srv.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 <u.h>
#include <libc.h>
#include <auth.h>
#include <fcall.h>
#include <thread.h>
#include <9p.h>

void (*_forker)(void(*)(void*), void*, int);

static char Ebadattach[] = "unknown specifier in attach";
static char Ebadoffset[] = "bad offset";
static char Ebadcount[] = "bad count";
static char Ebotch[] = "9P protocol botch";
static char Ecreatenondir[] = "create in non-directory";
static char Edupfid[] = "duplicate fid";
static char Eduptag[] = "duplicate tag";
static char Eisdir[] = "is a directory";
static char Enocreate[] = "create prohibited";
static char Enomem[] = "out of memory";
static char Enoremove[] = "remove prohibited";
static char Enostat[] = "stat prohibited";
static char Enotfound[] = "file not found";
static char Enowrite[] = "write prohibited";
static char Enowstat[] = "wstat prohibited";
static char Eperm[] = "permission denied";
static char Eunknownfid[] = "unknown fid";
static char Ebaddir[] = "bad directory in wstat";
static char Ewalknodir[] = "walk in non-directory";

static void
setfcallerror(Fcall *f, char *err)
{
	f->ename = err;
	f->type = Rerror;
}

static void
changemsize(Srv *srv, int msize)
{
	if(srv->rbuf && srv->wbuf && srv->msize == msize)
		return;
	qlock(&srv->rlock);
	qlock(&srv->wlock);
	srv->msize = msize;
	free(srv->rbuf);
	free(srv->wbuf);
	srv->rbuf = emalloc9p(msize);
	srv->wbuf = emalloc9p(msize);
	qunlock(&srv->rlock);
	qunlock(&srv->wlock);
}

static Req*
getreq(Srv *s)
{
	long n;
	uchar *buf;
	Fcall f;
	Req *r;

	qlock(&s->rlock);
	if((n = read9pmsg(s->infd, s->rbuf, s->msize)) <= 0){
		qunlock(&s->rlock);
		return nil;
	}

	buf = emalloc9p(n);
	memmove(buf, s->rbuf, n);
	qunlock(&s->rlock);

	if(convM2S(buf, n, &f) != n){
		free(buf);
		return nil;
	}

	if((r=allocreq(s->rpool, f.tag)) == nil){	/* duplicate tag: cons up a fake Req */
		r = emalloc9p(sizeof *r);
		incref(&r->ref);
		r->tag = f.tag;
		r->ifcall = f;
		r->error = Eduptag;
		r->buf = buf;
		r->responded = 0;
		r->type = 0;
		r->srv = s;
		r->pool = nil;
if(chatty9p)
	fprint(2, "<-%d- %F: dup tag\n", s->infd, &f);
		return r;
	}

	r->srv = s;
	r->responded = 0;
	r->buf = buf;
	r->ifcall = f;
	memset(&r->ofcall, 0, sizeof r->ofcall);
	r->type = r->ifcall.type;

if(chatty9p)
	if(r->error)
		fprint(2, "<-%d- %F: %s\n", s->infd, &r->ifcall, r->error);
	else	
		fprint(2, "<-%d- %F\n", s->infd, &r->ifcall);

	return r;
}

static void
filewalk(Req *r)
{
	int i;
	File *f;

	f = r->fid->file;
	assert(f != nil);

	incref(f);
	for(i=0; i<r->ifcall.nwname; i++)
		if(f = walkfile(f, r->ifcall.wname[i]))
			r->ofcall.wqid[i] = f->qid;
		else
			break;

	r->ofcall.nwqid = i;
	if(f){
		r->newfid->file = f;
		r->newfid->qid = r->newfid->file->qid;
	}
	respond(r, nil);
}

void
walkandclone(Req *r, char *(*walk1)(Fid*, char*, void*), char *(*clone)(Fid*, Fid*, void*), void *arg)
{
	int i;
	char *e;

	if(r->fid == r->newfid && r->ifcall.nwname > 1){
		respond(r, "lib9p: unused documented feature not implemented");
		return;
	}

	if(r->fid != r->newfid){
		r->newfid->qid = r->fid->qid;
		if(clone && (e = clone(r->fid, r->newfid, arg))){
			respond(r, e);
			return;
		}
	}

	e = nil;
	for(i=0; i<r->ifcall.nwname; i++){
		if(e = walk1(r->newfid, r->ifcall.wname[i], arg))
			break;
		r->ofcall.wqid[i] = r->newfid->qid;
	}

	r->ofcall.nwqid = i;
	if(e && i==0)
		respond(r, e);
	else
		respond(r, nil);
}

static void
sversion(Srv*, Req *r)
{
	if(strncmp(r->ifcall.version, "9P", 2) != 0){
		r->ofcall.version = "unknown";
		respond(r, nil);
		return;
	}

	r->ofcall.version = "9P2000";
	r->ofcall.msize = r->ifcall.msize;
	respond(r, nil);
}
static void
rversion(Req *r, char *error)
{
	assert(error == nil);
	changemsize(r->srv, r->ofcall.msize);
}

static void
sauth(Srv *srv, Req *r)
{
	char e[ERRMAX];

	if((r->afid = allocfid(srv->fpool, r->ifcall.afid)) == nil){
		respond(r, Edupfid);
		return;
	}
	if(srv->auth)
		srv->auth(r);
	else{
		snprint(e, sizeof e, "%s: authentication not required", argv0);
		respond(r, e);
	}
}
static void
rauth(Req *r, char *error)
{
	if(error && r->afid)
		closefid(removefid(r->srv->fpool, r->afid->fid));
}

