/* $Id: waitqueue-r0drv-linux.h 109033 2016-07-22 18:27:37Z bird $ */
/** @file
 * IPRT - Linux Ring-0 Driver Helpers for Abstracting Wait Queues,
 */

/*
 * Copyright (C) 2006-2016 Oracle Corporation
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License (GPL) as published by the Free Software
 * Foundation, in version 2 as it comes in the "COPYING" file of the
 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
 *
 * The contents of this file may alternatively be used under the terms
 * of the Common Development and Distribution License Version 1.0
 * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
 * VirtualBox OSE distribution, in which case the provisions of the
 * CDDL are applicable instead of those of the GPL.
 *
 * You may elect to license modified versions of this file under the
 * terms and conditions of either the GPL or the CDDL or both.
 */

#ifndef ___r0drv_linux_waitqueue_r0drv_linux_h
#define ___r0drv_linux_waitqueue_r0drv_linux_h

#include "the-linux-kernel.h"

#include <iprt/asm-math.h>
#include <iprt/err.h>
#include <iprt/string.h>
#include <iprt/time.h>

/** The resolution (nanoseconds) specified when using
 *  schedule_hrtimeout_range. */
#define RTR0SEMLNXWAIT_RESOLUTION   50000

/**
 * Kernel mode Linux wait state structure.
 */
typedef struct RTR0SEMLNXWAIT {
    /** The wait queue entry. */
	wait_queue_t WaitQE;
    /** The absolute timeout given as nano seconds since the start of the
     *  monotonic clock. */
	uint64_t uNsAbsTimeout;
    /** The timeout in nano seconds relative to the start of the wait. */
	uint64_t cNsRelTimeout;
    /** The native timeout value. */
	union {
#ifdef IPRT_LINUX_HAS_HRTIMER
	/** The timeout when fHighRes is true. Absolute, so no updating. */
		ktime_t KtTimeout;
#endif
	/** The timeout when fHighRes is false.  Updated after waiting. */
		long lTimeout;
	} u;
    /** Set if we use high resolution timeouts. */
	bool fHighRes;
    /** Set if it's an indefinite wait. */
	bool fIndefinite;
    /** Set if we've already timed out.
     * Set by rtR0SemLnxWaitDoIt and read by rtR0SemLnxWaitHasTimedOut. */
	bool fTimedOut;
    /** TASK_INTERRUPTIBLE or TASK_UNINTERRUPTIBLE. */
	int iWaitState;
    /** The wait queue. */
	wait_queue_head_t *pWaitQueue;
} RTR0SEMLNXWAIT;
/** Pointer to a linux wait state. */
typedef RTR0SEMLNXWAIT *PRTR0SEMLNXWAIT;

/**
 * Initializes a wait.
 *
 * The caller MUST check the wait condition BEFORE calling this function or the
 * timeout logic will be flawed.
 *
 * @returns VINF_SUCCESS or VERR_TIMEOUT.
 * @param   pWait               The wait structure.
 * @param   fFlags              The wait flags.
 * @param   uTimeout            The timeout.
 * @param   pWaitQueue          The wait queue head.
 */
DECLINLINE(int) rtR0SemLnxWaitInit(PRTR0SEMLNXWAIT pWait, uint32_t fFlags,
				   uint64_t uTimeout,
				   wait_queue_head_t * pWaitQueue)
{
	/*
	 * Process the flags and timeout.
	 */
	if (!(fFlags & RTSEMWAIT_FLAGS_INDEFINITE)) {
/** @todo optimize: millisecs -> nanosecs -> millisec -> jiffies */
		if (fFlags & RTSEMWAIT_FLAGS_MILLISECS)
			uTimeout =
			    uTimeout <
			    UINT64_MAX / RT_US_1SEC * RT_US_1SEC ? uTimeout *
			    RT_US_1SEC : UINT64_MAX;
		if (uTimeout == UINT64_MAX)
			fFlags |= RTSEMWAIT_FLAGS_INDEFINITE;
		else {
			uint64_t u64Now;
			if (fFlags & RTSEMWAIT_FLAGS_RELATIVE) {
				if (uTimeout == 0)
					return VERR_TIMEOUT;

				u64Now = RTTimeSystemNanoTS();
				pWait->cNsRelTimeout = uTimeout;
				pWait->uNsAbsTimeout = u64Now + uTimeout;
				if (pWait->uNsAbsTimeout < u64Now)	/* overflow */
					fFlags |= RTSEMWAIT_FLAGS_INDEFINITE;
			} else {
				u64Now = RTTimeSystemNanoTS();
				if (u64Now >= uTimeout)
					return VERR_TIMEOUT;

				pWait->cNsRelTimeout = uTimeout - u64Now;
				pWait->uNsAbsTimeout = uTimeout;
			}
		}
	}

