paqfs.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

paqDirFree(PaqDir *pd)
{
	if(pd == nil)
		return;
	free(pd->name);
	free(pd->uid);
	free(pd->gid);
	free(pd);
}

Qid
paqDirQid(PaqDir *d)
{
	Qid q;

	q.path = d->qid;
	q.vers = 0;
	q.type = d->mode >> 24;

	return q;
}

int
packDir(PaqDir *s, uchar *buf, int n)
{
	Dir dir;

	memset(&dir, 0, sizeof(dir));
	dir.qid = paqDirQid(s);
	dir.mode = s->mode;
	dir.atime = s->mtime;
	dir.mtime = s->mtime;
	dir.length = s->length;
	dir.name = s->name;
	dir.uid = s->uid;
	dir.gid = s->gid;
	dir.muid = s->uid;

	n = convD2M(&dir, buf, n);
	if(n < STATFIXLEN)
		return 0;
	return n;
}

Block *
blockLoad(ulong addr, int type)
{
	ulong age;
	int i, j;
	Block *b;

	if(addr == 0)
		return nil;

	cacheage++;

	/* age has wraped */
	if(cacheage == 0) {
		for(i=0; i<cachesize; i++)
			cache[i].age = 0;
	}

	j = -1;
	age = ~0;
	for(i=0; i<cachesize; i++) {
		b = &cache[i];
		if(b->age < age && b->ref == 0) {
			age = b->age;
			j = i;
		}
		if(b->addr != addr)
			continue;
		b->age = cacheage;
		b->ref++;
		return b;
	}
	if(j < 0)
		sysfatal("no empty spots in cache!\n");
	b = &cache[j];
	assert(b->ref == 0);

	if(!blockRead(b->data, addr, type)) {
		b->addr = 0;
		b->age = 0;
		return nil;
	}

	b->age = cacheage;
	b->addr = addr;
	b->ref = 1;
	
	return b;
}

void
blockFree(Block *b)
{
	if(b == nil)
		return;
	if(--b->ref > 0)
		return;
	assert(b->ref == 0);
}

Paq*
paqWalk(Paq *s, char *name)
{
	Block *ptr, *b;
	uchar *p, *ep;
	PaqDir *pd;
	int i, n;
	Paq *ss;

	if(strcmp(name, "..") == 0)
		return paqCpy(s->up);

	if(rootfile && s == root){
		if(strcmp(name, rootfile->dir->name) == 0)
			return paqCpy(rootfile);
		return nil;
	}

	ptr = blockLoad(s->dir->offset, PointerBlock);
	if(ptr == nil)
		return nil;

	for(i=0; i<blocksize/4; i++) {
		b = blockLoad(getl(ptr->data+i*4), DirBlock);
		if(b == nil)
			break;
		p = b->data;
		ep = p + blocksize;
		while(checkDirSize(p, ep)) {
			n = gets(p);
			pd = getDir(p);
			if(strcmp(pd->name, name) == 0) {
				ss = emallocz(sizeof(Paq));
				ss->ref = 1;
				ss->up = paqCpy(s);
				ss->dir = pd;
				ss->qid = paqDirQid(pd);
				blockFree(b);
				blockFree(ptr);
				return ss;
			}
			paqDirFree(pd);
			p += n;
		}
		blockFree(b);
	}

	blockFree(ptr);
	return nil;
}

Fid *
newfid(int fid)
{
	Fid *f, *ff;

	ff = 0;
	for(f = fids; f; f = f->next)
		if(f->fid == fid)
			return f;
		else if(!ff && !f->busy)
			ff = f;
	if(ff){
		ff->fid = fid;
		return ff;
	}
	f = emallocz(sizeof *f);
	f->fid = fid;
	f->next = fids;
	fids = f;
	return f;
}

void
io(int fd)
{
	char *err;
	int n, pid;
	uchar *mdata;

	mdata = emalloc(mesgsize);

	pid = getpid();

	for(;;){
		n = read9pmsg(fd, mdata, mesgsize);
		if(n < 0)
			sysfatal("mount read");
		if(n == 0)
			break;
		if(convM2S(mdata, n, &rhdr) == 0)
			continue;

		if(debug)
			fprint(2, "paqfs %d:<-%F\n", pid, &rhdr);

