Re: [PATCH v2 5/8] net/tap: implement interfaces for local migration

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Sep 03, 2025 at 04:37:02PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Handle local-incoming option:
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> ---
>  include/net/tap.h |   4 ++
>  net/tap.c         | 136 +++++++++++++++++++++++++++++++++++++++-------
>  2 files changed, 119 insertions(+), 21 deletions(-)
> 
> diff --git a/include/net/tap.h b/include/net/tap.h
> index 6f34f13eae..3ef2e2dbae 100644
> --- a/include/net/tap.h
> +++ b/include/net/tap.h
> @@ -30,7 +30,11 @@
>  
>  int tap_enable(NetClientState *nc);
>  int tap_disable(NetClientState *nc);
> +bool tap_local_incoming(NetClientState *nc);
>  
>  int tap_get_fd(NetClientState *nc);
>  
> +int tap_load(NetClientState *nc, QEMUFile *f);
> +int tap_save(NetClientState *nc, QEMUFile *f);
> +
>  #endif /* QEMU_NET_TAP_H */
> diff --git a/net/tap.c b/net/tap.c
> index a9d955ac5f..499db756ea 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -35,6 +35,8 @@
>  #include "net/eth.h"
>  #include "net/net.h"
>  #include "clients.h"
> +#include "migration/migration.h"
> +#include "migration/qemu-file.h"
>  #include "monitor/monitor.h"
>  #include "system/system.h"
>  #include "qapi/error.h"
> @@ -82,6 +84,7 @@ typedef struct TAPState {
>      VHostNetState *vhost_net;
>      unsigned host_vnet_hdr_len;
>      Notifier exit;
> +    bool local_incoming;
>  } TAPState;
>  
>  static void launch_script(const char *setup_script, const char *ifname,
> @@ -803,6 +806,40 @@ static int net_tap_init_vhost(TAPState *s, Error **errp) {
>      return 0;
>  }
>  
> +int tap_save(NetClientState *nc, QEMUFile *f)
> +{
> +    TAPState *s = DO_UPCAST(TAPState, nc, nc);
> +
> +    qemu_file_put_fd(f, s->fd);
> +    qemu_put_byte(f, s->using_vnet_hdr);
> +    qemu_put_byte(f, s->has_ufo);
> +    qemu_put_byte(f, s->has_uso);
> +    qemu_put_byte(f, s->enabled);
> +    qemu_put_be32(f, s->host_vnet_hdr_len);


Is it neccessary to transfer that metadata, or is there perhaps a way
for the other side to query the TAP FD configuration from the kernel
to detect this ?

I'm concerned that this code / wire format is not extensible if we ever
add another similar field to TAPState in the future.

> +
> +    return 0;
> +}
> +
> +int tap_load(NetClientState *nc, QEMUFile *f)
> +{
> +    TAPState *s = DO_UPCAST(TAPState, nc, nc);
> +
> +    s->fd = qemu_file_get_fd(f);
> +    if (s->fd < 0) {
> +        return -1;
> +    }
> +
> +    s->using_vnet_hdr = qemu_get_byte(f);
> +    s->has_ufo = qemu_get_byte(f);
> +    s->has_uso = qemu_get_byte(f);
> +    s->enabled = qemu_get_byte(f);
> +    qemu_get_be32s(f, &s->host_vnet_hdr_len);
> +
> +    tap_read_poll(s, true);
> +
> +    return net_tap_init_vhost(s, NULL);
> +}
> +
>  static int net_tap_fd_init_common(const Netdev *netdev, NetClientState *peer,
>                                    const char *model, const char *name,
>                                    const char *ifname, const char *script,

With regards,
Daniel
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