Re: [Qemu-devel] [PATCH v6 4/4] Add support for net bridge

[Hui Kai Ran <hkran@linux.vnet.ibm.com>]

On 12/20/2011 06:02 PM, Hui Kai Ran wrote:
> On 12/19/2011 09:11 PM, Corey Bryant wrote:
>> The most common use of -net tap is to connect a tap device to a 
>> bridge.  This
>> requires the use of a script and running qemu as root in order to 
>> allocate a
>> tap device to pass to the script.
>>
>> This model is great for portability and flexibility but it's incredibly
>> difficult to eliminate the need to run qemu as root.  The only really 
>> viable
>> mechanism is to use tunctl to create a tap device, attach it to a 
>> bridge as
>> root, and then hand that tap device to qemu.  The problem with this 
>> mechanism
>> is that it requires administrator intervention whenever a user wants 
>> to create
>> a guest.
>>
>> By essentially writing a helper that implements the most common 
>> qemu-ifup
>> script that can be safely given cap_net_admin, we can dramatically 
>> simplify
>> things for non-privileged users.  We still support existing -net tap 
>> options
>> as a mechanism for advanced users and backwards compatibility.
>>
>> Currently, this is very Linux centric but there's really no reason 
>> why it
>> couldn't be extended for other Unixes.
>>
>> A typical invocation would be similar to one of the following:
>>
>>    qemu linux.img -net bridge -net nic,model=virtio
>>
>>    qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper
>>                   -net nic,model=virtio
>>
>>    qemu linux.img -netdev bridge,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>>    qemu linux.img -netdev 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> The default bridge that we attach to is br0.  The thinking is that a 
>> distro
>> could preconfigure such an interface to allow out-of-the-box bridged 
>> networking.
>>
>> Alternatively, if a user wants to use a different bridge, a typical 
>> invocation
>> would be simliar to one of the following:
>>
>>    qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
>>
>>    qemu linux.img -net 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0
>>                   -net nic,model=virtio
>>
>>    qemu linux.img -netdev bridge,br=qemubr0,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>>    qemu linux.img -netdev 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>> Signed-off-by: Richa Marwaha<rmarwah@linux.vnet.ibm.com>
>> Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>
>> ---
>>   configure       |    2 +
>>   net.c           |   29 ++++++++-
>>   net.h           |    3 +
>>   net/tap.c       |  187 
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>   net/tap.h       |    3 +
>>   qemu-options.hx |   74 ++++++++++++++++++----
>>   6 files changed, 281 insertions(+), 17 deletions(-)
>>
>> diff --git a/configure b/configure
>> index 6ed4196..4839694 100755
>> --- a/configure
>> +++ b/configure
>> @@ -2905,6 +2905,8 @@ echo "sysconfdir=$sysconfdir">>  $config_host_mak
>>   echo "docdir=$docdir">>  $config_host_mak
>>   echo "confdir=$confdir">>  $config_host_mak
>>   echo "libexecdir=\${prefix}/libexec">>  $config_host_mak
>> +echo "CONFIG_QEMU_SHAREDIR=\"$prefix$datasuffix\"">>  $config_host_mak
>> +echo "CONFIG_QEMU_HELPERDIR=\"$prefix/libexec\"">>  $config_host_mak
>>
>>   case "$cpu" in
>>     
>> i386|x86_64|alpha|arm|cris|hppa|ia64|lm32|m68k|microblaze|mips|mips64|ppc|ppc64|s390|s390x|sparc|sparc64|unicore32)
>> diff --git a/net.c b/net.c
>> index f7bebf8..9296224 100644
>> --- a/net.c
>> +++ b/net.c
>> @@ -952,6 +952,14 @@ static const struct {
>>                   .type = QEMU_OPT_STRING,
>>                   .help = "script to shut down the interface",
>>               }, {
>> +                .name = "br",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "bridge name",
>> +            }, {
>> +                .name = "helper",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "command to execute to configure bridge",
>> +            }, {
>>                   .name = "sndbuf",
>>                   .type = QEMU_OPT_SIZE,
>>                   .help = "send buffer limit"
>> @@ -1049,6 +1057,23 @@ static const struct {
>>               { /* end of list */ }
>>           },
>>       },
