Re: [Qemu-devel] [PATCH 6/7] xen: add net backend driver.

[Anthony Liguori <anthony@codemonkey.ws>]

Gerd Hoffmann wrote:
> This patch adds a network interface backend driver to qemu.  It is a pure
> userspace implemention using the gntdev interface.  It uses "qnet" as
> backend name in xenstore so it doesn't interfere with the netback
> backend (aka "vnif").
>
> The network backend is hooked into the corrosponding qemu vlan, i.e.
> vif 0 is hooked into vlan 0.  To make the packages actually arrive
> somewhere you additionally have to link the vlan to the outside world
> using the usual qemu command line options such as "-net tap,...".
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  Makefile.target  |    2 +-
>  hw/xen-backend.h |    1 +
>  hw/xen-machine.c |    1 +
>  hw/xen-nic.c     |  448 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 451 insertions(+), 1 deletions(-)
>  create mode 100644 hw/xen-nic.c
>
> diff --git a/Makefile.target b/Makefile.target
> index 2d599d2..281d7fa 100644
> --- a/Makefile.target
> +++ b/Makefile.target
> @@ -517,7 +517,7 @@ endif
>  
>  # xen backend driver support
>  XEN_OBJS := xen-machine.o xen-backend.o
> -XEN_OBJS += xen-console.o xen-framebuffer.o xen-disk.o
> +XEN_OBJS += xen-console.o xen-framebuffer.o xen-disk.o xen-nic.o
>  ifeq ($(CONFIG_XEN), yes)
>    OBJS += $(XEN_OBJS)
>    LIBS += $(XEN_LIBS)
> diff --git a/hw/xen-backend.h b/hw/xen-backend.h
> index 941b0a6..2db2c3c 100644
> --- a/hw/xen-backend.h
> +++ b/hw/xen-backend.h
> @@ -120,6 +120,7 @@ struct devops xen_console_ops;      /* xen_console.c     */
>  struct devops xen_kbdmouse_ops;     /* xen_framebuffer.c */
>  struct devops xen_framebuffer_ops;  /* xen_framebuffer.c */
>  struct devops xen_blkdev_ops;       /* xen_disk.c        */
> +struct devops xen_netdev_ops;       /* xen_nic.c         */
>  
>  void xen_set_display(int domid, DisplayState *ds);
>  
> diff --git a/hw/xen-machine.c b/hw/xen-machine.c
> index 1b647a2..3fa4079 100644
> --- a/hw/xen-machine.c
> +++ b/hw/xen-machine.c
> @@ -62,6 +62,7 @@ static void xenpv_init(ram_addr_t ram_size, int vga_ram_size,
>      xen_be_register("vkbd", &xen_kbdmouse_ops);
>      xen_be_register("vfb", &xen_framebuffer_ops);
>      xen_be_register("qdisk", &xen_blkdev_ops);
> +    xen_be_register("qnic", &xen_netdev_ops);
>  
>      /* setup framebuffer */
>      xen_set_display(xen_domid, ds);
> diff --git a/hw/xen-nic.c b/hw/xen-nic.c
> new file mode 100644
> index 0000000..56d1474
> --- /dev/null
> +++ b/hw/xen-nic.c
> @@ -0,0 +1,448 @@
> +/*
> + *  xen paravirt network card backend
> + *
> + *  This program is free software; you can redistribute it and/or modify
> + *  it under the terms of the GNU General Public License as published by
> + *  the Free Software Foundation; under version 2 of the License.
> + *
> + *  This program is distributed in the hope that it will be useful,
> + *  but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *  GNU General Public License for more details.
> + *
> + *  You should have received a copy of the GNU General Public License
> + *  along with this program; if not, write to the Free Software
> + *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
> + */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <stdarg.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <signal.h>
> +#include <inttypes.h>
> +#include <fcntl.h>
> +#include <errno.h>
> +#include <pthread.h>
> +#include <sys/socket.h>
> +#include <sys/ioctl.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <sys/mman.h>
> +#include <sys/wait.h>
> +#include <linux/if.h>
> +#include <linux/if_tun.h>
> +
> +#include <xs.h>
> +#include <xenctrl.h>
> +#include <xen/io/xenbus.h>
> +#include <xen/io/netif.h>
> +
> +#include "hw.h"
> +#include "net.h"
> +#include "qemu-char.h"
> +#include "xen-backend.h"
> +
> +/* ------------------------------------------------------------- */
> +
> +struct netdev {
> +    struct xendev         xendev;  /* must be first */
> +    char                  *mac;
> +    int                   tx_work;
> +    int                   tx_ring_ref;
> +    int                   rx_ring_ref;
> +    struct netif_tx_sring *txs;
> +    struct netif_rx_sring *rxs;
> +    netif_tx_back_ring_t  tx_ring;
> +    netif_rx_back_ring_t  rx_ring;
> +    VLANClientState       *vs;
> +};
> +
> +/* ------------------------------------------------------------- */
> +
> +#define PROTO_TCP  6
> +#define PROTO_UDP 17
> +
> +static uint32_t checksum_add(int len, uint8_t *buf)
> +{
> +    uint32_t sum = 0;
> +    int i;
> +
> +    for (i = 0; i < len; i++) {
> +	if (i & 1)
> +	    sum += (uint32_t)buf[i];
> +	else
> +	    sum += (uint32_t)buf[i] << 8;
> +    }
> +    return sum;
> +}
> +
> +static uint16_t checksum_finish(uint32_t sum)
> +{
> +    while (sum>>16)
> +	sum = (sum & 0xFFFF)+(sum >> 16);
> +    return ~sum;
> +}
> +
> +static uint16_t checksum_tcpudp(uint16_t length, uint16_t proto,
> +				uint8_t *addrs, uint8_t *buf)
> +{
> +    uint32_t sum = 0;
> +
> +    sum += checksum_add(length, buf);         // payload
> +    sum += checksum_add(8, addrs);            // src + dst address
> +    sum += proto + length;                    // protocol & length
> +    return checksum_finish(sum);
> +}
> +
> +static void checksum_calculate(uint8_t *data, int length)
> +{
> +    int hlen, plen, proto, csum_offset;
> +    uint16_t csum;
> +
> +    if ((data[14] & 0xf0) != 0x40)
> +	return; /* not IPv4 */
> +    hlen  = (data[14] & 0x0f) * 4;
> +    plen  = (data[16] << 8 | data[17]) - hlen;
> +    proto = data[23];
> +
> +    switch (proto) {
> +    case PROTO_TCP:
> +	csum_offset = 16;
> +	break;
> +    case PROTO_UDP:
> +	csum_offset = 6;
> +	break;
> +    default:
> +	return;
> +    }
> +
> +    if (plen < csum_offset+2)
> +	return;
> +
> +    data[14+hlen+csum_offset]   = 0;
> +    data[14+hlen+csum_offset+1] = 0;
> +    csum = checksum_tcpudp(plen, proto, data+14+12, data+14+hlen);
> +    data[14+hlen+csum_offset]   = csum >> 8;
> +    data[14+hlen+csum_offset+1] = csum & 0xff;
> +}
>
>   

The same thing is done in e1000, I believe.  We'll also probably want to 
be able to support this for virtio so this would be pretty good to make 
common code.

Regards,

Anthony Liguori