Re: [PATCH 1/2] vfio: Don't be a iterable and legacy device at the same time

[Peter Xu]

On Thu, Jun 22, 2023 at 01:22:26PM +0200, Lukas Straub wrote:
> Legacy savevm devices only implement save_state() and load_state().
> Iterable devices shouldn't implement save_state() or else they are
> handled both as an iterable and legacy device in the savevm code.
> 
> Signed-off-by: Lukas Straub 
> ---
> 
> Note: this patch is completely untested.

PS: if you're not confident on the change will always work, better mark as
rfc to show a proposal of such change.

Comparing to the "legacy" vs "modern" migration, IIUC it was about whether
to use vmsd, so it's "save_state()" vs "vmsd" in that regard.

Personally, I don't immediately see a direct conflict / issue with device
providing both save_state() and save_setup().  It means the device declares
both (1) iterable data, and (2) non-iterable data (which can be either vmsd
or save_state()).

I do think vmsd is still preferred here for (2), e.g., I quickly looked at
vmstate_vfio_pci_config which seems fine to be implemented as a vmsd, with
a post_load() perhaps.  But that's another story.  It just all looks still
fine.

Do we get any benefit from having that restriction?

-- 
Peter Xu

[PATCH 1/2] vfio: Don't be a iterable and legacy device at the same time

[Lukas Straub]

Legacy savevm devices only implement save_state() and load_state().
Iterable devices shouldn't implement save_state() or else they are
handled both as an iterable and legacy device in the savevm code.

Signed-off-by: Lukas Straub 
---

Note: this patch is completely untested.

 hw/vfio/migration.c | 38 +++---
 1 file changed, 11 insertions(+), 27 deletions(-)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 6b58dddb88..8d7f22dbd3 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -166,23 +166,6 @@ static int vfio_load_buffer(QEMUFile *f, VFIODevice 
*vbasedev,
 return ret;
 }
 
-static int vfio_save_device_config_state(QEMUFile *f, void *opaque)
-{
-VFIODevice *vbasedev = opaque;
-
-qemu_put_be64(f, VFIO_MIG_FLAG_DEV_CONFIG_STATE);
-
-if (vbasedev->ops && vbasedev->ops->vfio_save_config) {
-vbasedev->ops->vfio_save_config(vbasedev, f);
-}
-
-qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
-
-trace_vfio_save_device_config_state(vbasedev->name);
-
-return qemu_file_get_error(f);
-}
-
 static int vfio_load_device_config_state(QEMUFile *f, void *opaque)
 {
 VFIODevice *vbasedev = opaque;
@@ -351,7 +334,6 @@ static int vfio_save_complete_precopy(QEMUFile *f, void 
*opaque)
 }
 } while (!ret);
 
-qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
 ret = qemu_file_get_error(f);
 if (ret) {
 return ret;
@@ -365,20 +347,23 @@ static int vfio_save_complete_precopy(QEMUFile *f, void 
*opaque)
VFIO_DEVICE_STATE_ERROR);
 trace_vfio_save_complete_precopy(vbasedev->name, ret);
 
-return ret;
-}
+qemu_put_be64(f, VFIO_MIG_FLAG_DEV_CONFIG_STATE);
 
-static void vfio_save_state(QEMUFile *f, void *opaque)
-{
-VFIODevice *vbasedev = opaque;
-int ret;
+if (vbasedev->ops && vbasedev->ops->vfio_save_config) {
+vbasedev->ops->vfio_save_config(vbasedev, f);
+}
+
+qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE);
+
+trace_vfio_save_device_config_state(vbasedev->name);
 
-ret = vfio_save_device_config_state(f, opaque);
+ret = qemu_file_get_error(f);
 if (ret) {
 error_report("%s: Failed to save device config space",
  vbasedev->name);
-qemu_file_set_error(f, ret);
 }
+
+return ret;
 }
 
 static int vfio_load_setup(QEMUFile *f, void *opaque)
@@ -458,7 +443,6 @@ static const SaveVMHandlers savevm_vfio_handlers = {
 .save_cleanup = vfio_save_cleanup,
 .state_pending_exact = vfio_state_pending_exact,
 .save_live_complete_precopy = vfio_save_complete_precopy,
-.save_state = vfio_save_state,
 .load_setup = vfio_load_setup,
 .load_cleanup = vfio_load_cleanup,
 .load_state = vfio_load_state,
-- 
2.39.2



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