>> +    [NET_CLIENT_TYPE_BRIDGE] = {
>> +        .type = "bridge",
>> +        .init = net_init_bridge,
>> +        .desc = {
>> +            NET_COMMON_PARAMS_DESC,
>> +            {
>> +                .name = "br",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "bridge name",
>> +            }, {
>> +                .name = "helper",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "command to execute to configure bridge",
>> +            },
>> +            { /* end of list */ }
>> +        },
>> +    },
>>   };
>>
>>   int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
>> @@ -1071,7 +1096,8 @@ int net_client_init(Monitor *mon, QemuOpts 
>> *opts, int is_netdev)
>>   #ifdef CONFIG_VDE
>>               strcmp(type, "vde") != 0&&
>>   #endif
>> -            strcmp(type, "socket") != 0) {
>> +            strcmp(type, "socket") != 0&&
>> +            strcmp(type, "bridge") != 0) {
>>               qerror_report(QERR_INVALID_PARAMETER_VALUE, "type",
>>                             "a netdev backend type");
>>               return -1;
>> @@ -1141,6 +1167,7 @@ static int net_host_check_device(const char 
>> *device)
>>   #ifdef CONFIG_VDE
>>                                          ,"vde"
>>   #endif
>> +                                       , "bridge"
>>       };
>>       for (i = 0; i<  sizeof(valid_param_list) / sizeof(char *); i++) {
>>           if (!strncmp(valid_param_list[i], device,
>> diff --git a/net.h b/net.h
>> index c6b4190..0fd7e23 100644
>> --- a/net.h
>> +++ b/net.h
>> @@ -36,6 +36,7 @@ typedef enum {
>>       NET_CLIENT_TYPE_SOCKET,
>>       NET_CLIENT_TYPE_VDE,
>>       NET_CLIENT_TYPE_DUMP,
>> +    NET_CLIENT_TYPE_BRIDGE,
>>
>>       NET_CLIENT_TYPE_MAX
>>   } net_client_type;
>> @@ -173,6 +174,8 @@ int do_netdev_del(Monitor *mon, const QDict 
>> *qdict, QObject **ret_data);
>>
>>   #define DEFAULT_NETWORK_SCRIPT "/etc/qemu-ifup"
>>   #define DEFAULT_NETWORK_DOWN_SCRIPT "/etc/qemu-ifdown"
>> +#define DEFAULT_BRIDGE_HELPER CONFIG_QEMU_HELPERDIR 
>> "/qemu-bridge-helper"
>> +#define DEFAULT_BRIDGE_INTERFACE "br0"
>>
>>   void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
>>
>> diff --git a/net/tap.c b/net/tap.c
>> index 6c27a94..b2b82a1 100644
>> --- a/net/tap.c
>> +++ b/net/tap.c
>> @@ -382,6 +382,143 @@ static int launch_script(const char 
>> *setup_script, const char *ifname, int fd)
>>       return -1;
>>   }
>>
>> +static int recv_fd(int c)
>> +{
>> +    int fd;
>> +    uint8_t msgbuf[CMSG_SPACE(sizeof(fd))];
>> +    struct msghdr msg = {
>> +        .msg_control = msgbuf,
>> +        .msg_controllen = sizeof(msgbuf),
>> +    };
>> +    struct cmsghdr *cmsg;
>> +    struct iovec iov;
>> +    uint8_t req[1];
>> +    ssize_t len;
>> +
>> +    cmsg = CMSG_FIRSTHDR(&msg);
>> +    cmsg->cmsg_level = SOL_SOCKET;
>> +    cmsg->cmsg_type = SCM_RIGHTS;
>> +    cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
>> +    msg.msg_controllen = cmsg->cmsg_len;
>> +
>> +    iov.iov_base = req;
>> +    iov.iov_len = sizeof(req);
>> +
>> +    msg.msg_iov =&iov;
>> +    msg.msg_iovlen = 1;
>> +
>> +    len = recvmsg(c,&msg, 0);
>> +    if (len>  0) {
>> +        memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
>> +        return fd;
>> +    }
>> +
>> +    return len;
>> +}
>> +
>> +static int net_bridge_run_helper(const char *helper, const char 
>> *bridge)
>> +{
>> +    sigset_t oldmask, mask;
>> +    int pid, status;
>> +    char *args[5];
>> +    char **parg;
>> +    int sv[2];
>> +
>> +    sigemptyset(&mask);
>> +    sigaddset(&mask, SIGCHLD);
>> +    sigprocmask(SIG_BLOCK,&mask,&oldmask);
>> +
>> +    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
>> +        return -1;
>> +    }
>> +
>> +    /* try to launch bridge helper */
>> +    pid = fork();
>> +    if (pid == 0) {
>> +        int open_max = sysconf(_SC_OPEN_MAX), i;
>> +        char buf[32];
>> +
>> +        snprintf(buf, sizeof(buf), "%d", sv[1]);
>> +
>> +        for (i = 0; i<  open_max; i++) {
>> +            if (i != STDIN_FILENO&&
>> +                i != STDOUT_FILENO&&
>> +                i != STDERR_FILENO&&
>> +                i != sv[1]) {
>> +                close(i);
>> +            }
>> +        }
>> +        parg = args;
>> +        *parg++ = (char *)helper;
