/*-
 * Copyright (c) 2017 Hans Petter Selasky
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice unmodified, this list of conditions, and the following
 *    disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <linux/compat.h>
#include <linux/completion.h>
#include <linux/mm.h>
#include <linux/kthread.h>

#include <sys/kernel.h>
#include <sys/eventhandler.h>
#include <sys/malloc.h>

static eventhandler_tag linuxkpi_thread_dtor_tag;

static MALLOC_DEFINE(M_LINUX_CURRENT, "linuxcurrent", "LinuxKPI task structure");

int
linux_alloc_current(struct thread *td, int flags)
{
	struct proc *proc;
	struct thread *td_other;
	struct task_struct *ts;
	struct task_struct *ts_other;
	struct mm_struct *mm;
	struct mm_struct *mm_other;

	MPASS(td->td_lkpi_task == NULL);

	ts = malloc(sizeof(*ts), M_LINUX_CURRENT, flags | M_ZERO);
	if (ts == NULL)
		return (ENOMEM);

	mm = malloc(sizeof(*mm), M_LINUX_CURRENT, flags | M_ZERO);
	if (mm == NULL) {
		free(ts, M_LINUX_CURRENT);
		return (ENOMEM);
	}

	/* setup new task structure */
	atomic_set(&ts->kthread_flags, 0);
	ts->task_thread = td;
	ts->comm = td->td_name;
	ts->pid = td->td_tid;
	ts->group_leader = ts;
	atomic_set(&ts->usage, 1);
	atomic_set(&ts->state, TASK_RUNNING);
	init_completion(&ts->parked);
	init_completion(&ts->exited);

	proc = td->td_proc;

	/* check if another thread already has a mm_struct */
	PROC_LOCK(proc);
	FOREACH_THREAD_IN_PROC(proc, td_other) {
		ts_other = td_other->td_lkpi_task;
		if (ts_other == NULL)
			continue;

		mm_other = ts_other->mm;
		if (mm_other == NULL)
			continue;

		/* try to share other mm_struct */
		if (atomic_inc_not_zero(&mm_other->mm_users)) {
			/* set mm_struct pointer */
			ts->mm = mm_other;
			break;
		}
	}

	/* use allocated mm_struct as a fallback */
	if (ts->mm == NULL) {
		/* setup new mm_struct */
		init_rwsem(&mm->mmap_sem);
		atomic_set(&mm->mm_count, 1);
		atomic_set(&mm->mm_users, 1);
		/* set mm_struct pointer */
		ts->mm = mm;
		/* clear pointer to not free memory */
		mm = NULL;
	}

	/* store pointer to task struct */
	td->td_lkpi_task = ts;
	PROC_UNLOCK(proc);

	/* free mm_struct pointer, if any */
	free(mm, M_LINUX_CURRENT);

	return (0);
}

struct mm_struct *
linux_get_task_mm(struct task_struct *task)
{
	struct mm_struct *mm;

	mm = task->mm;
	if (mm != NULL) {
		atomic_inc(&mm->mm_users);
		return (mm);
	}
	return (NULL);
}

void
linux_mm_dtor(struct mm_struct *mm)
{
	free(mm, M_LINUX_CURRENT);
}

void
linux_free_current(struct task_struct *ts)
{
	mmput(ts->mm);
	free(ts, M_LINUX_CURRENT);
}

static void
linuxkpi_thread_dtor(void *arg __unused, struct thread *td)
{
	struct task_struct *ts;

	ts = td->td_lkpi_task;
	if (ts == NULL)
		return;

	td->td_lkpi_task = NULL;
	put_task_struct(ts);
}

struct task_struct *
linux_pid_task(pid_t pid)
{
	struct thread *td;
	struct proc *p;

	/* try to find corresponding thread */
	td = tdfind(pid, -1);
	if (td != NULL) {
		struct task_struct *ts = td->td_lkpi_task;
		PROC_UNLOCK(td->td_proc);
		return (ts);
	}

	/* try to find corresponding procedure */
	p = pfind(pid);
	if (p != NULL) {
		FOREACH_THREAD_IN_PROC(p, td) {
			struct task_struct *ts = td->td_lkpi_task;
			if (ts != NULL) {
				PROC_UNLOCK(p);
				return (ts);
			}
		}
		PROC_UNLOCK(p);
	}
	return (NULL);
}

struct task_struct *
linux_get_pid_task(pid_t pid)
{
	struct thread *td;
	struct proc *p;

	/* try to find corresponding thread */
	td = tdfind(pid, -1);
	if (td != NULL) {
		struct task_struct *ts = td->td_lkpi_task;
		if (ts != NULL)
			get_task_struct(ts);
		PROC_UNLOCK(td->td_proc);
		return (ts);
	}

	/* try to find corresponding procedure */
	p = pfind(pid);
	if (p != NULL) {
		FOREACH_THREAD_IN_PROC(p, td) {
			struct task_struct *ts = td->td_lkpi_task;
			if (ts != NULL) {
				get_task_struct(ts);
				PROC_UNLOCK(p);
				return (ts);
			}
		}
		PROC_UNLOCK(p);
	}
	return (NULL);
}

bool
linux_task_exiting(struct task_struct *task)
{
	struct proc *p;
	bool ret;

	ret = false;
	p = pfind(task->pid);
	if (p != NULL) {
		if ((p->p_flag & P_WEXIT) != 0)
			ret = true;
		PROC_UNLOCK(p);
	}
	return (ret);
}

static void
linux_current_init(void *arg __unused)
{
	lkpi_alloc_current = linux_alloc_current;
	linuxkpi_thread_dtor_tag = EVENTHANDLER_REGISTER(thread_dtor,
	    linuxkpi_thread_dtor, NULL, EVENTHANDLER_PRI_ANY);
}
SYSINIT(linux_current, SI_SUB_EVENTHANDLER, SI_ORDER_SECOND, linux_current_init, NULL);

static void
linux_current_uninit(void *arg __unused)
{
	struct proc *p;
	struct task_struct *ts;
	struct thread *td;

	sx_slock(&allproc_lock);
	FOREACH_PROC_IN_SYSTEM(p) {
		PROC_LOCK(p);
		FOREACH_THREAD_IN_PROC(p, td) {
			if ((ts = td->td_lkpi_task) != NULL) {
				td->td_lkpi_task = NULL;
				put_task_struct(ts);
			}
		}
		PROC_UNLOCK(p);
	}
	sx_sunlock(&allproc_lock);
	EVENTHANDLER_DEREGISTER(thread_dtor, linuxkpi_thread_dtor_tag);
	lkpi_alloc_current = linux_alloc_current_noop;
}
SYSUNINIT(linux_current, SI_SUB_EVENTHANDLER, SI_ORDER_SECOND, linux_current_uninit, NULL);