feat: 가상화 문서들 추가

2026-09-10 08:54:05 +09:00
parent e9f6a93327
commit 43e1aadef0
695 changed files with 153404 additions and 12754 deletions
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+# control/setup path 는 QEMU 를 지나고 data path 는 backend 에 따라 QEMU 를 지나기도 안 지나기도 한다
+
+## Alternative text
+
+위쪽 줄은 virsh, libvirt, QEMU, virtio-net Device Model 로 이어지는 control/setup path 이고 아래쪽 줄은 Physical NIC 에서 TAP 까지 이어지는 data path 다. 두 줄이 vhost-net 과 QEMU virtio backend 에서 만나 virtqueue 를 지나 Guest 로 모이는 구성도.
+
+## Long description
+
+왼쪽에서 오른쪽으로 읽는다. 위쪽 줄이 control/setup path 다. virsh 에서 libvirt 와 QEMU 를 지나 virtio-net Device Model 에 닿고, 그 device model 이 virtual NIC 생성과 feature negotiation, virtqueue 설정, vhost-net backend 설정을 맡는다. 아래쪽 줄이 data path 다. Physical NIC 에서 Physical NIC Driver 와 Linux Bridge, TAP 까지 온다. 두 줄은 네 번째 열 다음에서 만난다. device model 은 점선으로 backend 둘을 설정하고, TAP 은 실선으로 그 둘 가운데 실제로 쓰는 쪽에 packet 을 넘긴다. vhost-net 을 쓰면 packet 은 Host Kernel 안에서 처리돼 QEMU 사용자 공간을 지나지 않고, QEMU virtio backend 를 쓰면 같은 packet 이 QEMU 사용자 공간을 지난다. 어느 쪽이든 virtqueue 에서 만나 Guest 로 올라간다. 이 Host 가 둘 중 어느 backend 를 쓰고 있는지는 그림이 말하지 않는다.
+
+## Elements and evidence
+
+- **virsh** (cli): VM/network 관리 CLI. packet datapath 에는 직접 참여하지 않는다. Evidence: L5662–L5662, L5687–L5689.
+- **libvirt** (service): VM lifecycle 과 NIC/network configuration 을 관리한다. Evidence: L5663–L5663, L5691–L5691.
+- **QEMU** (process): 실제로 실행되는 프로세스. 이 안에 virtio-net device model 이 있다. Evidence: L5666–L5666, L5693–L5693.
+- **virtio-net Device Model** (service): control/setup path 가 닿는 자리. 장치를 만들고 backend 를 연결한다. Evidence: L5666–L5666, L5695–L5700.
+- **Physical NIC** (hardware): 밖에서 온 packet 이 처음 닿는 하드웨어. Evidence: L5706–L5708.
+- **Physical NIC Driver** (driver): 그 하드웨어를 제어하는 Host kernel driver. Evidence: L5674–L5674, L5710–L5710.
+- **Linux Bridge /
+Routing / NAT** (network): L2 software switch 와 L3 routing, 주소 변환이 놓이는 자리. Evidence: L5672–L5673, L5712–L5712.
+- **TAP** (network): VM 의 Ethernet frame 과 Host Linux networking 을 잇는 접점. Evidence: L5671–L5671, L5714–L5714.
+- **vhost-net** (kernel): 반복되는 packet datapath 를 Host kernel 에서 처리하는 backend. Evidence: L5669–L5669, L5716–L5716.
+- **QEMU virtio backend** (process): vhost-net 을 쓰지 않을 때 datapath backend 를 맡는 쪽. Evidence: L5668–L5668, L5742–L5742.
+- **virtqueue** (queue): Guest 와 Host backend 가 I/O buffer 를 주고받는 descriptor 기반 공유 큐. Evidence: L5667–L5667, L5718–L5718.
+- **Guest** (service): packet 이 올라가 애플리케이션 socket 에 닿는 쪽. Evidence: L5664–L5665, L5720–L5726.
+
+## Relationships
+
+- **Linux Bridge /
+Routing / NAT → TAP:** Ethernet Frame. Evidence: L5671–L5671, L5712–L5714.
+- **Physical NIC Driver → Linux Bridge /
+Routing / NAT:** L2 forwarding. Evidence: L5672–L5672, L5710–L5712.
+- **libvirt → QEMU:** NIC/network configuration. Evidence: L5663–L5663, L5691–L5693.
+- **Physical NIC → Physical NIC Driver:** Ethernet Frame. Evidence: L5671–L5671, L5708–L5710.
+- **QEMU virtio backend → virtqueue:** Data Path. Evidence: L5729–L5729, L5742–L5744.
