Allow setting log level for vminitd (apple#772)

The `--log-level` option when running the agent sub-command for vminitd
was being silently ignored cause of the way the agent is being run. As a
workaround we need to read `/proc/self/cmdline` to get the right args

Author: adityaramani

Sources/Containerization/Kernel.swift

@@ -15,6 +15,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
+import Logging
 
 /// An object representing a Linux kernel used to boot a virtual machine.
 /// In addition to a path to the kernel itself, this type stores relevant
@@ -37,6 +38,11 @@ public struct Kernel: Sendable, Codable {
             self.kernelArgs.append("panic=\(level)")
         }
 
+        // Sets the log level for the Agent
+        mutating public func setAgentLogLevel(level: Logger.Level) {
+            self.initArgs.append(contentsOf: ["--log-level", level.description])
+        }
+
         /// Additional kernel arguments.
         public var kernelArgs: [String]
         /// Additional arguments passed to the Initial Process / Agent.

Tests/ContainerizationTests/KernelTests.swift

@@ -17,6 +17,7 @@
 //
 
 import Foundation
+import Logging
 import Testing
 
 @testable import Containerization
@@ -55,4 +56,38 @@ final class KernelTests {
 
         #expect(commandLine.kernelArgs == ["console=hvc0", "debug", "panic=10"])
     }
+
+    @Test func setAgentLogLevelAppendsFlagAndValue() {
+        var commandLine = Kernel.CommandLine(initArgs: [])
+        commandLine.setAgentLogLevel(level: .debug)
+        #expect(commandLine.initArgs == ["--log-level", "debug"])
+    }
+
+    @Test(arguments: [
+        (Logger.Level.trace, "trace"),
+        (.debug, "debug"),
+        (.info, "info"),
+        (.notice, "notice"),
+        (.warning, "warning"),
+        (.error, "error"),
+        (.critical, "critical"),
+    ])
+    func setAgentLogLevelForEachLevel(level: Logger.Level, expected: String) {
+        var commandLine = Kernel.CommandLine(initArgs: [])
+        commandLine.setAgentLogLevel(level: level)
+        #expect(commandLine.initArgs == ["--log-level", expected])
+    }
+
+    @Test func setAgentLogLevelPreservesExistingInitArgs() {
+        var commandLine = Kernel.CommandLine(initArgs: ["--verbose"])
+        commandLine.setAgentLogLevel(level: .info)
+        #expect(commandLine.initArgs == ["--verbose", "--log-level", "info"])
+    }
+
+    @Test func setAgentLogLevelDoesNotAffectKernelArgs() {
+        var commandLine = Kernel.CommandLine(debug: true, panic: 0, initArgs: [])
+        let kernelArgsBefore = commandLine.kernelArgs
+        commandLine.setAgentLogLevel(level: .warning)
+        #expect(commandLine.kernelArgs == kernelArgsBefore)
+    }
 }

examples/ctr-example/Package.resolved

@@ -17,7 +17,7 @@
 
 import PackageDescription
 
-let scVersion = "0.26.5"
+let scVersion = "0.33.4"
 
 let package = Package(
     name: "ctr-example",

examples/ctr-example/Package.swift

@@ -23,10 +23,14 @@ import Synchronization
 
 public struct LogLevelOption: ParsableArguments {
     @Option(name: .long, help: "Set the log level (trace, debug, info, notice, warning, error, critical)")
-    var logLevel: String = "info"
+    public var logLevel: String = "info"
 
     public init() {}
 
+    public init(logLevel: String) {
+        self.logLevel = logLevel
+    }
+
     public func resolvedLogLevel() -> Logger.Level {
         switch logLevel.lowercased() {
         case "trace":

vminitd/Sources/VminitdCore/Logging.swift

@@ -51,7 +51,9 @@ struct Application: AsyncParsableCommand {
         // so we do this synchronously before any async code runs.
         try mountProc()
 
-        var command = try parseAsRoot()
+        // When running as PID 1 with a Musl-static build, Swift's runtime
+        // captures argc/argv as empty. Recover argv from /proc/self/cmdline.
+        var command = try parseAsRoot(Self.procSelfArgv())
         if let asyncCommand = command as? AsyncParsableCommand {
             nonisolated(unsafe) var unsafeCommand = asyncCommand
             try await unsafeCommand.run()
@@ -85,6 +87,17 @@ struct Application: AsyncParsableCommand {
         try mnt.mount(createWithPerms: 0o755)
     }
 
+    // /proc/self/cmdline holds argv as NUL-separated bytes. Read it after
+    // mountProc(). Returns argv minus argv[0], suitable for parseAsRoot(_:).
+    private static func procSelfArgv() -> [String] {
+        guard let data = try? Data(contentsOf: URL(fileURLWithPath: "/proc/self/cmdline")) else {
+            return []
+        }
+        let parts = data.split(separator: 0, omittingEmptySubsequences: true)
+            .map { String(decoding: $0, as: UTF8.self) }
+        return Array(parts.dropFirst())
+    }
+
     private static func isProcMounted() -> Bool {
         guard let data = try? String(contentsOfFile: "/proc/mounts", encoding: .utf8) else {
             return false