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util: stop probing for IFF_VNET_HDR

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This flag was added by Linux with:

  commit f43798c27684ab925adde7d8acc34c78c6e50df8
  Author: Rusty Russell <rusty@rustcorp.com.au>
  Date:   Thu Jul 3 03:48:02 2008 -0700

    tun: Allow GSO using virtio_net_hdr

so we can assume all Linux distros we support have this flag available
and thus the compile time check is sufficient.

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
This commit is contained in:
Daniel P. Berrangé 2020-09-24 10:27:03 +01:00
parent fcdc387410
commit 5e6d02e0f2
1 changed files with 1 additions and 62 deletions
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63
src/util/virnetdevtap.c
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@ -183,66 +183,6 @@ virNetDevTapGetRealDeviceName(char *ifname G_GNUC_UNUSED)
}
/**
* virNetDevProbeVnetHdr:
* @tapfd: a tun/tap file descriptor
*
* Check whether it is safe to enable the IFF_VNET_HDR flag on the
* tap interface.
*
* Setting IFF_VNET_HDR enables QEMU's virtio_net driver to allow
* guests to pass larger (GSO) packets, with partial checksums, to
* the host. This greatly increases the achievable throughput.
*
* It is only useful to enable this when we're setting up a virtio
* interface. And it is only *safe* to enable it when we know for
* sure that a) qemu has support for IFF_VNET_HDR and b) the running
* kernel implements the TUNGETIFF ioctl(), which qemu needs to query
* the supplied tapfd.
*
* Returns 1 if VnetHdr is supported, 0 if not supported
*/
#ifdef IFF_VNET_HDR
static int
virNetDevProbeVnetHdr(int tapfd)
{
# if defined(IFF_VNET_HDR) && defined(TUNGETFEATURES) && defined(TUNGETIFF)
unsigned int features;
struct ifreq dummy;
if (ioctl(tapfd, TUNGETFEATURES, &features) != 0) {
VIR_INFO("Not enabling IFF_VNET_HDR; "
"TUNGETFEATURES ioctl() not implemented");
return 0;
}
if (!(features & IFF_VNET_HDR)) {
VIR_INFO("Not enabling IFF_VNET_HDR; "
"TUNGETFEATURES ioctl() reports no IFF_VNET_HDR");
return 0;
}
/* The kernel will always return -1 at this point.
* If TUNGETIFF is not implemented then errno == EBADFD.
*/
if (ioctl(tapfd, TUNGETIFF, &dummy) != -1 || errno != EBADFD) {
VIR_INFO("Not enabling IFF_VNET_HDR; "
"TUNGETIFF ioctl() not implemented");
return 0;
}
VIR_INFO("Enabling IFF_VNET_HDR");
return 1;
# else
(void) tapfd;
VIR_INFO("Not enabling IFF_VNET_HDR; disabled at build time");
return 0;
# endif
}
#endif
#ifdef TUNSETIFF
/**
* virNetDevTapGenerateName:
@ -363,8 +303,7 @@ int virNetDevTapCreate(char **ifname,
}
# ifdef IFF_VNET_HDR
if ((flags & VIR_NETDEV_TAP_CREATE_VNET_HDR) &&
virNetDevProbeVnetHdr(fd))
if (flags & VIR_NETDEV_TAP_CREATE_VNET_HDR)
ifr.ifr_flags |= IFF_VNET_HDR;
# endif