Re: [PATCH v5 25/36] vfio/migration: Multifd device state transfer support - receive init/cleanup

["Cédric Le Goater" <clg@redhat.com>]

On 2/19/25 21:34, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
> 
> Add support for VFIOMultifd data structure that will contain most of the
> receive-side data together with its init/cleanup methods.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
>   hw/vfio/migration-multifd.c   | 33 +++++++++++++++++++++++++++++++++
>   hw/vfio/migration-multifd.h   |  8 ++++++++
>   hw/vfio/migration.c           | 29 +++++++++++++++++++++++++++--
>   include/hw/vfio/vfio-common.h |  3 +++
>   4 files changed, 71 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c
> index 7328ad8e925c..c2defc0efef0 100644
> --- a/hw/vfio/migration-multifd.c
> +++ b/hw/vfio/migration-multifd.c
> @@ -41,6 +41,9 @@ typedef struct VFIOStateBuffer {
>       size_t len;
>   } VFIOStateBuffer;
>   
> +typedef struct VFIOMultifd {
> +} VFIOMultifd;
> +
>   static void vfio_state_buffer_clear(gpointer data)
>   {
>       VFIOStateBuffer *lb = data;
> @@ -84,8 +87,38 @@ static VFIOStateBuffer *vfio_state_buffers_at(VFIOStateBuffers *bufs, guint idx)
>       return &g_array_index(bufs->array, VFIOStateBuffer, idx);
>   }
>   
> +VFIOMultifd *vfio_multifd_new(void)
> +{
> +    VFIOMultifd *multifd = g_new(VFIOMultifd, 1);
> +
> +    return multifd;
> +}
> +
> +void vfio_multifd_free(VFIOMultifd *multifd)
> +{
> +    g_free(multifd);
> +}
> +
>   bool vfio_multifd_transfer_supported(void)
>   {
>       return multifd_device_state_supported() &&
>           migrate_send_switchover_start();
>   }
> +
> +bool vfio_multifd_transfer_enabled(VFIODevice *vbasedev)
> +{
> +    return false;
> +}
> +
> +bool vfio_multifd_transfer_setup(VFIODevice *vbasedev, Error **errp)
> +{
> +    if (vfio_multifd_transfer_enabled(vbasedev) &&
> +        !vfio_multifd_transfer_supported()) {
> +        error_setg(errp,
> +                   "%s: Multifd device transfer requested but unsupported in the current config",
> +                   vbasedev->name);
> +        return false;
> +    }
> +
> +    return true;
> +}
> diff --git a/hw/vfio/migration-multifd.h b/hw/vfio/migration-multifd.h
> index 8fe004c1da81..1eefba3b2eed 100644
> --- a/hw/vfio/migration-multifd.h
> +++ b/hw/vfio/migration-multifd.h
> @@ -12,6 +12,14 @@
>   
>   #include "hw/vfio/vfio-common.h"
>   
> +typedef struct VFIOMultifd VFIOMultifd;
> +
> +VFIOMultifd *vfio_multifd_new(void);
> +void vfio_multifd_free(VFIOMultifd *multifd);
> +
>   bool vfio_multifd_transfer_supported(void);
> +bool vfio_multifd_transfer_enabled(VFIODevice *vbasedev);
> +
> +bool vfio_multifd_transfer_setup(VFIODevice *vbasedev, Error **errp);
>   
>   #endif
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 7b79be6ad293..4311de763885 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -674,15 +674,40 @@ static void vfio_save_state(QEMUFile *f, void *opaque)
>   static int vfio_load_setup(QEMUFile *f, void *opaque, Error **errp)
>   {
>       VFIODevice *vbasedev = opaque;
> +    VFIOMigration *migration = vbasedev->migration;
> +    int ret;
> +
> +    if (!vfio_multifd_transfer_setup(vbasedev, errp)) {
> +        return -EINVAL;
> +    }
> +
> +    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
> +                                   migration->device_state, errp);
> +    if (ret) {
> +        return ret;
> +    }
>   
> -    return vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
> -                                    vbasedev->migration->device_state, errp);
> +    if (vfio_multifd_transfer_enabled(vbasedev)) {
> +        assert(!migration->multifd);
> +        migration->multifd = vfio_multifd_new();

When called from vfio_load_setup(), I think vfio_multifd_transfer_setup()
should allocate migration->multifd at the same time. It would simplify
the setup to one step. Maybe we could add a bool parameter ? because,
IIRC, you didn't like the idea of allocating it always, that is in
vfio_save_setup() too.

For symmetry, could vfio_save_cleanup() call vfio_multifd_cleanup() too ?
a setup implies a cleanup.

Thanks,

C.


> +    }
> +
> +    return 0;
> +}
> +
> +static void vfio_multifd_cleanup(VFIODevice *vbasedev)
> +{
> +    VFIOMigration *migration = vbasedev->migration;
> +
> +    g_clear_pointer(&migration->multifd, vfio_multifd_free);
>   }
>   
>   static int vfio_load_cleanup(void *opaque)
>   {
>       VFIODevice *vbasedev = opaque;
>   
> +    vfio_multifd_cleanup(vbasedev);
> +
>       vfio_migration_cleanup(vbasedev);
>       trace_vfio_load_cleanup(vbasedev->name);
>   
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 64ee3b1a2547..ab110198bd6b 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -78,6 +78,8 @@ typedef struct VFIORegion {
>       uint8_t nr; /* cache the region number for debug */
>   } VFIORegion;
>   
> +typedef struct VFIOMultifd VFIOMultifd;
> +
>   typedef struct VFIOMigration {
>       struct VFIODevice *vbasedev;
>       VMChangeStateEntry *vm_state;
> @@ -89,6 +91,7 @@ typedef struct VFIOMigration {
>       uint64_t mig_flags;
>       uint64_t precopy_init_size;
>       uint64_t precopy_dirty_size;
> +    VFIOMultifd *multifd;
>       bool initial_data_sent;
>   
>       bool event_save_iterate_started;
>