Re: [Qemu-devel] [PATCHv2] e1000: multi-buffer packet support

[Kevin Wolf <kwolf@redhat.com>]

Am 03.02.2011 17:49, schrieb Michael S. Tsirkin:
> e1000 supports multi-buffer packets larger than rxbuf_size.
> 
> This fixes the following (on linux):
> - in guest: ifconfig eth1 mtu 16110
> - in host: ifconfig tap0 mtu 16110
>            ping -s 16082 <guest-ip>
> 
> Red Hat bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=602205
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> Changes from v1:
> 	removed dead code
> 
>  hw/e1000.c |   29 +++++++++++++++++++----------
>  1 files changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/hw/e1000.c b/hw/e1000.c
> index af101bd..3427ff3 100644
> --- a/hw/e1000.c
> +++ b/hw/e1000.c
> @@ -642,6 +642,8 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, size_t size)
>      uint16_t vlan_special = 0;
>      uint8_t vlan_status = 0, vlan_offset = 0;
>      uint8_t min_buf[MIN_BUF_SIZE];
> +    size_t desc_offset;
> +    size_t desc_size;
>  
>      if (!(s->mac_reg[RCTL] & E1000_RCTL_EN))
>          return -1;
> @@ -654,12 +656,6 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, size_t size)
>          size = sizeof(min_buf);
>      }
>  
> -    if (size > s->rxbuf_size) {
> -        DBGOUT(RX, "packet too large for buffers (%lu > %d)\n",
> -               (unsigned long)size, s->rxbuf_size);
> -        return -1;
> -    }
> -
>      if (!receive_filter(s, buf, size))
>          return size;
>  
> @@ -672,8 +668,15 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, size_t size)
>      }
>  
>      rdh_start = s->mac_reg[RDH];
> +    desc_offset = 0;
>      do {
> +        desc_size = size - desc_offset;
> +        if (desc_size > s->rxbuf_size) {
> +            desc_size = s->rxbuf_size;
> +        }
>          if (s->mac_reg[RDH] == s->mac_reg[RDT] && s->check_rxov) {
> +            /* Discard all data written so far */
> +            s->mac_reg[RDH] = rdh_start;
>              set_ics(s, 0, E1000_ICS_RXO);
>              return -1;
>          }
> @@ -684,9 +687,15 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, size_t size)
>          desc.status |= (vlan_status | E1000_RXD_STAT_DD);
>          if (desc.buffer_addr) {
>              cpu_physical_memory_write(le64_to_cpu(desc.buffer_addr),
> -                                      (void *)(buf + vlan_offset), size);
> -            desc.length = cpu_to_le16(size + fcs_len(s));
> -            desc.status |= E1000_RXD_STAT_EOP|E1000_RXD_STAT_IXSM;
> +                                      (void *)(buf + desc_offset + vlan_offset),
> +                                      desc_size);
> +            desc_offset += desc_size;
> +            if (desc_offset >= size) {
> +                desc.length = cpu_to_le16(desc_size + fcs_len(s));

I think this is not quite right: What happens if desc_size + fcs_len(s)
> s->rxbuf_size? IIUC, we would seemingly overflow the guests buffer (in
reality we leave the extra bytes untouched, but we may confuse the guest).

Kevin