On Fri, Mar 13, 2026 at 03:12:14PM +0100, Alexander Mikhalitsyn wrote:
> From: Alexander Mikhalitsyn <[email protected]>
> 
> Let's introduce vmstate_{load,save}_field() helpers, they will
> be used in next patches to support fully-dynamic arrays with NULLs.
> 
> Signed-off-by: Alexander Mikhalitsyn <[email protected]>

Feel free to rebase to Vladimir's series here, Fabiano already queued it:

https://lore.kernel.org/all/[email protected]/#t

These codes weren't touched that frequent, it's interesting to see such
coinsidence happens. :)

> ---
>  include/migration/vmstate.h |  4 ++
>  migration/vmstate.c         | 84 +++++++++++++++++++++++--------------
>  2 files changed, 56 insertions(+), 32 deletions(-)
> 
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index 62c2abd0c49..5d7dfe70643 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -1240,8 +1240,12 @@ extern const VMStateInfo vmstate_info_qlist;
>          .flags = VMS_END, \
>      }
>  
> +int vmstate_load_field(QEMUFile *f, void *pv, size_t size,
> +                       const VMStateField *field, Error **errp);
>  int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
>                         void *opaque, int version_id, Error **errp);
> +int vmstate_save_field(QEMUFile *f, void *pv, size_t size,
> +                       const VMStateField *field, JSONWriter *vmdesc, Error 
> **errp);
>  int vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
>                         void *opaque, JSONWriter *vmdesc, Error **errp);
>  int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
> diff --git a/migration/vmstate.c b/migration/vmstate.c
> index 4d28364f7ba..8d192bcaa27 100644
> --- a/migration/vmstate.c
> +++ b/migration/vmstate.c
> @@ -131,6 +131,32 @@ static void vmstate_handle_alloc(void *ptr, const 
> VMStateField *field,
>      }
>  }
>  
> +int vmstate_load_field(QEMUFile *f, void *pv, size_t size,
> +                       const VMStateField *field, Error **errp)
> +{
> +    int ret = 0;
> +
> +    if (field->flags & VMS_STRUCT) {
> +        ret = vmstate_load_state(f, field->vmsd, pv,
> +                                 field->vmsd->version_id,
> +                                 errp);
> +    } else if (field->flags & VMS_VSTRUCT) {
> +        ret = vmstate_load_state(f, field->vmsd, pv,
> +                                 field->struct_version_id,
> +                                 errp);
> +    } else {
> +        ret = field->info->get(f, pv, size, field);
> +        if (ret < 0) {
> +            error_setg(errp,
> +                       "Failed to load element of type %s for %s: "
> +                       "%d", field->info->name,
> +                       field->name, ret);
> +        }
> +    }
> +
> +    return ret;
> +}
> +
>  int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
>                         void *opaque, int version_id, Error **errp)
>  {
> @@ -203,24 +229,7 @@ int vmstate_load_state(QEMUFile *f, const 
> VMStateDescription *vmsd,
>                      inner_field = field;
>                  }
>  
> -                if (inner_field->flags & VMS_STRUCT) {
> -                    ret = vmstate_load_state(f, inner_field->vmsd, curr_elem,
> -                                             inner_field->vmsd->version_id,
> -                                             errp);
> -                } else if (inner_field->flags & VMS_VSTRUCT) {
> -                    ret = vmstate_load_state(f, inner_field->vmsd, curr_elem,
> -                                             inner_field->struct_version_id,
> -                                             errp);
> -                } else {
> -                    ret = inner_field->info->get(f, curr_elem, size,
> -                                                 inner_field);
> -                    if (ret < 0) {
> -                        error_setg(errp,
> -                                   "Failed to load element of type %s for 
> %s: "
> -                                   "%d", inner_field->info->name,
> -                                   inner_field->name, ret);
> -                    }
> -                }
> +                ret = vmstate_load_field(f, curr_elem, size, inner_field, 
> errp);
>  
>                  /* If we used a fake temp field.. free it now */
>                  if (inner_field != field) {
> @@ -427,6 +436,29 @@ int vmstate_save_state(QEMUFile *f, const 
> VMStateDescription *vmsd,
>      return vmstate_save_state_v(f, vmsd, opaque, vmdesc_id, 
> vmsd->version_id, errp);
>  }
>  
> +int vmstate_save_field(QEMUFile *f, void *pv, size_t size,
> +                       const VMStateField *field, JSONWriter *vmdesc, Error 
> **errp)
> +{
> +    int ret = 0;
> +
> +    if (field->flags & VMS_STRUCT) {
> +        ret = vmstate_save_state(f, field->vmsd, pv, vmdesc, errp);
> +    } else if (field->flags & VMS_VSTRUCT) {
> +        ret = vmstate_save_state_v(f, field->vmsd, pv, vmdesc,
> +                                   field->struct_version_id, errp);
> +    } else {
> +        ret = field->info->put(f, pv, size, field, vmdesc);
> +        if (ret < 0) {
> +            error_setg(errp,
> +                       "Failed to save element of type %s for %s: "
> +                       "%d", field->info->name,
> +                       field->name, ret);
> +        }
> +    }
> +
> +    return ret;
> +}
> +
>  int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
>                           void *opaque, JSONWriter *vmdesc, int version_id, 
> Error **errp)
>  {
> @@ -528,19 +560,7 @@ int vmstate_save_state_v(QEMUFile *f, const 
> VMStateDescription *vmsd,
>                  vmsd_desc_field_start(vmsd, vmdesc_loop, inner_field,
>                                        i, max_elems);
>  
> -                if (inner_field->flags & VMS_STRUCT) {
> -                    ret = vmstate_save_state(f, inner_field->vmsd,
> -                                             curr_elem, vmdesc_loop, errp);
> -                } else if (inner_field->flags & VMS_VSTRUCT) {
> -                    ret = vmstate_save_state_v(f, inner_field->vmsd,
> -                                               curr_elem, vmdesc_loop,
> -                                               
> inner_field->struct_version_id,
> -                                               errp);
> -                } else {
> -                    ret = inner_field->info->put(f, curr_elem, size,
> -                                                 inner_field, vmdesc_loop);
> -                }
> -
> +                ret = vmstate_save_field(f, curr_elem, size, inner_field, 
> vmdesc_loop, errp);
>                  written_bytes = qemu_file_transferred(f) - old_offset;
>                  vmsd_desc_field_end(vmsd, vmdesc_loop, inner_field,
>                                      written_bytes);
> @@ -551,7 +571,7 @@ int vmstate_save_state_v(QEMUFile *f, const 
> VMStateDescription *vmsd,
>                  }
>  
>                  if (ret) {
> -                    error_setg(errp, "Save of field %s/%s failed",
> +                    error_prepend(errp, "Save of field %s/%s failed: ",
>                                  vmsd->name, field->name);
>                      if (vmsd->post_save) {
>                          vmsd->post_save(opaque);
> -- 
> 2.47.3
> 

-- 
Peter Xu


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