Re: [PATCH v3 06/24] migration: Add qemu_loadvm_load_state_buffer() and its handler

[Peter Xu]

On Sun, Nov 17, 2024 at 08:20:01PM +0100, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> qemu_loadvm_load_state_buffer() and its load_state_buffer
> SaveVMHandler allow providing device state buffer to explicitly
> specified device via its idstr and instance id.
> 
> Reviewed-by: Fabiano Rosas <farosas@suse.de>
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

One nitpick:

> ---
>  include/migration/register.h | 17 +++++++++++++++++
>  migration/savevm.c           | 23 +++++++++++++++++++++++
>  migration/savevm.h           |  3 +++
>  3 files changed, 43 insertions(+)
> 
> diff --git a/include/migration/register.h b/include/migration/register.h
> index ff0faf5f68c8..39991f3cc5d0 100644
> --- a/include/migration/register.h
> +++ b/include/migration/register.h
> @@ -229,6 +229,23 @@ typedef struct SaveVMHandlers {
>       */
>      int (*load_state)(QEMUFile *f, void *opaque, int version_id);
>  
> +    /* This runs outside the BQL. */
> +
> +    /**
> +     * @load_state_buffer
> +     *
> +     * Load device state buffer provided to qemu_loadvm_load_state_buffer().
> +     *
> +     * @opaque: data pointer passed to register_savevm_live()
> +     * @buf: the data buffer to load
> +     * @len: the data length in buffer
> +     * @errp: pointer to Error*, to store an error if it happens.
> +     *
> +     * Returns zero to indicate success and negative for error
> +     */
> +    int (*load_state_buffer)(void *opaque, char *buf, size_t len,
> +                             Error **errp);
> +
>      /**
>       * @load_setup
>       *
> diff --git a/migration/savevm.c b/migration/savevm.c
> index a254c38edcca..1f58a2fa54ae 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -3085,6 +3085,29 @@ int qemu_loadvm_approve_switchover(void)
>      return migrate_send_rp_switchover_ack(mis);
>  }
>  
> +int qemu_loadvm_load_state_buffer(const char *idstr, uint32_t instance_id,
> +                                  char *buf, size_t len, Error **errp)

Suggest to always return bool as success/fail, especially when using
Error**.

> +{
> +    SaveStateEntry *se;
> +
> +    se = find_se(idstr, instance_id);
> +    if (!se) {
> +        error_setg(errp,
> +                   "Unknown idstr %s or instance id %u for load state 
> buffer",
> +                   idstr, instance_id);
> +        return -1;
> +    }
> +
> +    if (!se->ops || !se->ops->load_state_buffer) {
> +        error_setg(errp,
> +                   "idstr %s / instance %u has no load state buffer 
> operation",
> +                   idstr, instance_id);
> +        return -1;
> +    }
> +
> +    return se->ops->load_state_buffer(se->opaque, buf, len, errp);
> +}
> +
>  bool save_snapshot(const char *name, bool overwrite, const char *vmstate,
>                    bool has_devices, strList *devices, Error **errp)
>  {
> diff --git a/migration/savevm.h b/migration/savevm.h
> index 4d402723bc3c..b5a4f8c8b440 100644
> --- a/migration/savevm.h
> +++ b/migration/savevm.h
> @@ -71,4 +71,7 @@ int qemu_loadvm_approve_switchover(void);
>  int qemu_savevm_state_complete_precopy_non_iterable(QEMUFile *f,
>          bool in_postcopy, bool inactivate_disks);
>  
> +int qemu_loadvm_load_state_buffer(const char *idstr, uint32_t instance_id,
> +                                  char *buf, size_t len, Error **errp);
> +
>  #endif
> 

-- 
Peter Xu