Re: [PATCH v3 04/13] net: tap: Pad short frames to minimum size before send

[Philippe Mathieu-Daudé]

On 3/16/21 9:12 AM, Bin Meng wrote:
> Do the same for tap backend as what we did for slirp.

You explained SLiRP/TAP in the previous patch. IMO these
changes could be squashed there directly (besides, same
maintainer entry).

> 
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> 
> ---
> 
> Changes in v3:
> - use the pad_short_frame() helper for tap
> 
>  net/tap-win32.c | 9 +++++++++
>  net/tap.c       | 9 +++++++++
>  2 files changed, 18 insertions(+)
> 
> diff --git a/net/tap-win32.c b/net/tap-win32.c
> index 2b5dcda36e..e044a5ca35 100644
> --- a/net/tap-win32.c
> +++ b/net/tap-win32.c
> @@ -31,6 +31,7 @@
>  
>  #include "qemu-common.h"
>  #include "clients.h"            /* net_init_tap */
> +#include "net/eth.h"
>  #include "net/net.h"
>  #include "net/tap.h"            /* tap_has_ufo, ... */
>  #include "qemu/error-report.h"
> @@ -688,9 +689,17 @@ static void tap_win32_send(void *opaque)
>      uint8_t *buf;
>      int max_size = 4096;
>      int size;
> +    uint8_t min_pkt[ETH_ZLEN];
>  
>      size = tap_win32_read(s->handle, &buf, max_size);
>      if (size > 0) {
> +        if (!s->nc.peer->do_not_pad) {
> +            if (pad_short_frame(min_pkt, buf, size)) {
> +                buf = min_pkt;
> +                size = ETH_ZLEN;
> +            }
> +        }
> +
>          qemu_send_packet(&s->nc, buf, size);
>          tap_win32_free_buffer(s->handle, buf);
>      }
> diff --git a/net/tap.c b/net/tap.c
> index b7512853f4..aa69cf1c73 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -32,6 +32,7 @@
>  #include <sys/socket.h>
>  #include <net/if.h>
>  
> +#include "net/eth.h"
>  #include "net/net.h"
>  #include "clients.h"
>  #include "monitor/monitor.h"
> @@ -189,6 +190,7 @@ static void tap_send(void *opaque)
>  
>      while (true) {
>          uint8_t *buf = s->buf;
> +        uint8_t min_pkt[ETH_ZLEN];
>  
>          size = tap_read_packet(s->fd, s->buf, sizeof(s->buf));
>          if (size <= 0) {
> @@ -200,6 +202,13 @@ static void tap_send(void *opaque)
>              size -= s->host_vnet_hdr_len;
>          }
>  
> +        if (!s->nc.peer->do_not_pad) {
> +            if (pad_short_frame(min_pkt, buf, size)) {
> +                buf = min_pkt;
> +                size = ETH_ZLEN;
> +            }
> +        }
> +
>          size = qemu_send_packet_async(&s->nc, buf, size, tap_send_completed);
>          if (size == 0) {
>              tap_read_poll(s, false);
>