[libvirt] [RFC PATCH 1/2] qemu: caps: Add capability for dynamic 'auto-read-only' support for files

[Peter Krempa]

Initial implementation of 'auto-read-only' didn't reopen the backing
files when needed. For '-blockdev' to work we need to be able to tel
qemu to open a file read-only and change it during blockjobs as we label
backing chains with a sVirt label which does not allow writing. The
dynamic auto-read-only supports this as it reopens files when writing
is demanded.

Add a capability to detect that the posix file based backends support
the dynamic part.

Signed-off-by: Peter Krempa <pkrempa at redhat.com>
Reviewed-by: Jiri Denemark <jdenemar at redhat.com>
---
 src/qemu/qemu_capabilities.c                     | 2 ++
 src/qemu/qemu_capabilities.h                     | 1 +
 tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml | 1 +
 3 files changed, 4 insertions(+)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index c9677315ab..83b1a12d14 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -537,6 +537,7 @@ VIR_ENUM_IMPL(virQEMUCaps,
               /* 335 */
               "bochs-display",
               "migration-file-drop-cache",
+              "blockdev-file-dynamic-auto-read-only",
     );


@@ -1281,6 +1282,7 @@ static struct virQEMUCapsStringFlags virQEMUCapsQMPSchemaQueries[] = {
     { "query-display-options/ret-type/+egl-headless/rendernode", QEMU_CAPS_EGL_HEADLESS_RENDERNODE },
     { "nbd-server-add/arg-type/bitmap", QEMU_CAPS_NBD_BITMAP },
     { "blockdev-add/arg-type/+file/drop-cache", QEMU_CAPS_MIGRATION_FILE_DROP_CACHE },
+    { "blockdev-add/arg-type/+file/$dynamic-auto-read-only", QEMU_CAPS_BLOCK_FILE_AUTO_READONLY_DYNAMIC },
 };

 typedef struct _virQEMUCapsObjectTypeProps virQEMUCapsObjectTypeProps;
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index 68ef6c49b4..2fe0e26ced 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -518,6 +518,7 @@ typedef enum { /* virQEMUCapsFlags grouping marker for syntax-check */
     /* 335 */
     QEMU_CAPS_DEVICE_BOCHS_DISPLAY, /* -device bochs-display */
     QEMU_CAPS_MIGRATION_FILE_DROP_CACHE, /* migration with disk cache on is safe for type='file' disks */
+    QEMU_CAPS_BLOCK_FILE_AUTO_READONLY_DYNAMIC, /* the auto-read-only property of block backends for files is dynamic */

     QEMU_CAPS_LAST /* this must always be the last item */
 } virQEMUCapsFlags;
diff --git a/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml b/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml
index f4583d7fe7..fbde4f3a5d 100644
--- a/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml
+++ b/tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml
@@ -209,6 +209,7 @@
   <flag name='canonical-cpu-features'/>
   <flag name='bochs-display'/>
   <flag name='migration-file-drop-cache'/>
+  <flag name='blockdev-file-dynamic-auto-read-only'/>
   <version>4000050</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>43100759</microcodeVersion>
-- 
2.21.0