qemu: command: Refactor qemuBuildDriveStrValidate to make qemuCaps optional

To allow merging this with other disk type checks we need to check
qemuCaps only when available, since some of the checks are executed on
disk cold-plug and thus capabilities should not be checked.

Make the checks optional by making them conditional on qemuCaps not
being NULL.

src/qemu/qemu_command.c

@@ -1553,31 +1553,6 @@ qemuBuildDriveStrValidate(virDomainDiskDefPtr disk,
         return -1;
     }
 
-    if (disk->serial &&
-        virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_SERIAL)) {
-        if (disk->bus == VIR_DOMAIN_DISK_BUS_SCSI &&
-            disk->device == VIR_DOMAIN_DISK_DEVICE_LUN) {
-            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                           _("scsi-block 'lun' devices do not support the "
-                             "serial property"));
-            return -1;
-        }
-    }
-
-    if (disk->cachemode == VIR_DOMAIN_DISK_CACHE_DIRECTSYNC &&
-        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_CACHE_DIRECTSYNC)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("disk cache mode 'directsync' is not supported by this QEMU"));
-        return -1;
-    }
-
-    if (disk->cachemode == VIR_DOMAIN_DISK_CACHE_UNSAFE &&
-        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_CACHE_UNSAFE)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("disk cache mode 'unsafe' is not supported by this QEMU"));
-        return -1;
-    }
-
     if (disk->iomode == VIR_DOMAIN_DISK_IO_NATIVE &&
         disk->cachemode != VIR_DOMAIN_DISK_CACHE_DIRECTSYNC &&
         disk->cachemode != VIR_DOMAIN_DISK_CACHE_DISABLE) {
@@ -1588,32 +1563,59 @@ qemuBuildDriveStrValidate(virDomainDiskDefPtr disk,
         return -1;
     }
 
-    if (disk->copy_on_read &&
-        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_COPY_ON_READ)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("copy_on_read is not supported by this QEMU binary"));
-        return -1;
-    }
+    if (qemuCaps) {
+        if (disk->serial &&
+            virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_SERIAL)) {
+            if (disk->bus == VIR_DOMAIN_DISK_BUS_SCSI &&
+                disk->device == VIR_DOMAIN_DISK_DEVICE_LUN) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("scsi-block 'lun' devices do not support the "
+                                 "serial property"));
+                return -1;
+            }
+        }
 
-    if (disk->discard &&
-        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_DISCARD)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("discard is not supported by this QEMU binary"));
-        return -1;
-    }
+        if (disk->cachemode == VIR_DOMAIN_DISK_CACHE_DIRECTSYNC &&
+            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_CACHE_DIRECTSYNC)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("disk cache mode 'directsync' is not supported by this QEMU"));
+            return -1;
+        }
 
-    if (disk->detect_zeroes &&
-        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_DETECT_ZEROES)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("detect_zeroes is not supported by this QEMU binary"));
-        return -1;
-    }
+        if (disk->cachemode == VIR_DOMAIN_DISK_CACHE_UNSAFE &&
+            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_CACHE_UNSAFE)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("disk cache mode 'unsafe' is not supported by this QEMU"));
+            return -1;
+        }
 
-    if (disk->iomode &&
-        !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_AIO)) {
-        virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                       _("disk aio mode not supported with this QEMU binary"));
-        return -1;
+        if (disk->copy_on_read &&
+            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_COPY_ON_READ)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("copy_on_read is not supported by this QEMU binary"));
+            return -1;
+        }
+
+        if (disk->discard &&
+            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_DISCARD)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("discard is not supported by this QEMU binary"));
+            return -1;
+        }
+
+        if (disk->detect_zeroes &&
+            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_DETECT_ZEROES)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("detect_zeroes is not supported by this QEMU binary"));
+            return -1;
+        }
+
+        if (disk->iomode &&
+            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_AIO)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("disk aio mode not supported with this QEMU binary"));
+            return -1;
+        }
     }
 
     return 0;