feat: 实现waitid系统调用及作业控制信号处理

[fslongjin]

• 新增waitid系统调用，支持WEXITED、WSTOPPED、WCONTINUED等选项
• 完善作业控制信号处理逻辑，支持SIGSTOP/SIGCONT的异步处理
• 优化信号唤醒机制，确保及时处理pending信号
• 添加waitid功能测试用例，验证系统调用正确性

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Note

Adds waitid (P_ALL/P_PID/P_PGID) with WEXITED/WSTOPPED/WCONTINUED, overhauls SIGSTOP/SIGCONT handling and signal wakeups, fixes siginfo layout, and adds comprehensive tests.

• Syscall/Wait:
  • Implement SYS_WAITID (kernel/src/process/syscall/sys_waitid.rs) with P_ALL/P_PID/P_PGID, WEXITED/WSTOPPED/WCONTINUED/WNOHANG/WNOWAIT, rusage, and siginfo_t returns.
  • Core wait logic reworked in kernel/src/process/exit.rs: race-free waits via wait queues, proper WNOWAIT reuse, WCONTINUED/WSTOPPED reporting, group (Pgid) and all (P_ALL) handling.
• Signals/Job Control:
  • Kernel-only signals (e.g., SIGKILL/SIGSTOP) handled by default path without user frames (arch/x86_64/ipc/signal.rs).
  • Job-control: async stop on STOP signals and resume on SIGCONT with SignalFlags (CLD_STOPPED/CONTINUED, STOP_*) set/cleared; parent notified via SIGCHLD; shared-pending flushes; stopped tasks not spuriously woken.
  • Refined wakeups: signal_wake_up kicks CPUs appropriately; avoid waking stopped tasks unless fatal; ProcessManager::kick avoids kicking current CPU; added ProcessManager::stop_task() and wake_all_waiters().
• Siginfo/ABI:
  • Fix siginfo_t field order (si_signo, si_errno, si_code) and add 128-byte size assert; ensure flush_by_mask also clears bitmap.
• Fork/Flags:
  • Correctly set VFORK when CLONE_VFORK in copy_flags.
• Tests:
  • Add user/apps/c_unitest/test_waitid.c covering exit, stop/continue, non-blocking, no-wait, process-group, all-children, and error cases.

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[Copilot]

Pull Request Overview

This PR implements the waitid system call functionality, a POSIX-compliant interface for waiting on child process state changes. The implementation adds comprehensive support for various wait modes including exit (WEXITED), stop (WSTOPPED), continue (WCONTINUED), non-blocking (WNOHANG), and observation-only (WNOWAIT) modes.

Key changes:

• Complete rewrite of sys_waitid to properly handle siginfo structure and rusage reporting
• Enhanced process state change tracking with SignalFlags for job control events (CLD_STOPPED, CLD_CONTINUED)
• Improved wait queue mechanism with race-free prepare-recheck-sleep pattern
• Fixed signal handling for SIGSTOP/SIGCONT to properly report to parent processes

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
user/apps/c_unitest/test_waitid.c	Comprehensive test suite covering all waitid modes and edge cases
kernel/src/process/syscall/sys_waitid.rs	Rewritten syscall handler with proper siginfo/rusage support
kernel/src/process/exit.rs	Enhanced wait logic with proper event tracking and race-free waiting
kernel/src/process/mod.rs	Added async stop_task and wake_all_waiters for job control
kernel/src/process/fork.rs	Fixed VFORK flag check from CLONE_VM to CLONE_VFORK
kernel/src/ipc/signal.rs	Enhanced SIGSTOP/SIGCONT handling with parent notification
kernel/src/ipc/signal_types.rs	Fixed PosixSigInfo field order and added size verification
kernel/src/ipc/syscall/sys_kill.rs	Added from_waitid converter for P_ALL/P_PID/P_PGID
kernel/src/ipc/generic_signal.rs	Enhanced sig_stop/sig_continue with proper flag tracking
kernel/src/arch/x86_64/ipc/signal.rs	Added kernel-only signal fast path to avoid user frame construction

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