		thdr.data = (char*)mdata + IOHDRSZ;
		if(!fcalls[rhdr.type])
			err = "bad fcall type";
		else
			err = (*fcalls[rhdr.type])(newfid(rhdr.fid));
		if(err){
			thdr.type = Rerror;
			thdr.ename = err;
		}else{
			thdr.type = rhdr.type + 1;
			thdr.fid = rhdr.fid;
		}
		thdr.tag = rhdr.tag;
		if(debug)
			fprint(2, "paqfs %d:->%F\n", pid, &thdr);/**/
		n = convS2M(&thdr, mdata, mesgsize);
		if(n == 0)
			sysfatal("convS2M sysfatal on write");
		if(write(fd, mdata, n) != n)
			sysfatal("mount write");
	}
}

int
perm(PaqDir *s, char *user, int p)
{
	ulong perm = s->mode;

	if((p*Pother) & perm)
		return 1;
	if((noauth || strcmp(user, s->gid)==0) && ((p*Pgroup) & perm))
		return 1;
	if((noauth || strcmp(user, s->uid)==0) && ((p*Powner) & perm))
		return 1;
	return 0;
}

void
init(char *file, int verify)
{
	PaqHeader hdr;
	PaqTrailer tlr;
	Dir *dir;
	int i;
	uchar *p;
	DigestState *ds = nil;
	PaqDir *r;
	Block *b;
	ulong offset;

	inflateinit();

	bin = Bopen(file, OREAD);
	if(bin == nil)
		sysfatal("could not open file: %s: %r", file);
	if(verify)
		ds = sha1(0, 0, 0, 0);
	
	readHeader(&hdr, file, ds);
	blocksize = hdr.blocksize;

	if(verify) {
		readBlocks(file, ds);
	} else {
		dir = dirstat(file);
		if(dir == nil)
			sysfatal("could not stat file: %s: %r", file);
		offset = dir->length - TrailerSize;
		free(dir);
		if(Bseek(bin, offset, 0) != offset)
			sysfatal("could not seek to trailer: %s", file);
	}

	readTrailer(&tlr, file, ds);

	/* asctime includes a newline - yuk */
	fprint(2, "%s: %s", hdr.label, asctime(gmtime(hdr.time)));
	fprint(2, "fingerprint: ");
	for(i=0; i<20; i++)
		fprint(2, "%.2x", tlr.sha1[i]);
	fprint(2, "\n");

	cache = emallocz(cachesize*sizeof(Block));
	p = emalloc(cachesize*blocksize);
	for(i=0; i<cachesize; i++) {
		cache[i].data = p;
		p += blocksize;
	}

	/* hand craft root */
	b = blockLoad(tlr.root, DirBlock);
	if(b == nil || !checkDirSize(b->data, b->data+blocksize))
		sysfatal("could not read root block: %s", file);
	r = getDir(b->data);
	blockFree(b);
	root = emallocz(sizeof(Paq));
	root->qid = paqDirQid(r);
	root->ref = 1;
	root->dir = r;
	root->up = root;	/* parent of root is root */

	/* craft root directory if root is a normal file */
	if(!(root->qid.type&QTDIR)){
		rootfile = root;
		root = emallocz(sizeof(Paq));
		root->qid = rootfile->qid;
		root->qid.type |= QTDIR;
		root->qid.path++;
		root->ref = 1;
		root->dir = emallocz(sizeof(PaqDir));
		*root->dir = *r;
		root->dir->mode |= DMDIR|0111;
		root->up = root;
	}
}

int
blockRead(uchar *data, ulong addr, int type)
{
	uchar buf[BlockSize];
	PaqBlock b;
	uchar *cdat;

	if(Bseek(bin, addr, 0) != addr){
		fprint(2, "paqfs: seek %lud: %r\n", addr);
		return 0;
	}
	if(Bread(bin, buf, BlockSize) != BlockSize){
		fprint(2, "paqfs: read %d at %lud: %r\n", BlockSize, addr);
		return 0;
	}
	getBlock(buf, &b);
	if(b.magic != BlockMagic || b.size > blocksize || b.type != type){
		fprint(2, "paqfs: bad block: magic %.8lux (want %.8ux) size %lud (max %d) type %ud (want %ud)\n",
			b.magic, BlockMagic, b.size, blocksize, b.type, type);
		return 0;
	}

