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stuff

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This commit is contained in:
JackDoan
2026-04-20 11:57:48 -05:00
parent f34e8fe0e6
commit f4907b6634
3 changed files with 27 additions and 33 deletions
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27
overlay/tun_linux.go
View File

@@ -47,7 +47,7 @@ type tunFile struct {
segOff int // cursor into segBuf for the current ReadBatch drain
pending [][]byte // segments waiting to be drained by Read
pendingIdx int
writeIovs [2]unix.Iovec // preallocated iovecs for Write (coalescer passthrough); iovs[0] is fixed to zeroVnetHdr
writeIovs [2]unix.Iovec // preallocated iovecs for Write (coalescer passthrough); iovs[0] is fixed to validVnetHdr
// rejectIovs is a second preallocated iovec scratch used exclusively by
// WriteReject (reject + self-forward from the inside path). It mirrors
// writeIovs but lets listenIn goroutines emit reject packets without
@@ -55,7 +55,7 @@ type tunFile struct {
rejectIovs [2]unix.Iovec
// gsoHdrBuf is a per-queue 10-byte scratch for the virtio_net_hdr emitted
// by WriteGSO. Separate from zeroVnetHdr so a concurrent non-GSO Write on
// by WriteGSO. Separate from validVnetHdr so a concurrent non-GSO Write on
// another queue never observes a half-written header.
gsoHdrBuf [virtioNetHdrLen]byte
// gsoIovs is the writev iovec scratch for WriteGSO. Sized to hold the
@@ -69,10 +69,15 @@ type tunFile struct {
// any reallocations.
const gsoInitialPayIovs = 66
// zeroVnetHdr is the 10-byte virtio_net_hdr we prepend to every TUN write when
// IFF_VNET_HDR is active. All-zero signals "no GSO, no checksum offload"; the
// kernel accepts the packet as-is.
var zeroVnetHdr [virtioNetHdrLen]byte
// validVnetHdr is the 10-byte virtio_net_hdr we prepend to every non-GSO TUN
// write. Only flag set is VIRTIO_NET_HDR_F_DATA_VALID, which marks the skb
// CHECKSUM_UNNECESSARY so the receiving network stack skips L4 checksum
// verification. All packets that reach the plain Write / WriteReject paths
// already carry a valid L4 checksum (either supplied by a remote peer whose
// ciphertext we AEAD-authenticated, or produced by finishChecksum during TSO
// segmentation, or built locally by CreateRejectPacket), so trusting them is
// safe.
var validVnetHdr = [virtioNetHdrLen]byte{unix.VIRTIO_NET_HDR_F_DATA_VALID}
// newFriend makes a tunFile for a MultiQueueReader that copies the shutdown eventfd from the parent tun
func (r *tunFile) newFriend(fd int) (*tunFile, error) {
@@ -95,9 +100,9 @@ func (r *tunFile) newFriend(fd int) (*tunFile, error) {
}
if r.vnetHdr {
out.segBuf = make([]byte, tunSegBufCap)
out.writeIovs[0].Base = &zeroVnetHdr[0]
out.writeIovs[0].Base = &validVnetHdr[0]
out.writeIovs[0].SetLen(virtioNetHdrLen)
out.rejectIovs[0].Base = &zeroVnetHdr[0]
out.rejectIovs[0].Base = &validVnetHdr[0]
out.rejectIovs[0].SetLen(virtioNetHdrLen)
out.gsoIovs = make([]unix.Iovec, 2, 2+gsoInitialPayIovs)
out.gsoIovs[0].Base = &out.gsoHdrBuf[0]
@@ -133,9 +138,9 @@ func newTunFd(fd int, vnetHdr bool) (*tunFile, error) {
}
if vnetHdr {
out.segBuf = make([]byte, tunSegBufCap)
out.writeIovs[0].Base = &zeroVnetHdr[0]
out.writeIovs[0].Base = &validVnetHdr[0]
out.writeIovs[0].SetLen(virtioNetHdrLen)
out.rejectIovs[0].Base = &zeroVnetHdr[0]
out.rejectIovs[0].Base = &validVnetHdr[0]
out.rejectIovs[0].SetLen(virtioNetHdrLen)
out.gsoIovs = make([]unix.Iovec, 2, 2+gsoInitialPayIovs)
out.gsoIovs[0].Base = &out.gsoHdrBuf[0]
@@ -340,7 +345,7 @@ func (r *tunFile) writeWithScratch(buf []byte, iovs *[2]unix.Iovec) (int, error)
return 0, nil
}
// Point the payload iovec at the caller's buffer. iovs[0] is pre-wired
// to zeroVnetHdr during tunFile construction so we don't rebuild it here.
// to validVnetHdr during tunFile construction so we don't rebuild it here.
iovs[1].Base = &buf[0]
iovs[1].SetLen(len(buf))
iovPtr := uintptr(unsafe.Pointer(&iovs[0]))

2
overlay/tun_linux_offload_test.go
View File

@@ -313,7 +313,7 @@ func TestTunFileWriteVnetHdrNoAlloc(t *testing.T) {
t.Cleanup(func() { _ = unix.Close(fd) })
tf := &tunFile{fd: fd, vnetHdr: true}
tf.writeIovs[0].Base = &zeroVnetHdr[0]
tf.writeIovs[0].Base = &validVnetHdr[0]
tf.writeIovs[0].SetLen(virtioNetHdrLen)
payload := make([]byte, 1400)