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

[Rick Vernam <rickv@hobi.com>]

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.