tests: add bb test for symlink resolution

Verify that the last element of fs entries' paths is not followed when
resolving paths.

Test that we dont overwrite dead links when overwrite is false.

tests/negative/files/link.go

@@ -22,6 +22,7 @@ import (
 func init() {
 	register.Register(register.NegativeTest, WriteThroughRelativeSymlink())
 	register.Register(register.NegativeTest, WriteThroughAbsoluteSymlink())
+	register.Register(register.NegativeTest, WriteOverBrokenSymlink())
 }
 func WriteThroughRelativeSymlink() types.Test {
 	name := "Write Through Relative Symlink off the Root Filesystem"
@@ -114,3 +115,38 @@ func WriteThroughAbsoluteSymlink() types.Test {
 		ConfigMinVersion: configMinVersion,
 	}
 }
+
+func WriteOverBrokenSymlink() types.Test {
+	name := "Write Over Broken Symlink at end of path"
+	in := types.GetBaseDisk()
+	out := types.GetBaseDisk()
+	config := `{
+	  "ignition": { "version": "$version" },
+	  "storage": {
+	    "files": [{
+	      "filesystem": "root",
+	      "path": "/etc/file",
+	      "overwrite": false,
+	      "mode": 420
+	    }]
+	  }
+	}`
+	in[0].Partitions.AddLinks("ROOT", []types.Link{
+		{
+			Node: types.Node{
+				Name:      "file",
+				Directory: "etc",
+			},
+			Target: "/usr/rofile",
+		},
+	})
+	configMinVersion := "2.2.0"
+
+	return types.Test{
+		Name:             name,
+		In:               in,
+		Out:              out,
+		Config:           config,
+		ConfigMinVersion: configMinVersion,
+	}
+}

tests/positive/files/link.go

@@ -27,6 +27,8 @@ func init() {
 	register.Register(register.PositiveTest, WriteThroughAbsoluteSymlink())
 	register.Register(register.PositiveTest, ForceLinkCreation())
 	register.Register(register.PositiveTest, ForceHardLinkCreation())
+	register.Register(register.PositiveTest, WriteOverSymlink())
+	register.Register(register.PositiveTest, WriteOverBrokenSymlink())
 }
 
 func CreateHardLinkOnRoot() types.Test {
@@ -396,3 +398,113 @@ func ForceHardLinkCreation() types.Test {
 		ConfigMinVersion: configMinVersion,
 	}
 }
+
+func WriteOverSymlink() types.Test {
+	name := "Write Over Symlink at end of path"
+	in := types.GetBaseDisk()
+	out := types.GetBaseDisk()
+	// note this abuses the order in which ignition writes links and will break with 3.0.0
+	// Also tests that Ignition does not try to resolve symlink targets
+	config := `{
+	  "ignition": { "version": "$version" },
+	  "storage": {
+	    "files": [{
+	      "filesystem": "root",
+	      "path": "/etc/file",
+	      "mode": 420
+	    }]
+	  }
+	}`
+	in[0].Partitions.AddLinks("ROOT", []types.Link{
+		{
+			Node: types.Node{
+				Name:      "file",
+				Directory: "etc",
+			},
+			Target: "/usr/rofile",
+		},
+	})
+	in[0].Partitions.AddFiles("ROOT", []types.File{
+		{
+			Node: types.Node{
+				Name:      "rofile",
+				Directory: "usr",
+			},
+			Contents: "",
+			Mode:     420,
+		},
+	})
+	out[0].Partitions.AddFiles("ROOT", []types.File{
+		{
+			Node: types.Node{
+				Name:      "rofile",
+				Directory: "usr",
+			},
+			Contents: "",
+			Mode:     420,
+		},
+		{
+			Node: types.Node{
+				Name:      "file",
+				Directory: "etc",
+			},
+			Contents: "",
+			Mode:     420,
+		},
+	})
+	configMinVersion := "2.1.0"
+
+	return types.Test{
+		Name:             name,
+		In:               in,
+		Out:              out,
+		Config:           config,
+		ConfigMinVersion: configMinVersion,
+	}
+}
+
+func WriteOverBrokenSymlink() types.Test {
+	name := "Write Over Broken Symlink at end of path"
+	in := types.GetBaseDisk()
+	out := types.GetBaseDisk()
+	// note this abuses the order in which ignition writes links and will break with 3.0.0
+	// Also tests that Ignition does not try to resolve symlink targets
+	config := `{
+	  "ignition": { "version": "$version" },
+	  "storage": {
+	    "files": [{
+	      "filesystem": "root",
+	      "path": "/etc/file",
+	      "mode": 420
+	    }]
+	  }
+	}`
+	in[0].Partitions.AddLinks("ROOT", []types.Link{
+		{
+			Node: types.Node{
+				Name:      "file",
+				Directory: "etc",
+			},
+			Target: "/usr/rofile",
+		},
+	})
+	out[0].Partitions.AddFiles("ROOT", []types.File{
+		{
+			Node: types.Node{
+				Name:      "file",
+				Directory: "etc",
+			},
+			Contents: "",
+			Mode:     420,
+		},
+	})
+	configMinVersion := "2.1.0"
+
+	return types.Test{
+		Name:             name,
+		In:               in,
+		Out:              out,
+		Config:           config,
+		ConfigMinVersion: configMinVersion,
+	}
+}