemu/qemu_snapshot.h
@@ -53,3 +53,11 @@ int
 qemuSnapshotDelete(virDomainObjPtr vm,
                    virDomainSnapshotPtr snapshot,
                    unsigned int flags);
+
+int
+qemuTransientCreatetDisk(virQEMUDriverPtr driver,
+                         virDomainObjPtr vm,
+                         int asyncJob);
+
+void
+qemuTransientRemoveDisk(virDomainDiskDefPtr disk);
diff --git a/src/util/virstoragefile.h b/src/util/virstoragefile.h
index f73b3ee005..fd42d017f3 100644
--- a/src/util/virstoragefile.h
+++ b/src/util/virstoragefile.h
@@ -383,6 +383,8 @@ struct _virStorageSource {
     /* these must not be used apart from formatting the output JSON in the qemu driver */
     char *ssh_user;
     bool ssh_host_key_check_disabled;
+
+    bool transientEstablished;
 };
 
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(virStorageSource, virObjectUnref);
-- 
2.27.0