[Qemu-devel] The maximum limit of virtual network device

[Wu, Jiaxin]

Hello experts,

We know QEMU has the capability to create the multiple network devices in one 
QEMU guest with the -device syntax. But I met the below failure when I'm trying 
to create more than 30 virtual devices with the each TAP backend:

qemu-system-x86_64: -device e1000: PCI: no slot/function available for e1000, 
all in use.

The corresponding QEMU command shows as following:

sudo qemu-system-x86_64 -pflash OVMF.fd -global e1000.romfile="" -netdev 
tap,id=hostnet0,ifname=tap0,script=no,downscript=no -device 
e1000,netdev=hostnet0 -netdev 
tap,id=hostnet1,ifname=tap1,script=no,downscript=no -device 
e1000,netdev=hostnet1 -netdev 
tap,id=hostnet2,ifname=tap2,script=no,downscript=no -device 
e1000,netdev=hostnet2 -netdev 
tap,id=hostnet3,ifname=tap3,script=no,downscript=no -device 
e1000,netdev=hostnet3 -netdev 
tap,id=hostnet4,ifname=tap4,script=no,downscript=no -device 
e1000,netdev=hostnet4 -netdev 
tap,id=hostnet5,ifname=tap5,script=no,downscript=no -device 
e1000,netdev=hostnet5 -netdev 
tap,id=hostnet6,ifname=tap6,script=no,downscript=no -device 
e1000,netdev=hostnet6 -netdev 
tap,id=hostnet7,ifname=tap7,script=no,downscript=no -device 
e1000,netdev=hostnet7 -netdev 
tap,id=hostnet8,ifname=tap8,script=no,downscript=no -device 
e1000,netdev=hostnet8 -netdev 
tap,id=hostnet9,ifname=tap9,script=no,downscript=no -device 
e1000,netdev=hostnet9 -netdev 
tap,id=hostnet10,ifname=tap10,script=no,downscript=no -device 
e1000,netdev=hostnet10 -netdev 
tap,id=hostnet11,ifname=tap11,script=no,downscript=no -device 
e1000,netdev=hostnet11 -netdev 
tap,id=hostnet12,ifname=tap12,script=no,downscript=no -device 
e1000,netdev=hostnet12 -netdev 
tap,id=hostnet13,ifname=tap13,script=no,downscript=no -device 
e1000,netdev=hostnet13 -netdev 
tap,id=hostnet14,ifname=tap14,script=no,downscript=no -device 
e1000,netdev=hostnet14 -netdev 
tap,id=hostnet15,ifname=tap15,script=no,downscript=no -device 
e1000,netdev=hostnet15 -netdev 
tap,id=hostnet16,ifname=tap16,script=no,downscript=no -device 
e1000,netdev=hostnet16 -netdev 
tap,id=hostnet17,ifname=tap17,script=no,downscript=no -device 
e1000,netdev=hostnet17 -netdev 
tap,id=hostnet18,ifname=tap18,script=no,downscript=no -device 
e1000,netdev=hostnet18 -netdev 
tap,id=hostnet19,ifname=tap19,script=no,downscript=no -device 
e1000,netdev=hostnet19 -netdev 
tap,id=hostnet20,ifname=tap20,script=no,downscript=no -device 
e1000,netdev=hostnet20 -netdev 
tap,id=hostnet21,ifname=tap21,script=no,downscript=no -device 
e1000,netdev=hostnet21 -netdev 
tap,id=hostnet22,ifname=tap22,script=no,downscript=no -device 
e1000,netdev=hostnet22 -netdev 
tap,id=hostnet23,ifname=tap23,script=no,downscript=no -device 
e1000,netdev=hostnet23 -netdev 
tap,id=hostnet24,ifname=tap24,script=no,downscript=no -device 
e1000,netdev=hostnet24 -netdev 
tap,id=hostnet25,ifname=tap25,script=no,downscript=no -device 
e1000,netdev=hostnet25 -netdev 
tap,id=hostnet26,ifname=tap26,script=no,downscript=no -device 
e1000,netdev=hostnet26 -netdev 
tap,id=hostnet27,ifname=tap27,script=no,downscript=no -device 
e1000,netdev=hostnet27 -netdev 
tap,id=hostnet28,ifname=tap28,script=no,downscript=no -device 
e1000,netdev=hostnet28 -netdev 
tap,id=hostnet29,ifname=tap29,script=no,downscript=no -device 
e1000,netdev=hostnet29

>From above,  the max limit of virtual network device in one guest is about 29? 
>If not, how can I avoid such failure? My use case is to create more than 150 
>network devices in one guest. Please provide your comments on this.

Thank you!

Best Regards.
Jiaxin