static void
sattach(Srv *srv, Req *r)
{
	if((r->fid = allocfid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Edupfid);
		return;
	}
	r->afid = nil;
	if(r->ifcall.afid != NOFID && (r->afid = lookupfid(srv->fpool, r->ifcall.afid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	r->fid->uid = estrdup9p(r->ifcall.uname);
	if(srv->tree){
		r->fid->file = srv->tree->root;
		incref(r->fid->file);
		r->ofcall.qid = r->fid->file->qid;
		r->fid->qid = r->ofcall.qid;
	}
	if(srv->attach)
		srv->attach(r);
	else
		respond(r, nil);
	return;
}
static void
rattach(Req *r, char *error)
{
	if(error && r->fid)
		closefid(removefid(r->srv->fpool, r->fid->fid));
}

static void
sflush(Srv *srv, Req *r)
{
	r->oldreq = lookupreq(srv->rpool, r->ifcall.oldtag);
	if(r->oldreq == nil || r->oldreq == r)
		respond(r, nil);
	else if(srv->flush)
		srv->flush(r);
	else
		respond(r, nil);
}
static int
rflush(Req *r, char *error)
{
	Req *or;

	assert(error == nil);
	or = r->oldreq;
	if(or){
		qlock(&or->lk);
		if(or->responded == 0){
			or->flush = erealloc9p(or->flush, (or->nflush+1)*sizeof(or->flush[0]));
			or->flush[or->nflush++] = r;
			qunlock(&or->lk);
			return -1;		/* delay response until or is responded */
		}
		qunlock(&or->lk);
		closereq(or);
	}
	r->oldreq = nil;
	return 0;
}

static char*
oldwalk1(Fid *fid, char *name, void *arg)
{
	char *e;
	Qid qid;
	Srv *srv;

	srv = arg;
	e = srv->walk1(fid, name, &qid);
	if(e)
		return e;
	fid->qid = qid;
	return nil;
}

static char*
oldclone(Fid *fid, Fid *newfid, void *arg)
{
	Srv *srv;

	srv = arg;
	if(srv->clone == nil)
		return nil;
	return srv->clone(fid, newfid);
}

static void
swalk(Srv *srv, Req *r)
{
	if((r->fid = lookupfid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	if(r->fid->omode != -1){
		respond(r, "cannot clone open fid");
		return;
	}
	if(r->ifcall.nwname && !(r->fid->qid.type&QTDIR)){
		respond(r, Ewalknodir);
		return;
	}
	if(r->ifcall.fid != r->ifcall.newfid){
		if((r->newfid = allocfid(srv->fpool, r->ifcall.newfid)) == nil){
			respond(r, Edupfid);
			return;
		}
		r->newfid->uid = estrdup9p(r->fid->uid);
	}else{
		incref(&r->fid->ref);
		r->newfid = r->fid;
	}
	if(r->fid->file){
		filewalk(r);
	}else if(srv->walk1)
		walkandclone(r, oldwalk1, oldclone, srv);
	else if(srv->walk)
		srv->walk(r);
	else
		sysfatal("no walk function, no file trees");
}
static void
rwalk(Req *r, char *error)
{
	if(error || r->ofcall.nwqid < r->ifcall.nwname){
		if(r->ifcall.fid != r->ifcall.newfid && r->newfid)
			closefid(removefid(r->srv->fpool, r->newfid->fid));
		if (r->ofcall.nwqid==0){
			if(error==nil && r->ifcall.nwname!=0)
				r->error = Enotfound;
		}else
			r->error = nil;	// No error on partial walks
	}else{
		if(r->ofcall.nwqid == 0){
			/* Just a clone */
			r->newfid->qid = r->fid->qid;
		}else{
			/* if file trees are in use, filewalk took care of the rest */
			r->newfid->qid = r->ofcall.wqid[r->ofcall.nwqid-1];
		}
	}
}

static void
sopen(Srv *srv, Req *r)
{
	int p;

	if((r->fid = lookupfid(srv->fpool, r->ifcall.fid)) == nil){
		respond(r, Eunknownfid);
		return;
	}
	if(r->fid->omode != -1){
		respond(r, Ebotch);
		return;
	}
	if((r->fid->qid.type&QTDIR) && (r->ifcall.mode&~ORCLOSE) != OREAD){
		respond(r, Eisdir);
		return;
	}
	r->ofcall.qid = r->fid->qid;
	switch(r->ifcall.mode&3){
	default:
		assert(0);
	case OREAD:
		p = AREAD;	
		break;
	case OWRITE:
		p = AWRITE;
		break;
	case ORDWR:
		p = AREAD|AWRITE;
		break;
	case OEXEC:
		p = AEXEC;	
		break;
	}
	if(r->ifcall.mode&OTRUNC)
		p |= AWRITE;
	if((r->fid->qid.type&QTDIR) && p!=AREAD){
		respond(r, Eperm);
		return;
	}
	if(r->fid->file){
		if(!hasperm(r->fid->file, r->fid->uid, p)){
			respond(r, Eperm);
			return;
		}
	/* BUG RACE */
		if((r->ifcall.mode&ORCLOSE)
		&& !hasperm(r->fid->file->parent, r->fid->uid, AWRITE)){
			respond(r, Eperm);
			return;
		}
		r->ofcall.qid = r->fid->file->qid;
		if((r->ofcall.qid.type&QTDIR)
		&& (r->fid->rdir = opendirfile(r->fid->file)) == nil){
			respond(r, "opendirfile failed");
			return;
		}
	}
	if(srv->open)
		srv->open(r);
	else
		respond(r, nil);
}
static void
ropen(Req *r, char *error)
{
	char errbuf[ERRMAX];
	if(error)
		return;
	if(chatty9p){
		snprint(errbuf, sizeof errbuf, "fid mode is 0x%ux\n", r->ifcall.mode);
		write(2, errbuf, strlen(errbuf));
	}
	r->fid->omode = r->ifcall.mode;