fix(linux): pass the application command to urunit in config

.github/contributors.yaml

@@ -161,3 +161,6 @@ users:
   Inuth0603:
     name: Divyam Agarwal
     email: iitdivyamagarwal@gmail.com
+  indrajithek:
+    name: Indrajith
+    email: 29561593+indrajithek@users.noreply.github.com

docs/tutorials/existing-container-linux.md

@@ -77,7 +77,7 @@ designed specifically for `urunc`. It performs the following actions:
    the container in a Kubernetes cluster, where there is a high chance that
    the gateway of the container might be in a different subnet than the IP.
    As a result, the Linux kernel will fail to set the gateway.
-2. Groups multi-word arguments correctly.
+2. Reads the application command and its arguments from the configuration.
 3. Mounts `/proc` and `/sys`.
 4. Reads and sets the environment variables for the application execution
 5. Reads and sets the uid,gid and working directory for the application execution
@@ -95,6 +95,8 @@ UCS
 UID:<uid>
 GID:<gid>
 WD:<working_dir>
+ARC:<number of arguments>
+ARV:<argument> /* one line per argument */
 UCE
 ```
 

pkg/unikontainers/unikernels/linux.go

@@ -42,6 +42,7 @@ const (
 type Linux struct {
 	App        string
 	Command    string
+	Args       []string // application command, verbatim, for urunit
 	Monitor    string
 	Env        []string
 	Net        LinuxNet
@@ -123,7 +124,11 @@ func (l *Linux) CommandString() (string, error) {
 		bootParams += " URUNIT_DEFROUTE=1"
 	}
 	if l.App != "" {
-		initParams := rdinit + "init=" + l.App + " -- " + l.Command
+		initParams := rdinit + "init=" + l.App
+		// urunit takes the application command from its configuration
+		if !l.InitrdConf {
+			initParams += " -- " + l.Command
+		}
 		bootParams += " " + initParams
 	}
 
@@ -275,6 +280,7 @@ func (l *Linux) parseCmdLine(cmdLine []string) error {
 	}
 
 	l.App = normalizedArgs[0]
+	l.Args = cmdLine[1:]
 	if len(normalizedArgs) > 1 {
 		l.Command = strings.Join(normalizedArgs[1:], " ")
 	} else {
@@ -337,6 +343,14 @@ func (l *Linux) buildUrunitConfig() string {
 	sb.WriteString("WD:")
 	sb.WriteString(l.ProcConfig.WorkDir)
 	sb.WriteString("\n")
+	sb.WriteString("ARC:")
+	sb.WriteString(strconv.Itoa(len(l.Args)))
+	sb.WriteString("\n")
+	for _, arg := range l.Args {
+		sb.WriteString("ARV:")
+		sb.WriteString(arg)
+		sb.WriteString("\n")
+	}
 	sb.WriteString(lpcEndMarker)
 	sb.WriteString("\n")
 	sb.WriteString(blkStartMarker)

pkg/unikontainers/unikernels/linux_test.go

@@ -0,0 +1,82 @@
+// Copyright (c) 2023-2026, Nubificus LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package unikernels
+
+import (
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestLinuxUrunitArgs covers the arguments that the kernel command line
+// mangles: an empty argument and a literal "--".
+func TestLinuxUrunitArgs(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name     string
+		cmdLine  []string
+		expected string
+	}{
+		{
+			name:     "empty argument",
+			cmdLine:  []string{"/urunit", "/app", "a", "", "b"},
+			expected: "ARC:4\nARV:/app\nARV:a\nARV:\nARV:b\nUCE\n",
+		},
+		{
+			name:     "literal --",
+			cmdLine:  []string{"/urunit", "/app", "a", "--", "b", "c"},
+			expected: "ARC:5\nARV:/app\nARV:a\nARV:--\nARV:b\nARV:c\nUCE\n",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			l := &Linux{InitrdConf: true, RootFsType: "virtiofs"}
+			require.NoError(t, l.parseCmdLine(tc.cmdLine))
+			assert.Contains(t, l.buildUrunitConfig(), tc.expected)
+
+			cmd, err := l.CommandString()
+			require.NoError(t, err)
+			assert.True(t, strings.HasSuffix(cmd, " init=/urunit"), "unexpected command line: %s", cmd)
+		})
+	}
+}
+
+// TestLinuxUrunitLongArgs covers an argument list longer than the kernel
+// command line (2048 bytes) with more than 32 arguments.
+func TestLinuxUrunitLongArgs(t *testing.T) {
+	t.Parallel()
+
+	cmdLine := []string{"/urunit", "/app"}
+	for i := range 40 {
+		cmdLine = append(cmdLine, strconv.Itoa(i)+strings.Repeat("x", 100))
+	}
+	l := &Linux{InitrdConf: true, RootFsType: "virtiofs"}
+	require.NoError(t, l.parseCmdLine(cmdLine))
+	conf := l.buildUrunitConfig()
+
+	assert.Contains(t, conf, "\nARC:41\n")
+	assert.Equal(t, 41, strings.Count(conf, "\nARV:"))
+	assert.Contains(t, conf, "\nARV:"+cmdLine[41]+"\nUCE\n")
+
+	cmd, err := l.CommandString()
+	require.NoError(t, err)
+	assert.True(t, strings.HasSuffix(cmd, " init=/urunit"), "unexpected command line: %s", cmd)
+}