Add rootfs override (#1323)

This PR adds an option in `ContainerCreateOption` to override the root
filesystem of container. When `ContainerCreateOption.rootFsOverride` is
set, container uses that as the root fs instead of the one cloned from
image snapshot.

## Type of Change
- [ ] Bug fix
- [X] New feature  
- [ ] Breaking change
- [ ] Documentation update

## Motivation and Context
[Why is this change needed?]

## Testing
- [X] Tested locally
- [ ] Added/updated tests
- [ ] Added/updated docs

Sources/ContainerResource/Container/Bundle.swift

@@ -110,9 +110,11 @@ extension Bundle {
             try bundle.write(filename: Self.containerConfigFilename, value: containerConfiguration)
         }
 
-        if let containerRootFilesystem {
+        if let rootFsOverride = options?.rootFsOverride {
+            try bundle.setContainerRootFs(fs: rootFsOverride)
+        } else if let containerRootFilesystem {
             let readonly = containerConfiguration?.readOnly ?? false
-            try bundle.setContainerRootFs(cloning: containerRootFilesystem, readonly: readonly)
+            try bundle.cloneContainerRootFs(cloning: containerRootFilesystem, readonly: readonly)
         }
 
         if let options {
@@ -133,14 +135,18 @@ extension Bundle {
         path.appendingPathComponent(name)
     }
 
-    public func setContainerRootFs(cloning fs: Filesystem, readonly: Bool = false) throws {
+    public func setContainerRootFs(fs: Filesystem) throws {
+        let fsData = try JSONEncoder().encode(fs)
+        try fsData.write(to: self.containerRootfsConfig)
+    }
+
+    public func cloneContainerRootFs(cloning fs: Filesystem, readonly: Bool = false) throws {
         var mutableFs = fs
         if readonly && !mutableFs.options.contains("ro") {
             mutableFs.options.append("ro")
         }
         let cloned = try mutableFs.clone(to: self.containerRootfsBlock.absolutePath())
-        let fsData = try JSONEncoder().encode(cloned)
-        try fsData.write(to: self.containerRootfsConfig)
+        try setContainerRootFs(fs: cloned)
     }
 
     /// Delete the bundle and all of the resources contained inside.

Sources/ContainerResource/Container/ContainerCreateOptions.swift

@@ -15,10 +15,14 @@
 //===----------------------------------------------------------------------===//
 
 public struct ContainerCreateOptions: Codable, Sendable {
+    /// Remove the container and wipe out its data on container stop
     public let autoRemove: Bool
+    /// Override the rootFs with this one other than the image-cloned version
+    public let rootFsOverride: Filesystem?
 
-    public init(autoRemove: Bool) {
+    public init(autoRemove: Bool, rootFsOverride: Filesystem? = nil) {
         self.autoRemove = autoRemove
+        self.rootFsOverride = rootFsOverride
     }
 
     public static let `default` = ContainerCreateOptions(autoRemove: false)

Sources/Services/ContainerAPIService/Server/Containers/ContainersService.swift

@@ -364,7 +364,7 @@ public actor ContainersService {
                         "ref": "\(configuration.image.reference)",
                     ])
                 let containerImage = ClientImage(description: configuration.image)
-                let imageFs = try await containerImage.getCreateSnapshot(platform: configuration.platform)
+                let imageFs = try await options.rootFsOverride == nil ? containerImage.getCreateSnapshot(platform: configuration.platform) : nil
 
                 self.log.debug(
                     "configure runtime",