Implement shared container support to reduce storage waste

[Meloon33]

Problem

GameNative currently creates a separate isolated container per game, duplicating the full Wine/Proton prefix (~2.9 GB) for each title. This results in severe storage waste, especially problematic on devices with limited internal storage.

Example: 5 games = ~14.5 GB of redundant container data on internal storage, even when games themselves are installed on external storage.

Current Architecture

imagefs/home/xuser-STEAM_123456/    ~2.9 GB (Game 1 container)
imagefs/home/xuser-STEAM_654321/    ~2.9 GB (Game 2 container)
imagefs/home/xuser-EPIC_987654/     ~2.9 GB (Game 3 container)

All containers forced to internal storage (/data/data/app.gamenative/), regardless of game location.

---

Proposed Solution

Implement optional shared container support alongside existing per-game containers:

1. Shared Container Mode

• One Wine/Proton prefix shared by multiple games
• Per-game launch configs (environment variables, DXVK settings, drive mappings)
• Per-game registry isolation (optional, via game-specific prefix copies on-demand)
• Storage savings: ~2.9 GB base + per-game overrides (~500 MB) instead of ~2.9 GB per game

2. External Storage Support

• Allow containers to reside on external OTG/SD cards
• No fallback to internal storage for shared prefix data
• Per-game saves/configs cached locally (minimal)
• Use symlink/bind mount pattern where supported

3. Backward Compatibility

• Keep existing per-game containers as default
• New "Shared Container" feature as opt-in per game library
• Existing per-game containers continue to work unchanged

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Implementation Outline

Phase 1: Storage Location Configuration

• Add UI to select container storage location (internal / external volume)
• Implement path resolution for external volumes (OTG, SD card)
• Ensure proper permission handling (scoped storage on Android 11+)

Phase 2: Shared Container Creation

• Extend ContainerUtils.kt to support container sharing mode
• Modify ContainerStorageManager.kt to track container references (1:N games)
• Implement container lifecycle (first game creates, last game deletes)

Phase 3: Per-Game Launch Isolation

• Drive mapping per game (currently per-container)
• Environment variable overrides per game
• Game-specific registry hive or copy-on-write mechanism
• Steam AppID mapping for Goldberg/native Steam launches

Phase 4: External Storage I/O

• Handle slow I/O from external storage (prefetch, cache strategies)
• Fallback to internal temp storage for performance-critical files
• Monitor space and warn on low disk

Phase 5: Migration Tools (Optional, Later)

• Batch convert per-game containers to shared mode
• Container consolidation UI
• Per-game data extraction if reverting to isolated mode

---

Data Model Changes

ContainerStorageManager.kt

data class ContainerConfig(
    val containerId: String,           // "STEAM_123456"
    val storageMode: StorageMode,      // ISOLATED or SHARED
    val sharedContainerId: String?,    // Reference to parent if shared
    val storageLocation: StorageLocation, // INTERNAL or EXTERNAL
    val externalPath: String?,         // Path on OTG/SD if external
)

enum class StorageMode {
    ISOLATED,    // Current: per-game prefix
    SHARED,      // New: shared prefix, per-game overrides
}

enum class StorageLocation {
    INTERNAL,
    EXTERNAL,
}

ContainerUtils.kt

// New functions
fun createSharedContainer(context: Context, storageLocation: StorageLocation): Container
fun addGameToSharedContainer(context: Context, gameAppId: String, sharedContainerId: String): Boolean
fun removeGameFromSharedContainer(context: Context, gameAppId: String): Boolean
fun getSharedContainerGames(context: Context, sharedContainerId: String): List<String>
fun getContainerStorageLocation(context: Context, containerId: String): StorageLocation

---

Storage Impact (Example with 5 Games)

Current (Per-Game Containers)

Internal Storage:  14.5 GB (5 × 2.9 GB containers)
External Storage:  150 GB (game installs)
Total Used:        164.5 GB

Proposed (Shared Container Mode)

Internal Storage:  ~3.5 GB (1 × 2.9 GB base + 0.6 GB per-game overrides)
External Storage:  150 GB (game installs)
Total Used:        153.5 GB
Savings:           11 GB (6.7% reduction)

Savings scale with number of games: 10 games = ~25 GB saved, 20 games = ~52 GB saved

---

Risks & Mitigations

Risk	Mitigation
Game interference (shared registry)	Optional per-game hive or CoW prefix
Slow external I/O blocking launch	Async load, local cache layer
Permission/access issues on external storage	Validate paths, graceful fallback to internal
User confusion (which mode to use?)	Clear UI labeling, recommended defaults, docs

---

Related Issues / Discussion

• Reference: Shared container for multiple games + optional external storage support #1624
• Original reporter: @Meloon33

Success Criteria

• Shared container holds 3+ games without conflicts
• Storage usage per additional game ≤ 500 MB (excluding game install)
• External storage games launch without internal fallback
• No regression in per-game container performance
• UI clearly indicates storage mode and location per game

[nahnotnathan]

This is a very thorough write up that nearly perfectly captures my feedback. Thanks for the effort. While I'm sure the devs are well aware of this issue, I think this outline is actually very helpful and the phases suggested are reasonable.

I would add as a note: The space savings are FAR MORE significant when you look at less demanding indie games, most of which clock in at under 1.5GB per game installed. The 2.9GB container overhead is enormous for these games. Which is a bummer because less demanding indie games are where Windows emulation really shines.

Would love to use Steam versions instead of native Android ports to enable cross save and achievements, but it honestly doesn't make a ton of sense when the container overhead is this large.

Hoping this gets implemented before EOY.