	if (!(fFlags & RTSEMWAIT_FLAGS_INDEFINITE)) {
		pWait->fIndefinite = false;
#ifdef IPRT_LINUX_HAS_HRTIMER
		if ((fFlags &
		     (RTSEMWAIT_FLAGS_NANOSECS | RTSEMWAIT_FLAGS_ABSOLUTE))
		    || pWait->cNsRelTimeout < RT_NS_1SEC / HZ * 4) {
			pWait->fHighRes = true;
# if BITS_PER_LONG < 64
			if (KTIME_SEC_MAX <= LONG_MAX
			    && pWait->uNsAbsTimeout >=
			    KTIME_SEC_MAX * RT_NS_1SEC_64 + (RT_NS_1SEC - 1))
				fFlags |= RTSEMWAIT_FLAGS_INDEFINITE;
			else
# endif
				pWait->u.KtTimeout =
				    ns_to_ktime(pWait->uNsAbsTimeout);
		} else
#endif
		{
			uint64_t cJiffies =
			    ASMMultU64ByU32DivByU32(pWait->cNsRelTimeout, HZ,
						    RT_NS_1SEC);
			if (cJiffies >= MAX_JIFFY_OFFSET)
				fFlags |= RTSEMWAIT_FLAGS_INDEFINITE;
			else {
				pWait->u.lTimeout = (long)cJiffies;
				pWait->fHighRes = false;
			}
		}
	}

	if (fFlags & RTSEMWAIT_FLAGS_INDEFINITE) {
		pWait->fIndefinite = true;
		pWait->fHighRes = false;
		pWait->uNsAbsTimeout = UINT64_MAX;
		pWait->cNsRelTimeout = UINT64_MAX;
		pWait->u.lTimeout = LONG_MAX;
	}

	pWait->fTimedOut = false;

	/*
	 * Initialize the wait queue related bits.
	 */
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 5, 39)
	init_wait((&pWait->WaitQE));
#else
	RT_ZERO(pWait->WaitQE);
	init_waitqueue_entry((&pWait->WaitQE), current);
#endif
	pWait->pWaitQueue = pWaitQueue;
	pWait->iWaitState = fFlags & RTSEMWAIT_FLAGS_INTERRUPTIBLE
	    ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;

	return VINF_SUCCESS;
}

/**
 * Prepares the next wait.
 *
 * This must be called before rtR0SemLnxWaitDoIt, and the caller should check
 * the exit conditions in-between the two calls.
 *
 * @param   pWait               The wait structure.
 */
DECLINLINE(void)rtR0SemLnxWaitPrepare(PRTR0SEMLNXWAIT pWait)
{
	/* Make everything thru schedule*() atomic scheduling wise. (Is this correct?) */
	prepare_to_wait(pWait->pWaitQueue, &pWait->WaitQE, pWait->iWaitState);
}

/**
 * Do the actual wait.
 *
 * @param   pWait               The wait structure.
 */
DECLINLINE(void) rtR0SemLnxWaitDoIt(PRTR0SEMLNXWAIT pWait)
{
	if (pWait->fIndefinite)
		schedule();
#ifdef IPRT_LINUX_HAS_HRTIMER
	else if (pWait->fHighRes) {
		int rc =
		    schedule_hrtimeout_range(&pWait->u.KtTimeout,
					     HRTIMER_MODE_ABS,
					     RTR0SEMLNXWAIT_RESOLUTION);
		if (!rc)
			pWait->fTimedOut = true;
	}
#endif
	else {
		pWait->u.lTimeout = schedule_timeout(pWait->u.lTimeout);
		if (pWait->u.lTimeout <= 0)
			pWait->fTimedOut = true;
	}
	after_wait((&pWait->WaitQE));
}

/**
 * Checks if a linux wait was interrupted.
 *
 * @returns true / false
 * @param   pWait               The wait structure.
 * @remarks This shall be called before the first rtR0SemLnxWaitDoIt().
 */
DECLINLINE(bool) rtR0SemLnxWaitWasInterrupted(PRTR0SEMLNXWAIT pWait)
{
	return pWait->iWaitState == TASK_INTERRUPTIBLE
	    && signal_pending(current);
}

/**
 * Checks if a linux wait has timed out.
 *
 * @returns true / false
 * @param   pWait               The wait structure.
 */
DECLINLINE(bool) rtR0SemLnxWaitHasTimedOut(PRTR0SEMLNXWAIT pWait)
{
	return pWait->fTimedOut;
}

/**
 * Deletes a linux wait.
 *
 * @param   pWait               The wait structure.
 */
DECLINLINE(void)rtR0SemLnxWaitDelete(PRTR0SEMLNXWAIT pWait)
{
	finish_wait(pWait->pWaitQueue, &pWait->WaitQE);
}

/**
 * Gets the max resolution of the timeout machinery.
 *
 * @returns Resolution specified in nanoseconds.
 */
DECLINLINE(uint32_t) rtR0SemLnxWaitGetResolution(void)
{
#ifdef IPRT_LINUX_HAS_HRTIMER
	return RTR0SEMLNXWAIT_RESOLUTION;
#else
	return RT_NS_1SEC / HZ;	/* ns */
#endif
}

#endif