+- **QEMU → virtio-net Device Model:** QEMU process. Evidence: L5666–L5666, L5693–L5695.
+- **virtio-net Device Model → QEMU virtio backend:** control. Evidence: L5668–L5668, L5700–L5700.
+- **virtio-net Device Model → vhost-net:** vhost-net backend 설정. Evidence: L5700–L5700, L5716–L5716.
+- **TAP → QEMU virtio backend:** data. Evidence: L5729–L5729, L5740–L5742.
+- **TAP → vhost-net:** vhost-net 사용. Evidence: L5703–L5703, L5714–L5716.
+- **vhost-net → virtqueue:** Data Path. Evidence: L5703–L5703, L5716–L5718.
+- **virsh → libvirt:** Control / Setup. Evidence: L5662–L5663, L5684–L5691.
+- **virtqueue → Guest:** virtio-net Frontend Driver. Evidence: L5664–L5664, L5718–L5726.
@@ -0,0 +1,52 @@
+# control/setup path 는 QEMU 를 지나고 data path 는 backend 에 따라 QEMU 를 지나기도 안 지나기도 한다
+# Question: 설정하는 경로와 packet 이 흐르는 경로는 어디에서 갈라지고, 그 두 갈래 가운데 어느 쪽이 QEMU 사용자 공간을 지나는가
+direction: down
+n0: "virsh" {
+  shape: rectangle
+}
+n1: "libvirt" {
+  shape: rectangle
+}
+n2: "QEMU" {
+  shape: rectangle
+}
+n3: "virtio-net Device Model" {
+  shape: rectangle
+}
+n4: "Physical NIC" {
+  shape: rectangle
+}
+n5: "Physical NIC Driver" {
+  shape: rectangle
+}
+n6: "Linux Bridge /\nRouting / NAT" {
+  shape: rectangle
+}
+n7: "TAP" {
+  shape: rectangle
+}
+n8: "vhost-net" {
+  shape: rectangle
+}
+n9: "QEMU virtio backend" {
+  shape: rectangle
+}
+n10: "virtqueue" {
+  shape: queue
+}
+n11: "Guest" {
+  shape: rectangle
+}
+n0 -> n1: "Control / Setup"
+n1 -> n2: "NIC/network configuration"
+n2 -> n3: "QEMU process"
+n4 -> n5: "Ethernet Frame"
+n5 -> n6: "L2 forwarding"
+n6 -> n7: "Ethernet Frame"
+n3 -> n8: "vhost-net backend 설정"
+n3 -> n9
+n7 -> n8: "vhost-net 사용"
+n7 -> n9
+n8 -> n10: "Data Path"
+n9 -> n10: "Data Path"
+n10 -> n11: "virtio-net Frontend Driver"
@@ -0,0 +1,113 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<mxfile host="app.diagrams.net" modified="2026-07-23T00:00:00.000Z" agent="techviz-harness" version="24.7.17" type="device">
+  <diagram id="packet-control-and-data-paths" name="control/setup path 는 QEMU 를 지나고 data path 는 backend 에 따라 QEMU 를 지나기도 안 지나기도 한다">
+    <mxGraphModel dx="680" dy="1296" grid="1" gridSize="10" guides="1" tooltips="1" connect="1" arrows="1" fold="1" page="1" pageScale="1" pageWidth="827" pageHeight="1296" math="0" shadow="0">
+      <root>
+        <mxCell id="0"/>
+        <mxCell id="1" parent="0"/>
+        <mxCell id="n_virsh" value="virsh&lt;br/&gt;User" tooltip="VM/network 관리 CLI. packet datapath 에는 직접 참여하지 않는다. | Evidence: L5662-L5662, L5687-L5689" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="90.5" y="60.0" width="150.0" height="71.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_physical-nic" value="Physical NIC" tooltip="밖에서 온 packet 이 처음 닿는 하드웨어. | Evidence: L5706-L5708" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="300.5" y="63.5" width="150.0" height="64.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_libvirt" value="libvirt" tooltip="VM lifecycle 과 NIC/network configuration 을 관리한다. | Evidence: L5663-L5663, L5691-L5691" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="82.0" y="227.0" width="150.0" height="64.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_physical-nic-driver" value="Physical NIC Driver" tooltip="그 하드웨어를 제어하는 Host kernel driver. | Evidence: L5674-L5674, L5710-L5710" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="292.0" y="227.0" width="167.0" height="64.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_qemu" value="QEMU&lt;br/&gt;Host Userspace" tooltip="실제로 실행되는 프로세스. 이 안에 virtio-net device model 이 있다. | Evidence: L5666-L5666, L5693-L5693" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="90.5" y="388.5" width="150.0" height="71.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_linux-bridge" value="Linux Bridge /
+Routing / NAT" tooltip="L2 software switch 와 L3 routing, 주소 변환이 놓이는 자리. | Evidence: L5672-L5673, L5712-L5712" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="300.5" y="387.0" width="150.0" height="74.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_virtio-net-device-model" value="virtio-net Device Model&lt;br/&gt;virtual NIC 생성&lt;br/&gt;feature negotiation&lt;br/&gt;virtqueue 설정&lt;br/&gt;vhost-net backend 설정" tooltip="control/setup path 가 닿는 자리. 장치를 만들고 backend 를 연결한다. | Evidence: L5666-L5666, L5695-L5700" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;strokeColor=#2563eb;strokeWidth=2;" vertex="1" parent="1">
