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#include "stdinc.h"
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#include "9.h"
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static struct {
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	VtLock*	lock;
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	Excl*	head;
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	Excl*	tail;
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} ebox;
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struct Excl {
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	Fsys*	fsys;
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	uvlong	path;
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	ulong	time;
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	Excl*	next;
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	Excl*	prev;
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};
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enum {
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	LifeTime	= (5*60),
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};
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int
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exclAlloc(Fid* fid)
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{
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	ulong t;
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	Excl *excl;
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	assert(fid->excl == nil);
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	t = time(0L);
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	vtLock(ebox.lock);
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	for(excl = ebox.head; excl != nil; excl = excl->next){
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		if(excl->fsys != fid->fsys || excl->path != fid->qid.path)
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			continue;
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		/*
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		 * Found it.
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		 * Now, check if it's timed out.
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		 * If not, return error, it's locked.
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		 * If it has timed out, zap the old
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		 * one and continue on to allocate a
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		 * a new one.
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		 */
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		if(excl->time >= t){
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			vtUnlock(ebox.lock);
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			vtSetError("exclusive lock");
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			return 0;
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		}
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		excl->fsys = nil;
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	}
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	/*
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	 * Not found or timed-out.
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	 * Alloc a new one and initialise.
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	 */
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	excl = vtMemAllocZ(sizeof(Excl));
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	excl->fsys = fid->fsys;
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	excl->path = fid->qid.path;
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	excl->time = t+LifeTime;
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	if(ebox.tail != nil){
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		excl->prev = ebox.tail;
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		ebox.tail->next = excl;
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	}
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	else{
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		ebox.head = excl;
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		excl->prev = nil;
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	}
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	ebox.tail = excl;
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	excl->next = nil;
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	vtUnlock(ebox.lock);
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	fid->excl = excl;
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	return 1;
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}
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int
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exclUpdate(Fid* fid)
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{
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	ulong t;
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	Excl *excl;
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	excl = fid->excl;
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	t = time(0L);
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	vtLock(ebox.lock);
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	if(excl->time < t || excl->fsys != fid->fsys){
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		vtUnlock(ebox.lock);
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		vtSetError("exclusive lock broken");
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		return 0;
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	}
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	excl->time = t+LifeTime;
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	vtUnlock(ebox.lock);
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	return 1;
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}
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void
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exclFree(Fid* fid)
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{
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	Excl *excl;
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	if((excl = fid->excl) == nil)
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		return;
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	fid->excl = nil;
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	vtLock(ebox.lock);
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	if(excl->prev != nil)
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		excl->prev->next = excl->next;
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	else
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		ebox.head = excl->next;
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	if(excl->next != nil)
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		excl->next->prev = excl->prev;
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	else
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		ebox.tail = excl->prev;
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	vtUnlock(ebox.lock);
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	vtMemFree(excl);
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}
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void
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exclInit(void)
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{
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	ebox.lock = vtLockAlloc();
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}