/*  * This file is part of the UCB release of Plan 9. It is subject to the license * terms in the LICENSE file found in the top-level directory of this * distribution and at http://akaros.cs.berkeley.edu/files/Plan9License. No * part of the UCB release of Plan 9, including this file, may be copied, * modified, propagated, or distributed except according to the terms contained * in the LICENSE file. */ #include "stdinc.h" #include "9.h" static struct {	VtLock*	lock; 	Excl*	head;	Excl*	tail;} ebox; struct Excl {	Fsys*	fsys;	uvlong	path;	ulong	time; 	Excl*	next;	Excl*	prev;}; enum {	LifeTime	= (5*60),}; intexclAlloc(Fid* fid){	ulong t;	Excl *excl; 	assert(fid->excl == nil); 	t = time(0L);	vtLock(ebox.lock);	for(excl = ebox.head; excl != nil; excl = excl->next){		if(excl->fsys != fid->fsys || excl->path != fid->qid.path)			continue;		/*		 * Found it.		 * Now, check if it's timed out.		 * If not, return error, it's locked.		 * If it has timed out, zap the old		 * one and continue on to allocate a		 * a new one.		 */		if(excl->time >= t){			vtUnlock(ebox.lock);			vtSetError("exclusive lock");			return 0;		}		excl->fsys = nil;	} 	/*	 * Not found or timed-out.	 * Alloc a new one and initialise.	 */	excl = vtMemAllocZ(sizeof(Excl));	excl->fsys = fid->fsys;	excl->path = fid->qid.path;	excl->time = t+LifeTime;	if(ebox.tail != nil){		excl->prev = ebox.tail;		ebox.tail->next = excl;	}	else{		ebox.head = excl;		excl->prev = nil;	}	ebox.tail = excl;	excl->next = nil;	vtUnlock(ebox.lock); 	fid->excl = excl;	return 1;} intexclUpdate(Fid* fid){	ulong t;	Excl *excl; 	excl = fid->excl; 	t = time(0L);	vtLock(ebox.lock);	if(excl->time < t || excl->fsys != fid->fsys){		vtUnlock(ebox.lock);		vtSetError("exclusive lock broken");		return 0;	}	excl->time = t+LifeTime;	vtUnlock(ebox.lock); 	return 1;} voidexclFree(Fid* fid){	Excl *excl; 	if((excl = fid->excl) == nil)		return;	fid->excl = nil; 	vtLock(ebox.lock);	if(excl->prev != nil)		excl->prev->next = excl->next;	else		ebox.head = excl->next;	if(excl->next != nil)		excl->next->prev = excl->prev;	else		ebox.tail = excl->prev;	vtUnlock(ebox.lock); 	vtMemFree(excl);} voidexclInit(void){	ebox.lock = vtLockAlloc();}