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coherent

/*
 * coh/rlock.c
 * COHERENT record locking.
 * Modified 5/92 by steve from tsm's old source.
 * All record locking functions meet the system V standard.
 */

#include <sys/coherent.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/fd.h>
#include <sys/proc.h>
#include <sys/rlock.h>
#include <sys/sched.h>
#include <sys/uproc.h>
#include <unistd.h>

/* Globals. */
RLOCK	*freerl;
GATE	rlgate = { 0, 0};
unsigned RLOCKS = 100;			/* patchable */

/* Forward. */
int		rlock();
int		rlinit();
static	int	nextblock();
static	int	nextmeet();
static	RLOCK	*getlock();
static	RLOCK	*freelock();
static	int	extract();
static	int	remlock();
static	int	addlock();
static	int	waitlock();
static	int	waiting();

/*
 * Record locking.
 */
int
rlock(fdp, cmd, flp) register FD *fdp; register FLOCK *flp;
{
	register RLOCK	*org;
	register int	retval;
	RLOCK		srl;
	RLOCK		*rlp;

	org = (RLOCK *)&fdp->f_ip->i_rl;
	retval = -1;
	srl.rl_proc = SELF;
	srl.rl_type = flp->l_type==F_RDLCK ? 0:1;
	srl.rl_start = flp->l_start;
	if (flp->l_whence == SEEK_CUR)
		srl.rl_start += fdp->f_seek;
	else if (flp->l_whence == SEEK_END)
		srl.rl_start += fdp->f_ip->i_size;
	srl.rl_end = srl.rl_start;
	if (flp->l_len > 0)
		srl.rl_end += flp->l_len - 1;
	else if (flp->l_len == 0)
		srl.rl_end = -1;
	else {
		srl.rl_start += flp->l_len;
		srl.rl_end--;
	}
	if (srl.rl_start < 0  ||  srl.rl_end < -1
	    || srl.rl_end != -1 && srl.rl_start > srl.rl_end) {
		u.u_error = EINVAL;
		return -1;
	}
	lock(rlgate);
	rlp = org;
	if (cmd == F_GETLK) {
		if (!nextblock(&rlp, &srl))
			flp->l_type = F_UNLCK;
		else {
			flp->l_type = rlp->rl_type ? F_WRLCK:F_RDLCK;
			flp->l_whence = SEEK_SET;
			flp->l_start = rlp->rl_start;
			if (rlp->rl_end == -1)
				flp->l_len = 0;
			else
				flp->l_len = rlp->rl_end - flp->l_start + 1;
			flp->l_pid = rlp->rl_proc->p_pid;
		}
		retval = 0;
	} else if (flp->l_type == F_UNLCK)
		retval =  remlock(org, &srl);
	else if (srl.rl_type && !fdp->f_flag & IPW
	      || !srl.rl_type && !fdp->f_flag & IPR)
		u.u_error = EINVAL;
	else if (cmd == F_SETLKW)
		retval = waitlock(org, &srl);
	else if (!nextblock(&rlp, &srl))
		retval = addlock(org, &srl);
	else
		u.u_error = EAGAIN;
	unlock(rlgate);
	if (cmd != F_GETLK)
		wakeup(org);
	return retval;
}

/* Allocate and initialize free record lock list. */
int
rlinit()
{
	register RLOCK	*rl;

	if (RLOCKS == 0) {
		freerl = NULL;
		return 0;
	}
	freerl = kalloc(RLOCKS * sizeof(RLOCK));
	if (freerl == NULL)
		panic("rlinit: no space for RLOCKs");
	rl = &freerl[RLOCKS-1];
	rl->rl_next = NULL;
	while (--rl >= freerl)
		rl->rl_next = rl+1;
	return 1;
}

/*
 * Record locking subroutines.
 * Most of them assume that rlgate is locked.
 * The user is guaranteed no unwanted unlocks regardless of error.
 * rlgate is locked whenever the lock list contents or free list is used.
 * Be careful if you change anything that these things remain true.
 */

/*
 * In nextblock and nextmeet,
 * list is a ptr to an RLOCK * which is owned by the caller.
 * This allows calls to proceed down an rlock list.
 * These routines should NOT be called with *list == NULL.
 */

/* Set *list = next element in list conflicting with lock. */
static
int
nextblock(list, lock) register RLOCK **list, *lock;
{
	while (nextmeet(list, lock)) {
		if (lock->rl_proc != (*list)->rl_proc
		   && (lock->rl_type || (*list)->rl_type)) {
			return 1;
		}
	}
	return 0;
}

/* Set *list = next element of list referencing a loc referenced by lock */
static
int
nextmeet(list, lock) RLOCK **list, *lock;
{
	register RLOCK	*block;
	register long top, bot;

	top = lock->rl_start;
	bot = lock->rl_end;
	for (block = (*list)->rl_next; block != NULL; block = block->rl_next) {
		if (bot == -1) {
			if (block->rl_end == -1 || block->rl_end >= top)
				break;
		} else if (bot >= block->rl_start)
			if (block->rl_end == -1 || block->rl_end >= top)
				break;
	}
	if ((*list = block) != NULL)
		return 1;
	return 0;
}

