Re: [PATCH v5 22/23] migration: Add error-parameterized function variants in VMSD struct

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Jul 17, 2025 at 06:07:45AM +0530, Arun Menon wrote:
> - We need to have good error reporting in the callbacks in
>   VMStateDescription struct. Specifically pre_save, post_save,
>   pre_load and post_load callbacks.
> - It is not possible to change these functions everywhere in one
>   patch, therefore, we introduce a duplicate set of callbacks
>   with Error object passed to them.
> - So, in this commit, we implement 'errp' variants of these callbacks,
>   introducing an explicit Error object parameter.
> - This is a functional step towards transitioning the entire codebase
>   to the new error-parameterized functions.
> - Deliberately called in mutual exclusion from their counterparts,
>   to prevent conflicts during the transition.
> - New impls should preferentally use 'errp' variants of
>   these methods, and existing impls incrementally converted.
>   The variants without 'errp' are intended to be removed
>   once all usage is converted.
> 
> Signed-off-by: Arun Menon <armenon@redhat.com>
> ---
>  include/migration/vmstate.h | 11 +++++++++++
>  migration/vmstate.c         | 36 +++++++++++++++++++++++++++++++-----
>  2 files changed, 42 insertions(+), 5 deletions(-)


> @@ -524,7 +542,9 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
>                  if (ret) {
>                      error_setg(errp, "Save of field %s/%s failed",
>                                  vmsd->name, field->name);
> -                    if (vmsd->post_save) {
> +                    if (vmsd->post_save_errp) {
> +                        vmsd->post_save_errp(opaque, errp);

We are already in an error path here, and we set 'errp' just a few lines
above. If post_save_errp tries to set it too, then we're doomed.

You'll need to pass an &Local_err in here, and then append it to the
current error.

> +                    } else if (vmsd->post_save) {
>                          vmsd->post_save(opaque);
>                      }
>                      return ret;
> @@ -552,7 +572,13 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
>  
>      ret = vmstate_subsection_save(f, vmsd, opaque, vmdesc, errp);


Potentially set 'errp'



> -    if (vmsd->post_save) {
> +    if (vmsd->post_save_errp) {
> +        int ps_ret = vmsd->post_save_errp(opaque, errp);

so must not be passing 'errp' here.

> +        if (!ret && ps_ret) {
> +            ret = ps_ret;
> +            error_prepend(errp, "post-save failed: %s ", vmsd->name);
> +        }


> +    } else if (vmsd->post_save) {
>          int ps_ret = vmsd->post_save(opaque);
>          if (!ret && ps_ret) {
>              ret = ps_ret;
> 
> -- 
> 2.50.0
> 
> 

With regards,
Daniel
-- 
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