On a Thursday in 2020, Daniel P. Berrangé wrote:
This flag was added by Linux with:
commit f43798c27684ab925adde7d8acc34c78c6e50df8
Author: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
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.
Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx>
---
src/util/virnetdevtap.c | 63 +----------------------------------------
1 file changed, 1 insertion(+), 62 deletions(-)
diff --git a/src/util/virnetdevtap.c b/src/util/virnetdevtap.c
index cbce5c71b7..77c4d1c52c 100644
--- a/src/util/virnetdevtap.c
+++ b/src/util/virnetdevtap.c
@@ -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
The TUNSETIFF guard above (which was introduced in Linux eons ago) seems to be enough according to our CI: https://gitlab.com/janotomko/libvirt/-/pipelines/193942161 It builds even with the IFF_MULTI_QUEUE guard removed. commit bbb009941efaece3898910a862f6d23aa55d6ba8 CommitDate: 2012-11-01 11:14:08 -0400 tuntap: introduce multiqueue flags But #ifdef removal is out of scope of this patch. Reviewed-by: Ján Tomko <jtomko@xxxxxxxxxx> Jano
- 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
--
2.26.2
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