/* Remove and return a lock from the free list. */
static
RLOCK *
getlock()
{
	register RLOCK *rl;

	rl = freerl;
	if (rl != NULL)
		freerl = rl->rl_next;
	else
		u.u_error = ENOLCK;
	return rl;
}

/*
 * Remove element from the lock list beginning at org and add it to the free list.
 * Return pointer to (what used to be) its predecessor.
 */
static
RLOCK *
freelock(org, elt) register RLOCK *org, *elt;
{
	while (elt != org->rl_next)
		org = org->rl_next;
	org->rl_next = elt->rl_next;
	elt->rl_next = freerl;
	freerl = elt;
	return org;
}

/*
 * Remove new lock from old. 
 * Returns:
 *	1 if caller should free old.
 *	0 if caller should do nothing.
 *	-1 if error (out of locks).
 */
static
int
extract(old, new) register RLOCK *old, *new;
{
	long		tend;
	register RLOCK	*lock;

	if (new->rl_start <= old->rl_start) {
		if (new->rl_end == -1
		   || old->rl_end != -1 && new->rl_end >= old->rl_end)
			return 1;
		old->rl_start = new->rl_end+1;
		return 0;
	}
	tend = old->rl_end;
	old->rl_end = new->rl_start - 1;
	if (new->rl_end == -1
	   ||  tend != -1  &&  new->rl_end >= tend)
		return 0;
	if ((lock = getlock()) == NULL) {
		old->rl_end = tend;
		return -1;
	}
	lock->rl_type = old->rl_type;
	lock->rl_proc = old->rl_proc;
	lock->rl_start = new->rl_end+1;
	lock->rl_end = tend;
	lock->rl_next = old->rl_next;
	old->rl_next = lock;
	return 0;
}

/* Extract lock from each element of list. */
static
int
remlock(list, lock) RLOCK *list; register RLOCK *lock;
{
	RLOCK *org;

	org = list;
	while (nextmeet(&list, lock)) {
		if (list->rl_proc != lock->rl_proc)
			continue;
		switch(extract(list, lock)) {
			case 1:
				list = freelock(org, list);
			case 0:
				break;
			default:
				return -1;
		}
	}
	return 0;
}

/*
 * Install lock in list.
 * Combine lock with neighbouring locks of same type and owner.
 * Get space for new lock (best done here - OK since rllock locked).
 * Remove old locks (always different type, same owner) and attach new lock.
 * To avoid removing desired locks, addlock allows redundant locks to appear.
 * This is always rectified by the future unlock and is rare.
 */
static
int
addlock(list, lock) RLOCK *list; register RLOCK *lock;
{
	RLOCK	*new, *org;
	register long top, bot;

	org = list;
	top = lock->rl_start;
	bot = lock->rl_end;
	if (top != 0)
		lock->rl_start--;
	if (bot != -1)
		lock->rl_end++;
	while (nextmeet(&list, lock)) {
		if (list->rl_proc != lock->rl_proc
		   || list->rl_type != lock->rl_type)
			continue;
		if (list->rl_start < top)
			top = list->rl_start;
		if (bot != -1 && (list->rl_end == -1 || list->rl_end >= bot))
				bot = list->rl_end;
		list = freelock(org, list);
	}
	if ((new = getlock()) == NULL)
		return -1;
	new->rl_proc = lock->rl_proc;
	new->rl_type = lock->rl_type;
	lock = new;
	lock->rl_start = top;
	lock->rl_end = bot;
	remlock(org, lock);
	lock->rl_next = org->rl_next;
	org->rl_next = lock;
	return 0;
}

/* Sleep until possible to install rl in list then do so. */
#define cleanup()  SELF->p_prl = NULL;  rl->rl_next = freerl;  freerl = rl
static
int
waitlock(list, srl) RLOCK *list, *srl;
{
	register RLOCK *org;

	org = list;
	if (nextblock(&list, srl)) {
		register RLOCK *rl = getlock();
	
		if (rl == NULL)
			return -1;
		*rl = *srl;
		rl->rl_next = org;
		SELF->p_prl = rl;
		do {
			do {
				if (waiting(list->rl_proc)) {
					u.u_error = EDEADLK;
					cleanup();
					return -1;
				}
			} while (nextblock(&list, rl));
			unlock(rlgate);
			x_sleep(org, primed, slpriSigCatch, "rlock");
			lock(rlgate);
			if (SELF->p_ssig && nondsig()) {
				u.u_error = EINTR;
				cleanup();
				return -1;
			}
			list = org;
		} while (nextblock(&list, rl));
		cleanup();
	}
	return addlock(org, srl);
}

/* True if pp has requested a lock (even indirectly) pending on SELF. */
static
int
waiting(pp) PROC *pp;
{
	RLOCK		*list;
	register RLOCK	*lock;

	lock = pp->p_prl;
	if (lock == NULL)
		return 0;
	list = lock->rl_next;
	while (nextblock(&list, lock)) {
		if (list->rl_proc == SELF)
			return 1;
		if (waiting(list->rl_proc))
			return 1;
	}
	return 0;
}

/* end of coh/rlock.c */

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