>> +        *parg++ = (char *)"--use-vnet";
>> +        *parg++ = (char *)bridge;
>> +        *parg++ = buf;
>> +        *parg++ = NULL;
>> +        execv(helper, args);
>> +        _exit(1);
>> +    } else if (pid>  0) {
>> +        int fd;
>> +
>> +        close(sv[1]);
>> +
>> +        do {
>> +            fd = recv_fd(sv[0]);
>> +        } while (fd == -1&&  errno == EINTR);
>> +
>> +        close(sv[0]);
>> +
>> +        while (waitpid(pid,&status, 0) != pid) {
>> +            /* loop */
>> +        }
>> +        sigprocmask(SIG_SETMASK,&oldmask, NULL);
>> +        if (fd<  0) {
>> +            fprintf(stderr, "failed to recv file descriptor\n");
>> +            return -1;
>> +        }
>> +
>> +        if (WIFEXITED(status)&&  WEXITSTATUS(status) == 0) {
>> +            return fd;
>> +        }
>> +    }
>> +    fprintf(stderr, "failed to launch bridge helper\n");
>> +    return -1;
>> +}
>> +
>> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
>> +                    VLANState *vlan)
>> +{
>> +    TAPState *s;
>> +    int fd, vnet_hdr;
>> +
>> +    if (!qemu_opt_get(opts, "br")) {
>> +        qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
>> +    }
>> +    if (!qemu_opt_get(opts, "helper")) {
>> +        qemu_opt_set(opts, "helper", DEFAULT_BRIDGE_HELPER);
>> +    }
>> +
>> +    fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
>> +                               qemu_opt_get(opts, "br"));
>> +    if (fd == -1) {
>> +        return -1;
>> +    }
>> +
>> +    fcntl(fd, F_SETFL, O_NONBLOCK);
>> +
>> +    vnet_hdr = tap_probe_vnet_hdr(fd);
>> +
>> +    s = net_tap_fd_init(vlan, "bridge", name, fd, vnet_hdr);
>> +    if (!s) {
>> +        close(fd);
>> +        return -1;
>> +    }
>> +
>> +    snprintf(s->nc.info_str, sizeof(s->nc.info_str),
>> +             "br=%s", qemu_opt_get(opts, "br"));
>> +
>> +    return 0;
>> +}
>> +
>>   static int net_tap_init(QemuOpts *opts, int *vnet_hdr)
>>   {
>>       int fd, vnet_hdr_required;
>> @@ -422,13 +559,17 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>   {
>>       TAPState *s;
>>       int fd, vnet_hdr = 0;
>> +    const char *model;
>>
>>       if (qemu_opt_get(opts, "fd")) {
>>           if (qemu_opt_get(opts, "ifname") ||
>>               qemu_opt_get(opts, "script") ||
>>               qemu_opt_get(opts, "downscript") ||
>> -            qemu_opt_get(opts, "vnet_hdr")) {
>> -            error_report("ifname=, script=, downscript= and 
>> vnet_hdr= is invalid with fd=");
>> +            qemu_opt_get(opts, "vnet_hdr") ||
>> +            qemu_opt_get(opts, "br") ||
>> +            qemu_opt_get(opts, "helper")) {
>> +            error_report("ifname=, script=, downscript=, vnet_hdr=, "
>> +                         "br= and helper= are invalid with fd=");
>>               return -1;
>>           }
>>
>> @@ -440,7 +581,41 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>           fcntl(fd, F_SETFL, O_NONBLOCK);
>>
>>           vnet_hdr = tap_probe_vnet_hdr(fd);
>> +
>> +        model = "tap";
>> +
>> +    } else if (qemu_opt_get(opts, "helper")) {
>> +        if (qemu_opt_get(opts, "ifname") ||
>> +            qemu_opt_get(opts, "script") ||
>> +            qemu_opt_get(opts, "downscript") ||
>> +            qemu_opt_get(opts, "vnet_hdr")) {
>> +            error_report("ifname=, script=, downscript=, and 
>> vnet_hdr= "
>> +                         "are invalid with helper=");
>> +            return -1;
>> +        }
>> +
>> +        if (!qemu_opt_get(opts, "br")) {
>> +            qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
>> +        }
>> +
>> +        fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
>> +                                   qemu_opt_get(opts, "br"));
>> +        if (fd == -1) {
>> +            return -1;
>> +        }
>> +
>> +        fcntl(fd, F_SETFL, O_NONBLOCK);
>> +
>> +        vnet_hdr = tap_probe_vnet_hdr(fd);
>> +
>> +        model = "bridge";
>> +
>>       } else {
>> +        if (qemu_opt_get(opts, "br")) {
>> +            error_report("br= is invalid with script=");
>> +            return -1;
>> +        }
>> +
>>           if (!qemu_opt_get(opts, "script")) {
>>               qemu_opt_set(opts, "script", DEFAULT_NETWORK_SCRIPT);
>>           }
