Resume from Hibernation

[pbalduino]

Description

Implement the boot-time hibernation resume mechanism that detects a saved hibernate state, validates it, and restores the complete system to its pre-hibernation state.

Overview

Resume from hibernation is the counterpart to the hibernate save process. On boot, the kernel must:

• Detect if a valid hibernate image exists
• Validate the image integrity
• Restore all process state and memory
• Resume execution as if nothing happened

Boot Sequence with Hibernation

Normal Boot

1. Bootloader loads kernel
2. Kernel initializes hardware
3. Mount root filesystem
4. Launch init process
5. Start userland

Hibernation Resume Boot

1. Bootloader loads kernel with hibernate= parameter
2. Kernel initializes minimal hardware
3. Mount filesystem containing hibernate image
4. Validate hibernate image
5. Restore kernel state
6. Restore all processes and memory
7. Resume execution (skip init, userland already running)

Implementation

Detection

• Check kernel command line for hibernate parameter
• Look for hibernate image at specified path
• Validate magic number and version

Validation

• Check hibernate image magic number (HBRN)
• Verify kernel version matches
• Validate checksums/hashes
• Ensure image is complete (not truncated)

Restoration Order

1. Open hibernate file and SQLite metadata
2. Restore kernel heap (buddy allocator state)
3. Restore process structures
4. Restore memory pages (using issue 256)
5. Restore file descriptors
6. Restore signal handlers
7. Restore CPU registers for each process
8. Mark processes as runnable
9. Resume scheduler

Critical State

• TSS (Task State Segment)
• GDT (Global Descriptor Table) entries
• Page tables
• Interrupt handlers (should already be set up)
• Timer state (reset, don't restore)

Kernel Command Line

Add hibernate parameter:

API

Check if resuming from hibernation and validate image.

Failure Handling

If resume fails:

• Log error to serial/console
• Delete corrupt hibernate image
• Continue with normal boot
• Prevent infinite resume loops

Tasks

• Add hibernate parameter parsing to kernel command line
• Implement hibernate image detection
• Add image validation (magic, version, checksums)
• Implement kernel state restoration
• Restore buddy allocator arenas and freelists
• Restore process structures
• Call memory restore (issue 256)
• Restore file descriptors
• Restore signal handlers
• Restore CPU context for all processes
• Mark processes runnable and start scheduler
• Add failure handling and fallback to normal boot
• Add resume progress reporting (serial/console)
• Test with various hibernate scenarios

Integration Points

• Bootloader (Limine) command line parsing
• Process management (restore process structures)
• Memory management (restore pages and mappings)
• File system (mount and read hibernate file)
• Scheduler (resume processes)

Acceptance Criteria

• Kernel detects hibernate image on boot
• Image validation catches corruption
• All processes restored correctly
• Memory contents match pre-hibernation state
• Open files resume at correct positions
• Processes continue execution seamlessly
• Failed resume falls back to normal boot cleanly
• No memory leaks or resource leaks
• Works with multiple processes
• Shell and user programs resume successfully

Priority

High - Completes the hibernation feature

Estimated Effort

2-3 weeks

Notes

• This is the most complex piece - restoration order matters
• Must be very careful with error handling
• Consider incremental checkpoints during restore
• Extensive testing needed with edge cases