Dr. David Alan Gilbert (git) <dgilb...@redhat.com> writes:
> From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
>
> VMSTATE_WITH_TMP is for handling structures where some calculation
> or rearrangement of the data needs to be performed before the data
> hits the wire.
> For example, where the value on the wire is an offset from a
> non-migrated base, but the data in the structure is the actual pointer.
>
> To use it, a temporary type is created and a vmsd used on that type.
> The first element of the type must be 'parent' a pointer back to the
> type of the main structure. VMSTATE_WITH_TMP takes care of allocating
> and freeing the temporary before running the child vmsd.
>
> The post_load/pre_save on the child vmsd can copy things from the parent
> to the temporary using the parent pointer and do any other calculations
> needed; it can then use normal VMSD entries to do the actual data
> storage without having to fiddle around with qemu_get_*/qemu_put_*
>
> Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
Reviewed-by: Alex Bennée <alex.ben...@linaro.org>
> ---
> include/migration/vmstate.h | 19 +++++++++++++++++++
> migration/vmstate.c | 40 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 59 insertions(+)
>
> diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> index cc66910..f2dfb85 100644
> --- a/include/migration/vmstate.h
> +++ b/include/migration/vmstate.h
> @@ -259,6 +259,7 @@ extern const VMStateInfo vmstate_info_cpudouble;
> extern const VMStateInfo vmstate_info_timer;
> extern const VMStateInfo vmstate_info_buffer;
> extern const VMStateInfo vmstate_info_unused_buffer;
> +extern const VMStateInfo vmstate_info_tmp;
> extern const VMStateInfo vmstate_info_bitmap;
> extern const VMStateInfo vmstate_info_qtailq;
>
> @@ -651,6 +652,24 @@ extern const VMStateInfo vmstate_info_qtailq;
> .offset = offsetof(_state, _field), \
> }
>
> +/* Allocate a temporary of type 'tmp_type', set tmp->parent to _state
> + * and execute the vmsd on the temporary. Note that we're working with
> + * the whole of _state here, not a field within it.
> + * We compile time check that:
> + * That _tmp_type contains a 'parent' member that's a pointer to the
> + * '_state' type
> + * That the pointer is right at the start of _tmp_type.
> + */
> +#define VMSTATE_WITH_TMP(_state, _tmp_type, _vmsd) { \
> + .name = "tmp", \
> + .size = sizeof(_tmp_type) + \
> + QEMU_BUILD_BUG_ON_ZERO(offsetof(_tmp_type, parent) != 0)
> + \
> + type_check_pointer(_state, \
> + typeof_field(_tmp_type, parent)), \
> + .vmsd = &(_vmsd), \
> + .info = &vmstate_info_tmp, \
> +}
> +
> #define VMSTATE_UNUSED_BUFFER(_test, _version, _size) { \
> .name = "unused", \
> .field_exists = (_test), \
> diff --git a/migration/vmstate.c b/migration/vmstate.c
> index 2b2b3a5..a3de20f 100644
> --- a/migration/vmstate.c
> +++ b/migration/vmstate.c
> @@ -935,6 +935,46 @@ const VMStateInfo vmstate_info_unused_buffer = {
> .put = put_unused_buffer,
> };
>
> +/* vmstate_info_tmp, see VMSTATE_WITH_TMP, the idea is that we allocate
> + * a temporary buffer and the pre_load/pre_save methods in the child vmsd
> + * copy stuff from the parent into the child and do calculations to fill
> + * in fields that don't really exist in the parent but need to be in the
> + * stream.
> + */
> +static int get_tmp(QEMUFile *f, void *pv, size_t size, VMStateField *field)
> +{
> + int ret;
> + const VMStateDescription *vmsd = field->vmsd;
> + int version_id = field->version_id;
> + void *tmp = g_malloc(size);
> +
> + /* Writes the parent field which is at the start of the tmp */
> + *(void **)tmp = pv;
> + ret = vmstate_load_state(f, vmsd, tmp, version_id);
> + g_free(tmp);
> + return ret;
> +}
> +
> +static int put_tmp(QEMUFile *f, void *pv, size_t size, VMStateField *field,
> + QJSON *vmdesc)
> +{
> + const VMStateDescription *vmsd = field->vmsd;
> + void *tmp = g_malloc(size);
> +
> + /* Writes the parent field which is at the start of the tmp */
> + *(void **)tmp = pv;
> + vmstate_save_state(f, vmsd, tmp, vmdesc);
> + g_free(tmp);
> +
> + return 0;
> +}
> +
> +const VMStateInfo vmstate_info_tmp = {
> + .name = "tmp",
> + .get = get_tmp,
> + .put = put_tmp,
> +};
> +
> /* bitmaps (as defined by bitmap.h). Note that size here is the size
> * of the bitmap in bits. The on-the-wire format of a bitmap is 64
> * bit words with the bits in big endian order. The in-memory format
--
Alex Bennée