+          <mxGeometry x="70.0" y="557.0" width="174.0" height="142.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_tap" value="TAP&lt;br/&gt;Host-side interface" tooltip="VM 의 Ethernet frame 과 Host Linux networking 을 잇는 접점. | Evidence: L5671-L5671, L5714-L5714" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="304.0" y="592.5" width="167.0" height="71.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_qemu-virtio-backend" value="QEMU virtio backend&lt;br/&gt;QEMU Userspace" tooltip="vhost-net 을 쓰지 않을 때 datapath backend 를 맡는 쪽. | Evidence: L5668-L5668, L5742-L5742" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="82.0" y="795.0" width="167.0" height="71.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_vhost-net" value="vhost-net&lt;br/&gt;Host Kernel" tooltip="반복되는 packet datapath 를 Host kernel 에서 처리하는 backend. | Evidence: L5669-L5669, L5716-L5716" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="309.0" y="795.0" width="150.0" height="71.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_virtqueue" value="virtqueue&lt;br/&gt;shared queue" tooltip="Guest 와 Host backend 가 I/O buffer 를 주고받는 descriptor 기반 공유 큐. | Evidence: L5667-L5667, L5718-L5718" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="195.5" y="962.0" width="150.0" height="71.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="n_guest" value="Guest&lt;br/&gt;virtio-net Frontend Driver&lt;br/&gt;Guest TCP/IP Stack&lt;br/&gt;Socket&lt;br/&gt;Keycloak" tooltip="packet 이 올라가 애플리케이션 socket 에 닿는 쪽. | Evidence: L5664-L5665, L5720-L5726" style="whiteSpace=wrap;html=1;rounded=1;strokeWidth=2;fontSize=14;fontStyle=1;fillColor=#ffffff;strokeColor=#2d4357;verticalAlign=middle;" vertex="1" parent="1">
+          <mxGeometry x="162.5" y="1129.0" width="216.0" height="122.0" as="geometry"/>
+        </mxCell>
+        <mxCell id="e_bridge-to-tap" value="Ethernet Frame" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_linux-bridge" target="n_tap">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="381.5" y="498.8" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_driver-to-bridge" value="L2 forwarding" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_physical-nic-driver" target="n_linux-bridge">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="399.5" y="339.0" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_libvirt-to-qemu" value="NIC/network configuration" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_libvirt" target="n_qemu">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="161.2" y="311.8" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_nic-to-driver" value="Ethernet Frame" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_physical-nic" target="n_physical-nic-driver">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="399.5" y="177.2" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_qemu-backend-to-virtqueue" value="Data Path" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_qemu-virtio-backend" target="n_virtqueue">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="213.5" y="886.0" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_qemu-to-device-model" value="QEMU process" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_qemu" target="n_virtio-net-device-model">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="161.2" y="480.2" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_setup-qemu-backend" value="" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_virtio-net-device-model" target="n_qemu-virtio-backend">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="152.2" y="719.0" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_setup-vhost-backend" value="vhost-net backend 