seaweedfs/test/fuse_integration/POSIX_IMPLEMENTATION_ROADMAP.md

POSIX Compliance Implementation Roadmap

This document tracks the implementation status of POSIX features in the SeaweedFS FUSE mount compliance test suite and provides a roadmap for completing comprehensive POSIX compliance testing.

Overview

The platform-specific tests listed below are implemented; this document records the implementation plan that produced them, plus the one feature still pending.

Current Status

✅ Implemented Features

• Basic file operations (create, read, write, delete)
• Directory operations (mkdir, rmdir, rename)
• File permissions and ownership
• Symbolic and hard links
• Basic I/O operations (seek, append, positioned I/O)
• File descriptors and atomic operations
• Concurrent access patterns
• Error handling compliance
• Timestamp operations

🚧 Partially Implemented

• Cross-platform compatibility (basic implementation with platform-specific access time handling)
• File sealing (still skipped; Linux-specific, pending)

✅ Implemented Platform-Specific Features

1. Extended Attributes (xattr)

Priority: High Platforms: Linux, macOS, FreeBSD

Status: Implemented

• TestExtendedAttributes/SetExtendedAttribute
• TestExtendedAttributes/ListExtendedAttributes
• TestExtendedAttributes/RemoveExtendedAttribute

Implementation Plan:

// Linux implementation
//go:build linux
func setXattr(path, name string, value []byte) error {
    return syscall.Setxattr(path, name, value, 0)
}

// macOS implementation  
//go:build darwin
func setXattr(path, name string, value []byte) error {
    return syscall.Setxattr(path, name, value, 0, 0)
}

Required Files:

• xattr_linux.go - Linux syscall implementations
• xattr_darwin.go - macOS syscall implementations
• xattr_freebsd.go - FreeBSD syscall implementations
• xattr_unsupported.go - Fallback for unsupported platforms

2. Memory Mapping (mmap)

Priority: High Platforms: All POSIX systems

Status: Implemented

• TestMemoryMapping/MemoryMappedRead
• TestMemoryMapping/MemoryMappedWrite

Implementation Plan:

func testMmap(t *testing.T, filePath string) {
    fd, err := syscall.Open(filePath, syscall.O_RDWR, 0)
    require.NoError(t, err)
    defer syscall.Close(fd)
    
    // Platform-specific mmap implementation
    data, err := syscall.Mmap(fd, 0, size, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
    require.NoError(t, err)
    defer syscall.Munmap(data)
}

Required Files:

• mmap_unix.go - Unix-like systems implementation
• mmap_windows.go - Windows implementation (if needed)

3. Vectored I/O (readv/writev)

Priority: Medium Platforms: All POSIX systems

Status: Implemented

• TestAdvancedIO/VectoredIO

Implementation Plan:

func testVectoredIO(t *testing.T, filePath string) {
    // Use syscall.Syscall for readv/writev
    // Linux: SYS_READV, SYS_WRITEV
    // Other platforms: platform-specific syscall numbers
}

4. Direct I/O

Priority: Medium
Platforms: Linux, some Unix variants

Status: Implemented

• TestDirectIO/DirectIO

Implementation Plan:

//go:build linux
func testDirectIO(t *testing.T, filePath string) {
    fd, err := syscall.Open(filePath, syscall.O_RDWR|syscall.O_DIRECT, 0)
    // Test with aligned buffers
}

5. File Preallocation (fallocate)

Priority: Medium Platforms: Linux, some Unix variants

Status: Implemented

• TestFilePreallocation/Fallocate

Implementation Plan:

//go:build linux
func testFallocate(t *testing.T, filePath string) {
    fd, err := syscall.Open(filePath, syscall.O_RDWR, 0)
    err = syscall.Syscall6(syscall.SYS_FALLOCATE, uintptr(fd), 0, 0, uintptr(size), 0, 0)
}