>> @@ -453,9 +628,11 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>           if (fd == -1) {
>>               return -1;
>>           }
>> +
>> +        model = "tap";
>>       }
>>
>> -    s = net_tap_fd_init(vlan, "tap", name, fd, vnet_hdr);
>> +    s = net_tap_fd_init(vlan, model, name, fd, vnet_hdr);
>>       if (!s) {
>>           close(fd);
>>           return -1;
>> @@ -467,6 +644,10 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>
>>       if (qemu_opt_get(opts, "fd")) {
>>           snprintf(s->nc.info_str, sizeof(s->nc.info_str), "fd=%d", fd);
>> +    } else if (qemu_opt_get(opts, "helper")) {
>> +        snprintf(s->nc.info_str, sizeof(s->nc.info_str),
>> +                "helper=%s,br=%s", qemu_opt_get(opts, "helper"),
>> +                qemu_opt_get(opts, "br"));
>>       } else {
>>           const char *ifname, *script, *downscript;
>>
>> diff --git a/net/tap.h b/net/tap.h
>> index e44bd2b..56c591f 100644
>> --- a/net/tap.h
>> +++ b/net/tap.h
>> @@ -57,4 +57,7 @@ int tap_get_fd(VLANClientState *vc);
>>   struct vhost_net;
>>   struct vhost_net *tap_get_vhost_net(VLANClientState *vc);
>>
>> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
>> +                    VLANState *vlan);
>> +
>>   #endif /* QEMU_NET_TAP_H */
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index 087a3b9..4f2385d 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -1205,11 +1205,14 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>>       "-net tap[,vlan=n][,name=str],ifname=name\n"
>>       "                connect the host TAP network interface to VLAN 
>> 'n'\n"
>>   #else
>> -    "-net 
>> tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
>> -    "                connect the host TAP network interface to VLAN 
>> 'n' and use the\n"
>> -    "                network scripts 'file' (default=" 
>> DEFAULT_NETWORK_SCRIPT ")\n"
>> -    "                and 'dfile' (default=" 
>> DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
>> +    "-net 
>> tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
>> +    "                connect the host TAP network interface to VLAN 
>> 'n' \n"
>> +    "                use network scripts 'file' (default=" 
>> DEFAULT_NETWORK_SCRIPT ")\n"
>> +    "                to configure it and 'dfile' (default=" 
>> DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
>> +    "                to deconfigure it\n"
>>       "                use '[down]script=no' to disable script 
>> execution\n"
>> +    "                use network helper 'helper' (default=" 
>> DEFAULT_BRIDGE_HELPER ") and\n"
>> +    "                bridge 'br' (default=" DEFAULT_BRIDGE_INTERFACE 
>> ") to configure it\n"
>>       "                use 'fd=h' to connect to an already opened TAP 
>> interface\n"
>>       "                use 'sndbuf=nbytes' to limit the size of the 
>> send buffer (the\n"
>>       "                default is disabled 'sndbuf=0' to enable flow 
>> control set 'sndbuf=1048576')\n"
>> @@ -1219,6 +1222,10 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>>       "                    (only has effect for virtio guests which 
>> use MSIX)\n"
>>       "                use vhostforce=on to force vhost on for 
>> non-MSIX virtio guests\n"
>>       "                use 'vhostfd=h' to connect to an already 
>> opened vhost net device\n"
>> +    "-net bridge[,vlan=n][,name=str][,br=bridge][,helper=helper]\n"
>> +    "                connects a host TAP network interface to a host 
>> bridge device 'br'\n"
>> +    "                (default=" DEFAULT_BRIDGE_INTERFACE ") using 
>> the program 'helper'\n"
>> +    "                (default=" DEFAULT_BRIDGE_HELPER ")\n"
>>   #endif
>>       "-net 
>> socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
>>       "                connect the vlan 'n' to another VLAN using a 
>> socket connection\n"
>> @@ -1242,6 +1249,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>>       "user|"
>>   #endif
>>       "tap|"
>> +    "bridge|"
>>   #ifdef CONFIG_VDE
>>       "vde|"
>>   #endif
>> @@ -1378,26 +1386,66 @@ processed and applied to -net user. Mixing 
>> them with the new configuration
>>   syntax gives undefined results. Their use for new applications is 
>> discouraged
>>   as they will be removed from future versions.