설정" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_virtio-net-device-model" target="n_vhost-net">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="270.5" y="719.0" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_tap-to-qemu-backend" value="" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_tap" target="n_qemu-virtio-backend">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="276.5" y="701.2" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_tap-to-vhost" value="vhost-net 사용" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_tap" target="n_vhost-net">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="394.8" y="701.2" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_vhost-to-virtqueue" value="Data Path" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_vhost-net" target="n_virtqueue">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="331.8" y="886.0" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_virsh-to-libvirt" value="Control / Setup" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_virsh" target="n_libvirt">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="161.2" y="151.0" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+        <mxCell id="e_virtqueue-to-guest" value="virtio-net Frontend Driver" style="edgeStyle=orthogonalEdgeStyle;rounded=0;orthogonalLoop=1;jettySize=auto;html=1;strokeWidth=2;endArrow=block;endFill=1;" edge="1" parent="1" source="n_virtqueue" target="n_guest">
+          <mxGeometry relative="1" as="geometry">
+            <mxPoint x="294.5" y="1081.0" as="offset"/>
+          </mxGeometry>
+        </mxCell>
+      </root>
+    </mxGraphModel>
+  </diagram>
+</mxfile>
@@ -0,0 +1,31 @@
+{
+  "harness_version": "0.2.0",
+  "spec_id": "packet-control-and-data-paths",
+  "spec_version": "1.1",
+  "spec_sha256": "fa2d5e22352fa6cf975665cd431a236deaa4ae88ea0eb8461bb1b3c8b0b03dc6",
+  "source_context": {
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+    "document_sha256": "181e2b3cc8a45bae81e7e8193d026937c4d586ae4495d3b2c323eb7e6abcfadd",
+    "anchor": {
+      "kind": "heading",
+      "value": "125. 최종 기준 구조",
+      "line": 5682
+    }
+  },
+  "outputs": [
+    "packet-control-and-data-paths.svg",
+    "packet-control-and-data-paths.drawio",
+    "packet-control-and-data-paths.mmd",
+    "packet-control-and-data-paths.d2",
+    "packet-control-and-data-paths.excalidraw",
+    "packet-control-and-data-paths.alt.md"
+  ],
+  "lint_issue_count": 4,
+  "assumption_count": 0,
+  "assumptions_allowed": false,
+  "composition_profile": "component-flow",
+  "reference_ids": [
+    "payment-event-flow"
+  ],
+  "diagram_only": true
+}
@@ -0,0 +1,28 @@
+%% control/setup path 는 QEMU 를 지나고 data path 는 backend 에 따라 QEMU 를 지나기도 안 지나기도 한다
+%% question: 설정하는 경로와 packet 이 흐르는 경로는 어디에서 갈라지고, 그 두 갈래 가운데 어느 쪽이 QEMU 사용자 공간을 지나는가
+flowchart TB
+    n0["virsh"]
+    n1["libvirt"]
+    n2["QEMU"]
+    n3["virtio-net Device Model"]
+    n4["Physical NIC"]
+    n5["Physical NIC Driver"]
+    n6["Linux Bridge /<br/>Routing / NAT"]
+    n7["TAP"]
+    n8["vhost-net"]
+    n9["QEMU virtio backend"]
+    n10(["virtqueue"])
+    n11["Guest"]
+    n0 -->|"Control / Setup"| n1
+    n1 -->|"NIC/network configuration"| n2
+    n2 -->|"QEMU process"| n3
+    n4 -->|"Ethernet Frame"| n5
+    n5 -->|"L2 forwarding"| n6
+    n6 -->|"Ethernet Frame"| n7
+    n3 -->|"vhost-net backend 설정"| n8
+    n3 --> n9
+    n7 -->|"vhost-net 사용"| n8
+    n7 --> n9
+    n8 -->|"Data Path"| n10
+    n9 -->|"Data Path"| n10
+    n10 -->|"virtio-net Frontend Driver"| n11
@@ -0,0 +1,160 @@
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+<title id="diagram-title">control/setup path 는 QEMU 를 지나고 data path 는 backend 에 따라 QEMU 를 지나기도 안 지나기도 한다</title>
+<desc id="diagram-description">왼쪽에서 오른쪽으로 읽는다. 위쪽 줄이 control/setup path 다. virsh 에서 libvirt 와 QEMU 를 지나 virtio-net Device Model 에 닿고, 그 device model 이 virtual NIC 생성과 feature negotiation, virtqueue 설정, vhost-net backend 설정을 맡는다. 아래쪽 줄이 data path 다. Physical NIC 에서 Physical NIC Driver 와 Linux Bridge, TAP 까지 온다. 두 줄은 네 번째 열 다음에서 만난다. device model 은 점선으로 backend 둘을 설정하고, TAP 은 실선으로 그 둘 가운데 실제로 쓰는 쪽에 packet 을 넘긴다. vhost-net 을 쓰면 packet 은 Host Kernel 안에서 처리돼 QEMU 사용자 공간을 지나지 않고, QEMU virtio backend 를 쓰면 같은 packet 이 QEMU 사용자 공간을 지난다. 어느 쪽이든 virtqueue 에서 만나 Guest 로 올라간다. 이 Host 가 둘 중 어느 backend 를 쓰고 있는지는 그림이 말하지 않는다.</desc>
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