xfile.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include "all.h"

static Xfile *	xflfree;
static Xfid *	xfdfree;

#define	FIDMOD	127	/* prime */

static Xfile	*xfiles[FIDMOD];
static Lock	xlocks[FIDMOD];

Xfile *
xfile(Qid *qid, void *s, int new)
{
	int k;
	Xfile **hp, *f, *pf;

	k = ((ulong)qid->path ^ (((u32int)(uintptr)s)<<24))%FIDMOD;
	hp = &xfiles[k];

	lock(&xlocks[k]);
	for(f=*hp, pf=0; f; pf=f, f=f->next)
		if(f->qid.path == qid->path 
		&& (u32int)(uintptr)f->s == (u32int)(uintptr)s)
			break;
	if(f && pf){
		pf->next = f->next;
		f->next = *hp;
		*hp = f;
	}
	if(new < 0 && f){
		*hp = f->next;
		f->next = xflfree;
		xflfree = f;
		f = 0;
	}
	if(new > 0 && !f){
		if(!(f = xflfree))	/* assign = */
			f = listalloc(1024/sizeof(Xfile), sizeof(Xfile));
		xflfree = f->next;
		memset(f, 0, sizeof(Xfile));
		f->next = *hp;
		*hp = f;
		f->qid = *qid;
		f->s = s;
	}
	unlock(&xlocks[k]);
	return f;
}

Xfid *
xfid(char *uid, Xfile *xp, int new)
{
	Xfid *f, *pf;

	for(f=xp->users, pf=0; f; pf=f, f=f->next)
		if(f->uid[0] == uid[0] && strcmp(f->uid, uid) == 0)
			break;
	if(f && pf){
		pf->next = f->next;
		f->next = xp->users;
		xp->users = f;
	}
	if(new < 0 && f){
		if(f->urfid)
			clunkfid(xp->s, f->urfid);
		if(f->opfid)
			clunkfid(xp->s, f->opfid);
		xp->users = f->next;
		f->next = xfdfree;
		xfdfree = f;
		f = 0;
	}
	if(new > 0 && !f){
		if(!(f = xfdfree))	/* assign = */
			f = listalloc(1024/sizeof(Xfid), sizeof(Xfid));
		xfdfree = f->next;
		memset(f, 0, sizeof(Xfid));
		f->next = xp->users;
		xp->users = f;
		f->xp = xp;
		f->uid = strstore(uid);
		f->urfid = 0;
		f->opfid = 0;
	}
	return f;
}

int
xfpurgeuid(Session *s, char *uid)
{
	Xfile **hp, *f;
	Xfid *xf;
	int k, count=0;

	for(k=0; k<FIDMOD; k++){
		lock(&xlocks[k]);
		hp=&xfiles[k];
		for(f=*hp; f; f=f->next)
			if(f->s == s && (xf = xfid(uid, f, 0))){ /* assign = */
				xfclear(xf);
				++count;
			}
		unlock(&xlocks[k]);
	}
	return count;
}