Re: [Qemu-devel] [PATCH 00/19 v2] Add virtio-net/tap support for partial csums and GSO

[Juha.Riihimaki]

On Oct 22, 2009, at 19:43, ext Mark McLoughlin wrote:

> Hey,
>        Over a year ago we added some code to qemu-kvm.git which takes
> advantage of the recent tun/tap IFF_VNET_HDR feature in order to allow
> virtio-net to send and receive packets with partial checksums and
> segmentation offloaded:
>
>  http://article.gmane.org/gmane.comp.emulators.kvm.devel/20440
>
>  "This allows us to pass larger packets and packets with
>  partial checkums between the guest and the host, greatly
>  increasing the achievable bandwidth."
>
>        Unfortunately, that implementation was quite hacky as it
> made some assumptions that would break if e.g. you added another
> network client to a vlan where the feature had enabled.
>
>        Now that we have the -netdev parameter, we can more safely
> pair the NIC and backend, allowing us to negatiate features like
> this.
>
>        What follows is a somewhat cleaned up version of the code
> from qemu-kvm.git. Further cleanups are probably possible, but I
> think this much is mergeable. Some points of discussion:

I think this patch set has broken the QEMU build on OS X. The reason  
is that there are some definitions in tap-linux.h which only gets  
included in net.c if __linux__ is defined but the other parts of net.c  
which utilize definitions from tap-linux.h get compiled in  
nevertheless. It compiles if all definitions (except for the extra  
includes) from tap-linux.h are included for OS X as well. I've  
attached below a sample of the compiler output.


Regards,
Juha

---
[...]
   CC    net.o
net.c: In function ‘tap_receive_iov’:
net.c:1391: error: variable ‘hdr’ has initializer but incomplete type
net.c:1391: warning: excess elements in struct initializer
net.c:1391: warning: (near initialization for ‘hdr’)
net.c:1391: error: storage size of ‘hdr’ isn’t known
net.c:1391: warning: unused variable ‘hdr’
net.c: In function ‘tap_receive_raw’:
net.c:1409: error: variable ‘hdr’ has initializer but incomplete type
net.c:1409: warning: excess elements in struct initializer
net.c:1409: warning: (near initialization for ‘hdr’)
net.c:1409: error: storage size of ‘hdr’ isn’t known
net.c:1409: warning: unused variable ‘hdr’
net.c: In function ‘tap_send’:
net.c:1484: error: invalid application of ‘sizeof’ to incomplete type  
‘struct virtio_net_hdr’
net.c:1485: error: invalid application of ‘sizeof’ to incomplete type  
‘struct virtio_net_hdr’
net.c: In function ‘tap_set_sndbuf’:
net.c:1511: error: ‘TUNSETSNDBUF’ undeclared (first use in this  
function)
net.c:1511: error: (Each undeclared identifier is reported only once
net.c:1511: error: for each function it appears in.)
net.c: In function ‘tap_probe_vnet_hdr’:
net.c:1552: error: ‘TUNGETIFF’ undeclared (first use in this function)
net.c:1557: error: ‘IFF_VNET_HDR’ undeclared (first use in this  
function)
net.c: In function ‘tap_set_offload’:
net.c:1567: error: ‘TUN_F_CSUM’ undeclared (first use in this function)
net.c:1569: error: ‘TUN_F_TSO4’ undeclared (first use in this function)
net.c:1571: error: ‘TUN_F_TSO6’ undeclared (first use in this function)
net.c:1573: error: ‘TUN_F_TSO_ECN’ undeclared (first use in this  
function)
net.c:1575: error: ‘TUN_F_UFO’ undeclared (first use in this function)
net.c:1578: error: ‘TUNSETOFFLOAD’ undeclared (first use in this  
function)
net.c: In function ‘net_tap_fd_init’:
net.c:1623: error: ‘TUN_F_CSUM’ undeclared (first use in this function)
net.c:1623: error: ‘TUN_F_UFO’ undeclared (first use in this function)
net.c:1624: error: ‘TUNSETOFFLOAD’ undeclared (first use in this  
function)
make[1]: *** [net.o] Error 1
make: *** [build-all] Error 2