>>
>> -@item -net 
>> tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}] 
>> [,script=@var{file}][,downscript=@var{dfile}]
>> -Connect the host TAP network interface @var{name} to VLAN @var{n}, use
>> -the network script @var{file} to configure it and the network script
>> +@item -net 
>> tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,br=@var{bridge}][,helper=@var{helper}]
>> +Connect the host TAP network interface @var{name} to VLAN @var{n}.
>> +
>> +Use the network script @var{file} to configure it and the network 
>> script
>>   @var{dfile} to deconfigure it. If @var{name} is not provided, the OS
>> -automatically provides one. @option{fd}=@var{h} can be used to specify
>> -the handle of an already opened host TAP interface. The default network
>> -configure script is @file{/etc/qemu-ifup} and the default network
>> -deconfigure script is @file{/etc/qemu-ifdown}. Use @option{script=no}
>> -or @option{downscript=no} to disable script execution. Example:
>> +automatically provides one. The default network configure script is
>> +@file{/etc/qemu-ifup} and the default network deconfigure script is
>> +@file{/etc/qemu-ifdown}. Use @option{script=no} or 
>> @option{downscript=no}
>> +to disable script execution.
>> +
>> +If running QEMU as an unprivileged user, use the network helper
>> +@var{helper} to configure the TAP interface. The default network
>> +helper executable is @file{/usr/local/libexec/qemu-bridge-helper}
>> +and the default bridge device is @file{br0}.
>> +
>> +@option{fd}=@var{h} can be used to specify the handle of an already
>> +opened host TAP interface.
>> +
>> +Examples:
>>
>>   @example
>> +#launch a QEMU instance with the default network script
>>   qemu linux.img -net nic -net tap
>>   @end example
>>
>> -More complicated example (two NICs, each one connected to a TAP device)
>>   @example
>> +#launch a QEMU instance with two NICs, each one connected
>> +#to a TAP device
>>   qemu linux.img -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
>>                  -net nic,vlan=1 -net tap,vlan=1,ifname=tap1
>>   @end example
>>
>> +@example
>> +#launch a QEMU instance with the default network helper to
>> +#connect a TAP device to bridge br0
>> +qemu linux.img -net nic -net 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper
>> +@end example
>> +
>> +@item -net 
>> bridge[,vlan=@var{n}][,name=@var{name}][,br=@var{bridge}][,helper=@var{helper}]
>> +Connect a host TAP network interface to a host bridge device.
>> +
>> +Use the network helper @var{helper} to configure the TAP interface and
>> +attach it to the bridge. The default network helper executable is
>> +@file{/usr/local/libexec/qemu-bridge-helper} and the default bridge
>> +device is @file{br0}.
>> +
>> +Examples:
>> +
>> +@example
>> +#launch a QEMU instance with the default network helper to
>> +#connect a TAP device to bridge br0
>> +qemu linux.img -net bridge -net nic,model=virtio
>> +@end example
>> +
>> +@example
>> +#launch a QEMU instance with the default network helper to
>> +#connect a TAP device to bridge qemubr0
>> +qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
>> +@end example
>> +
>>   @item -net socket[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}] 
>> [,listen=[@var{host}]:@var{port}][,connect=@var{host}:@var{port}]
>>
>>   Connect the VLAN @var{n} to a remote VLAN in another QEMU virtual
> Hi, I applied the patches, but an error  prompts there should be a 
> file named bridge.conf ,
> how can i find it?
>
> /home/huikai/qemu10/bin/qemu-system-x86_64 -enable-kvm -m 1024 -drive 
> file=imgs/sles.img,if=virtio -net bridge  -net nic,model=virtiofailed 
> to parse default acl file `/home/huikai/qemu10/etc/qemu/bridge.conf'
> failed to launch bridge helper
> qemu-system-x86_64: -net bridge: Device 'bridge' could not be initialize
>
>
Sorry, i found it in the patch set.