/*
   * JFFS2 -- Journalling Flash File System, Version 2.
   *
   * Copyright © 2001-2007 Red Hat, Inc.
   * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
   *
   * Created by David Woodhouse <dwmw2@infradead.org>
   *
   * For licensing information, see the file 'LICENCE' in this directory.
   *
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/kernel.h>
  #include <linux/jffs2.h>
  #include <linux/mtd/mtd.h>
  #include <linux/completion.h>
  #include <linux/sched.h>
  #include <linux/freezer.h>
  #include <linux/kthread.h>
  #include "nodelist.h"
  
  
  static int jffs2_garbage_collect_thread(void *);
  
  void jffs2_garbage_collect_trigger(struct jffs2_sb_info *c)
  {
  	assert_spin_locked(&c->erase_completion_lock);
  	if (c->gc_task && jffs2_thread_should_wake(c))
  		send_sig(SIGHUP, c->gc_task, 1);
  }
  
  /* This must only ever be called when no GC thread is currently running */
  int jffs2_start_garbage_collect_thread(struct jffs2_sb_info *c)
  {
  	struct task_struct *tsk;
  	int ret = 0;
  
  	BUG_ON(c->gc_task);
  
  	init_completion(&c->gc_thread_start);
  	init_completion(&c->gc_thread_exit);
  
  	tsk = kthread_run(jffs2_garbage_collect_thread, c, "jffs2_gcd_mtd%d", c->mtd->index);
  	if (IS_ERR(tsk)) {
  		pr_warn("fork failed for JFFS2 garbage collect thread: %ld
  ",
  			-PTR_ERR(tsk));
  		complete(&c->gc_thread_exit);
  		ret = PTR_ERR(tsk);
  	} else {
  		/* Wait for it... */
  		jffs2_dbg(1, "Garbage collect thread is pid %d
  ", tsk->pid);
  		wait_for_completion(&c->gc_thread_start);
  		ret = tsk->pid;
  	}
  
  	return ret;
  }
  
  void jffs2_stop_garbage_collect_thread(struct jffs2_sb_info *c)
  {
  	int wait = 0;
  	spin_lock(&c->erase_completion_lock);
  	if (c->gc_task) {
  		jffs2_dbg(1, "Killing GC task %d
  ", c->gc_task->pid);
  		send_sig(SIGKILL, c->gc_task, 1);
  		wait = 1;
  	}
  	spin_unlock(&c->erase_completion_lock);
  	if (wait)
  		wait_for_completion(&c->gc_thread_exit);
  }
  
  static int jffs2_garbage_collect_thread(void *_c)
  {
  	struct jffs2_sb_info *c = _c;
  
  	allow_signal(SIGKILL);
  	allow_signal(SIGSTOP);
  	allow_signal(SIGCONT);
  
  	c->gc_task = current;
  	complete(&c->gc_thread_start);
  
  	set_user_nice(current, 10);
  
  	set_freezable();
  	for (;;) {
  		allow_signal(SIGHUP);
  	again:
  		spin_lock(&c->erase_completion_lock);
  		if (!jffs2_thread_should_wake(c)) {
  			set_current_state (TASK_INTERRUPTIBLE);
  			spin_unlock(&c->erase_completion_lock);
  			jffs2_dbg(1, "%s(): sleeping...
  ", __func__);
  			schedule();
  		} else
  			spin_unlock(&c->erase_completion_lock);
  			
  
  		/* Problem - immediately after bootup, the GCD spends a lot
  		 * of time in places like jffs2_kill_fragtree(); so much so
  		 * that userspace processes (like gdm and X) are starved
  		 * despite plenty of cond_resched()s and renicing.  Yield()
  		 * doesn't help, either (presumably because userspace and GCD
  		 * are generally competing for a higher latency resource -
  		 * disk).
  		 * This forces the GCD to slow the hell down.   Pulling an
  		 * inode in with read_inode() is much preferable to having
  		 * the GC thread get there first. */
  		schedule_timeout_interruptible(msecs_to_jiffies(50));
  
  		if (kthread_should_stop()) {
  			jffs2_dbg(1, "%s(): kthread_stop() called
  ", __func__);
  			goto die;
  		}
  
  		/* Put_super will send a SIGKILL and then wait on the sem.
  		 */
  		while (signal_pending(current) || freezing(current)) {
  			siginfo_t info;
  			unsigned long signr;
  
  			if (try_to_freeze())
  				goto again;
  
  			signr = dequeue_signal_lock(current, &current->blocked, &info);
  
  			switch(signr) {
  			case SIGSTOP:
  				jffs2_dbg(1, "%s(): SIGSTOP received
  ",
  					  __func__);
  				set_current_state(TASK_STOPPED);
  				schedule();
  				break;
  
  			case SIGKILL:
  				jffs2_dbg(1, "%s(): SIGKILL received
  ",
  					  __func__);
  				goto die;
  
  			case SIGHUP:
  				jffs2_dbg(1, "%s(): SIGHUP received
  ",
  					  __func__);
  				break;
  			default:
  				jffs2_dbg(1, "%s(): signal %ld received
  ",
  					  __func__, signr);
  			}
  		}
  		/* We don't want SIGHUP to interrupt us. STOP and KILL are OK though. */
  		disallow_signal(SIGHUP);
  
  		jffs2_dbg(1, "%s(): pass
  ", __func__);
  		if (jffs2_garbage_collect_pass(c) == -ENOSPC) {
  			pr_notice("No space for garbage collection. Aborting GC thread
  ");
  			goto die;
  		}
  	}
   die:
  	spin_lock(&c->erase_completion_lock);
  	c->gc_task = NULL;
  	spin_unlock(&c->erase_completion_lock);
  	complete_and_exit(&c->gc_thread_exit, 0);
  }