6. Zero-Copy Transfer (sendfile)

Priority: Low Platforms: Linux, FreeBSD, some Unix variants

Status: Implemented

• TestZeroCopyTransfer/Sendfile

Implementation Plan:

//go:build linux
func testSendfile(t *testing.T, srcPath, dstPath string) {
    // Use syscall.Syscall for sendfile
    // Platform-specific implementations
}

7. File Sealing (Linux-specific)

Priority: Low Platforms: Linux only

Current Status: File sealing test is still skipped

• TestFileSealing

Implementation Plan:

//go:build linux
func testFileSealing(t *testing.T) {
    // Use fcntl with F_ADD_SEALS, F_GET_SEALS
    // Test various seal types: F_SEAL_WRITE, F_SEAL_SHRINK, etc.
}

Implementation Strategy

Phase 1: Core Features (High Priority)

1. Extended Attributes - Essential for many applications
2. Memory Mapping - Critical for performance-sensitive applications

Phase 2: Advanced I/O (Medium Priority)

3. Vectored I/O - Important for efficient bulk operations
4. Direct I/O - Needed for database and high-performance applications
5. File Preallocation - Important for preventing fragmentation

Phase 3: Specialized Features (Low Priority)

6. Zero-Copy Transfer - Performance optimization feature
7. File Sealing - Security feature, Linux-specific

Platform Support Matrix

Feature	Linux	macOS	FreeBSD	Windows	Notes
Extended Attributes	✅	✅	✅	❌	Different syscall signatures
Memory Mapping	✅	✅	✅	✅	Standard POSIX
Vectored I/O	✅	✅	✅	❌	readv/writev syscalls
Direct I/O	✅	❌	✅	❌	O_DIRECT flag
fallocate	✅	❌	❌	❌	Linux-specific
sendfile	✅	❌	✅	❌	Platform-specific
File Sealing	✅	❌	❌	❌	Linux-only

Development Guidelines

1. Platform-Specific Implementation Pattern

// feature_linux.go
//go:build linux
package fuse
func platformSpecificFunction() { /* Linux implementation */ }

// feature_darwin.go  
//go:build darwin
package fuse
func platformSpecificFunction() { /* macOS implementation */ }

// feature_unsupported.go
//go:build !linux && !darwin
package fuse
func platformSpecificFunction() { /* Skip or error */ }

2. Test Structure Pattern

func (s *POSIXExtendedTestSuite) TestFeature(t *testing.T) {
    if !isFeatureSupported() {
        t.Skip("Feature not supported on this platform")
        return
    }
    
    t.Run("FeatureTest", func(t *testing.T) {
        // Actual test implementation
    })
}

3. Error Handling

• Use platform-specific error checking
• Provide meaningful error messages
• Gracefully handle unsupported features

Testing Strategy

1. Continuous Integration

• Run tests on multiple platforms (Linux, macOS)
• Use build tags to enable/disable platform-specific tests
• Ensure graceful degradation on unsupported platforms

2. Feature Detection

• Implement runtime feature detection where possible
• Skip tests gracefully when features are unavailable
• Log clear messages about skipped functionality

3. Documentation

• Document platform-specific behavior
• Provide examples for each implemented feature
• Maintain compatibility matrices

Contributing

When implementing these features:

1. Start with high-priority items (Extended Attributes, Memory Mapping)
2. Follow the platform-specific pattern outlined above
3. Add comprehensive tests for each feature
4. Update this roadmap as features are implemented
5. Document any platform-specific quirks or limitations

Future Enhancements

Beyond the current roadmap, consider:

• File locking (flock, fcntl locks)
• Asynchronous I/O (aio_read, aio_write)
• File change notifications (inotify, kqueue)
• POSIX ACLs (Access Control Lists)
• Sparse file operations
• File hole punching

References

• POSIX.1-2017 Standard
• Linux Programmer's Manual
• FreeBSD System Calls
• macOS System Calls