Add build tags for omitting network drivers and document usage

Signed-off-by: fahed dorgaa <[email protected]>

Author: fahedouch

.github/workflows/main.yaml

@@ -281,3 +281,18 @@ jobs:
         docker exec test docker info
         docker exec test ./integration-docker.sh
         docker rm -f test
+
+  build-tags:
+    name: "Build with disabled drivers tags"
+    runs-on: ubuntu-24.04
+    steps:
+    - name: "Check out"
+      uses: actions/checkout@v5
+    - name: "Set up Go"
+      uses: actions/setup-go@v5
+      with:
+        go-version-file: go.mod
+    - name: "Build with -tags no_gvisortapvsock"
+      run: go build -v -tags no_gvisortapvsock ./cmd/rootlesskit
+    - name: "Build with -tags 'no_slirp4netns no_lxcusernic no_gvisortapvsock'"
+      run: go build -v -tags "no_slirp4netns no_lxcusernic no_gvisortapvsock" ./cmd/rootlesskit

docs/BUILDING.md

@@ -0,0 +1,20 @@
+# Building RootlessKit
+
+This document describes build-time options, including Go build tags for omitting certain network and port drivers.
+
+## Build tags to omit drivers
+
+To exclude specific drivers at compilation time, use Go build tags:
+
+- Tag `no_vpnkit`: omits the VPNKit network driver implementation.
+- Tag `no_gvisortapvsock`: omits the gvisor-tap-vsock network driver implementation and its port driver.
+- Tag `no_slirp4netns`: omits the slirp4netns network driver implementation and its port driver.
+- Tag `no_lxcusernic`: omits the lxc-user-nic network driver implementation.
+
+Example:
+
+- Build without VPNKit support:
+  go build -tags no_vpnkit ./cmd/rootlesskit
+
+Notes:
+- If a disabled driver is selected at runtime (e.g., `--net=vpnkit` when built with `-tags no_vpnkit`), RootlessKit returns an error indicating that the driver was disabled at build time.