Re: [Qemu-devel] [RFC v2 3/5] vmstate: add VMS_MUST_EXIST

[Dr. David Alan Gilbert]

* Michael S. Tsirkin (address@hidden) wrote:
> Can be used to verify a required field exists or validate
> state in some other way.
> 
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  include/migration/vmstate.h |  1 +
>  vmstate.c                   | 10 +++++++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index 3a1587e..eb90cef 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -101,6 +101,7 @@ enum VMStateFlags {
>      VMS_MULTIPLY         = 0x200,  /* multiply "size" field by field_size */
>      VMS_VARRAY_UINT8     = 0x400,  /* Array with size in uint8_t field*/
>      VMS_VARRAY_UINT32    = 0x800,  /* Array with size in uint32_t field*/
> +    VMS_MUST_EXIST       = 0x1000, /* Field must exist in input */
>  };
>  
>  typedef struct {
> diff --git a/vmstate.c b/vmstate.c
> index fe53735..4943b83 100644
> --- a/vmstate.c
> +++ b/vmstate.c
> @@ -13,7 +13,7 @@ static int vmstate_n_elems(void *opaque, VMStateField 
> *field)
>  {
>      int n_elems = 1;
>  
> -    if (!(field->flags & ~VMS_NONE)) {
> +    if (!(field->flags & ~(VMS_NONE | VMS_MUST_EXIST))) {
>          n_elems = 0;
>      } else if (field->flags & VMS_ARRAY) {
>          n_elems = field->num;
> @@ -107,6 +107,9 @@ int vmstate_load_state(QEMUFile *f, const 
> VMStateDescription *vmsd,
>              }
>          }
>          field++;
> +    } else if (field->flags & VMS_MUST_EXIST) {
> +        fprintf(stderr, "Input validation failed: %s/%s\n", vmsd->name, 
> field->name);
> +        return -1;

I think your intent here is just to misuse the field_exist function pointer 
as a call for a different reason as a hook for a validator; is it really worth
misusing it like that or is something more explicit worth it?
Perhaps something passed an Error** so it could pass back what was wrong?

>      }
>      ret = vmstate_subsection_load(f, vmsd, opaque);
>      if (ret != 0) {
> @@ -148,6 +151,11 @@ void vmstate_save_state(QEMUFile *f, const 
> VMStateDescription *vmsd,
>                      field->info->put(f, addr, size);
>                  }
>              }
> +        } else {
> +            if (field->flags & VMS_MUST_EXIST) {
> +                fprintf(stderr, "Input validation failed: %s/%s\n", 
> vmsd->name, field->name);
> +                assert(!(field->flags & VMS_MUST_EXIST));

Wrong message for the save side.

Dave
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK