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| FreeBSD 5内核源代码分析之系统调用过程 |
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处理Traced系统调用。
| 代码: |
/* * Handle reschedule and other end-of-syscall issues */ userret(td, &frame, sticks); |
做一些调度处理等，后面另分析。
| 代码: |
#ifdef KTRACE if (KTRPOINT(td, KTR_SYSRET)) ktrsysret(code, error, td->td_retval[0]); #endif /* * This works because errno is findable through the * register set. If we ever support an emulation where this * is not the case, this code will need to be revisited. */ STOPEVENT(p, S_SCX, code); PTRACESTOP_SC(p, td, S_PT_SCX); #ifdef DIAGNOSTIC cred_free_thread(td); #endif WITNESS_WARN(WARN_PANIC, NULL, "System call %s returning", (code >= 0 && code < SYS_MAXSYSCALL) ? syscallnames[_code] : "???"); mtx_assert(&sched_lock, MA_NOTOWNED); mtx_assert(&Giant, MA_NOTOWNED); } |
4, userret()函数
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简要地看一下userret()函数。
| 代码: |
/* * Define the code needed before returning to user mode, for * trap and syscall. * * MPSAFE */ void userret(td, frame, oticks) struct thread *td; struct trapframe *frame; u_int oticks; { struct proc *p = td->td_proc; CTR3(KTR_SYSC, "userret: thread %p (pid %d, %s)", td, p->p_pid, p->p_comm); #ifdef INVARIANTS /* Check that we called signotify() enough. */ PROC_LOCK(p); mtx_lock_spin(&sched_lock); if (SIGPENDING(td) && ((td->td_flags & TDF_NEEDSIGCHK) == 0 || (td->td_flags & TDF_ASTPENDING) == 0)) printf("failed to set signal flags properly for ast()\n"); mtx_unlock_spin(&sched_lock); PROC_UNLOCK(p); #endif /* * Let the scheduler adjust our priority etc. */ sched_userret(td); |
调度器处理。
| 代码: |
/* * We need to check to see if we have to exit or wait due to a * single threading requirement or some other STOP condition. * Don't bother doing all the work if the stop bits are not set * at this time.. If we miss it, we miss it.. no big deal. */ if (P_SHOULDSTOP(p)) { PROC_LOCK(p); thread_suspend_check(0); /* Can suspend or kill */ PROC_UNLOCK(p); } |
是否需要停住？系统的某些时候只允许单个线程运行。
| 代码: |
/* * Do special thread processing, e.g. upcall tweaking and such. */ if (p->p_flag & P_SA) { thread_userret(td, frame); } |
又是scheduler activation的东西，通知用户态的thread manager。
(FIXME)
| 代码: |
/* * Charge system time if profiling. */ if (p->p_flag & P_PROFIL) { quad_t ticks; mtx_lock_spin(&sched_lock); ticks = td->td_sticks - oticks; mtx_unlock_spin(&sched_lock); addupc_task(td, TRAPF_PC(frame), (u_int)ticks * psratio); } } |
最后是profiling的东西。