[Qemu-devel] multiple tun/tap instances no longer working

[Qemu-devel] multiple tun/tap instances no longer working

[Rick Vernam]

I recently built cvs, and found that I can no longer have multiple instances 
of qemu using tun/tap.

the invocation of qemu includes, for each instance:
-net nic -net tap,script=/etc/qemu-ifup

/etc/qemu-ifup:
#!/bin/sh
sudo /sbin/ifconfig $1 192.168.2.196
sudo brctl addif br0 $1

strace of qemu-system-x86_64:
...
open("/dev/net/tun", O_RDWR)            = 3
ioctl(3, TUNSETIFF, 0x7fffca661bf0)     = -1 EBUSY (Device or resource busy)
write(2, "warning: could not configure /de"..., 72warning: could not 
configure /dev/net/tun: no virtual network emulation
) = 72
close(3)                                = 0
write(2, "Could not initialize device \'tap"..., 34Could not initialize 
device 'tap'
) = 34
exit_group(1)                           = ?
Process 8206 detached


The only thing that has changed is building qemu from cvs yesterday.  Prior to 
that, I had been using cvs from a few weeks ago.

I'm not too familiar with qemu source, but I will start looking at some of the 
commits from the past few weeks for anything.

Any ideas?
Thanks.

Re: [Qemu-devel] multiple tun/tap instances no longer working

[Rick Vernam]

in vl.c, it looks like tap_open is called with an uninitialized ifname - 
instead of ifname[0] == '\0', or a valid ifname, it is a bunch of gibberish - 
in my 
case, "ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ"

I'm not all that great with gdbg yet, so it might take me a while to figure 
out where the bad call to tap_open is coming from...

On Tuesday 09 January 2007 10:57, Rick Vernam wrote:
> I recently built cvs, and found that I can no longer have multiple
> instances of qemu using tun/tap.
>
> the invocation of qemu includes, for each instance:
> -net nic -net tap,script=/etc/qemu-ifup
>
> /etc/qemu-ifup:
> #!/bin/sh
> sudo /sbin/ifconfig $1 192.168.2.196
> sudo brctl addif br0 $1
>
> strace of qemu-system-x86_64:
> ...
> open("/dev/net/tun", O_RDWR)            = 3
> ioctl(3, TUNSETIFF, 0x7fffca661bf0)     = -1 EBUSY (Device or resource
> busy) write(2, "warning: could not configure /de"..., 72warning: could not
> configure /dev/net/tun: no virtual network emulation
> ) = 72
> close(3)                                = 0
> write(2, "Could not initialize device \'tap"..., 34Could not initialize
> device 'tap'
> ) = 34
> exit_group(1)                           = ?
> Process 8206 detached
>
>
> The only thing that has changed is building qemu from cvs yesterday.  Prior
> to that, I had been using cvs from a few weeks ago.
>
> I'm not too familiar with qemu source, but I will start looking at some of
> the commits from the past few weeks for anything.
>
> Any ideas?
> Thanks.
>
>
> _______________________________________________
> Qemu-devel mailing list
> Qemu-devel@nongnu.org
> http://lists.nongnu.org/mailman/listinfo/qemu-devel

Re: [Qemu-devel] multiple tun/tap instances no longer working

[Rick Vernam]

[-- Attachment #1: Type: text/plain, Size: 2165 bytes --]

I'm not too familiar with diff, so if the attached patch is no good, please do 
let me know how to correct it.


On Tuesday 09 January 2007 11:57, Rick Vernam wrote:
> in vl.c, it looks like tap_open is called with an uninitialized ifname -
> instead of ifname[0] == '\0', or a valid ifname, it is a bunch of gibberish
> - in my
> case,
> "ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ"
>
> I'm not all that great with gdbg yet, so it might take me a while to figure
> out where the bad call to tap_open is coming from...
>
> On Tuesday 09 January 2007 10:57, Rick Vernam wrote:
> > I recently built cvs, and found that I can no longer have multiple
> > instances of qemu using tun/tap.
> >
> > the invocation of qemu includes, for each instance:
> > -net nic -net tap,script=/etc/qemu-ifup
> >
> > /etc/qemu-ifup:
> > #!/bin/sh
> > sudo /sbin/ifconfig $1 192.168.2.196
> > sudo brctl addif br0 $1
> >
> > strace of qemu-system-x86_64:
> > ...
> > open("/dev/net/tun", O_RDWR)            = 3
> > ioctl(3, TUNSETIFF, 0x7fffca661bf0)     = -1 EBUSY (Device or resource
> > busy) write(2, "warning: could not configure /de"..., 72warning: could
> > not configure /dev/net/tun: no virtual network emulation
> > ) = 72
> > close(3)                                = 0
> > write(2, "Could not initialize device \'tap"..., 34Could not initialize
> > device 'tap'
> > ) = 34
> > exit_group(1)                           = ?
> > Process 8206 detached
> >
> >
> > The only thing that has changed is building qemu from cvs yesterday. 
> > Prior to that, I had been using cvs from a few weeks ago.
> >
> > I'm not too familiar with qemu source, but I will start looking at some
> > of the commits from the past few weeks for anything.
> >
> > Any ideas?
> > Thanks.
> >
> >
> > _______________________________________________
> > Qemu-devel mailing list
> > Qemu-devel@nongnu.org
> > http://lists.nongnu.org/mailman/listinfo/qemu-devel
>
> _______________________________________________
> Qemu-devel mailing list
> Qemu-devel@nongnu.org
> http://lists.nongnu.org/mailman/listinfo/qemu-devel

[-- Attachment #2: vl.c.patch --]
[-- Type: text/x-diff, Size: 673 bytes --]

--- qemu/vl.c	2007-01-07 16:04:40.000000000 -0600
+++ vl.c	2007-01-09 12:16:09.000000000 -0600
@@ -3885,9 +3885,11 @@
             ret = -1;
             if (net_tap_fd_init(vlan, fd))
                 ret = 0;
         } else {
-            get_param_value(ifname, sizeof(ifname), "ifname", p);
+            if (get_param_value(ifname, sizeof(ifname), "ifname", p) == 0) {
+               ifname[0]='\0';
+            }
             if (get_param_value(setup_script, sizeof(setup_script), "script", p) == 0) {
                 pstrcpy(setup_script, sizeof(setup_script), DEFAULT_NETWORK_SCRIPT);
             }
             ret = net_tap_init(vlan, ifname, setup_script);