	switch(b.encoding) {
	default:
		return 0;
	case NoEnc:
		if(Bread(bin, data, blocksize) < blocksize)
			return 0;
		break;
	case DeflateEnc:
		cdat = emalloc(b.size);
		if(Bread(bin, cdat, b.size) < b.size) {
			free(cdat);
			return 0;
		}
		if(inflateblock(data, blocksize, cdat, b.size) < 0) {
			fprint(2, "inflate error: %r\n");
			free(cdat);
			return 0;
		}
		free(cdat);
		break;
	}
	if(adler32(0, data, blocksize) != b.adler32)
		return 0;
	return 1;
}

void
readHeader(PaqHeader *hdr, char *name, DigestState *ds)
{
	uchar buf[HeaderSize];
	
	if(Bread(bin, buf, HeaderSize) < HeaderSize)
		sysfatal("could not read header: %s: %r", name);
	if(ds)
		sha1(buf, HeaderSize, 0, ds);
	getHeader(buf, hdr);
	if(hdr->magic != HeaderMagic)
		sysfatal("bad header magic 0x%lux: %s", hdr->magic, name);
	if(hdr->version != Version)
		sysfatal("unknown file version: %s", name);
}

void
readBlocks(char *name, DigestState *ds)
{
	uchar *buf;
	PaqBlock b;

	buf = emalloc(BlockSize+blocksize);

	for(;;) {
		if(Bread(bin, buf, 4) < 4)
			sysfatal("could not read block: %s: %r", name);
		Bseek(bin, -4, 1);
		/* check if it is a data block */

		if(getl(buf) != BlockMagic)
			break;

		if(Bread(bin, buf, BlockSize) < BlockSize)
			sysfatal("could not read block: %s: %r", name);
		if(ds)
			sha1(buf, BlockSize, 0, ds);
		getBlock(buf, &b);

		if(b.size > blocksize)
			sysfatal("bad block size: %lud: %s", b.size, name);
		if(ds) {
			if(Bread(bin, buf, b.size) < b.size)
				sysfatal("sysfatal reading block: %s: %r", name);
			sha1(buf, b.size, 0, ds);
		} else
			Bseek(bin, b.size, 1);
	}

	free(buf);
}

void
readTrailer(PaqTrailer *tlr, char *name, DigestState *ds)
{
	uchar buf[TrailerSize];
	uchar digest[20];

	if(Bread(bin, buf, TrailerSize) < TrailerSize)
		sysfatal("could not read trailer: %s: %r", name);
	getTrailer(buf, tlr);
	if(tlr->magic != TrailerMagic)
		sysfatal("bad trailer magic: %s", name);
	if(ds) {
		sha1(buf, TrailerSize-20, digest, ds);
		if(memcmp(digest, tlr->sha1, 20) != 0)
			sysfatal("bad sha1 digest: %s", name);
	}
}

void *
emalloc(ulong n)
{
	void *p;

	p = malloc(n);
	if(!p)
		sysfatal("out of memory");
	return p;
}

void *
emallocz(ulong n)
{
	void *p;

	p = emalloc(n);
	memset(p, 0, n);

	return p;
}

void *
erealloc(void *p, ulong n)
{
	p = realloc(p, n);
	if(!p)
		sysfatal("out of memory");
	return p;
}

char *
estrdup(char *s)
{
	s = strdup(s);
	if(s == nil)
		sysfatal("out of memory");
	return s;
}


ulong
getl(uchar *p)
{
	return (p[0]<<24) | (p[1]<<16) | (p[2]<<8) | p[3];
}


int
gets(uchar *p)
{
	return (p[0]<<8) | p[1];
}

int
checkDirSize(uchar *p, uchar *ep)
{
	int n;	
	int i;

	if(ep-p < 2)
		return 0;
	n = gets(p);
	if(p+n > ep)
		return 0;
	ep = p+n;
	p += 22;
	for(i=0; i<3; i++) {
		if(p+2 > ep)
			return 0;
		n = gets(p);
		if(p+n > ep)
			return 0;
		p += n;
	}
	return 1;
}

void
getHeader(uchar *p, PaqHeader *h)
{
	h->magic = getl(p);
	h->version = gets(p+4);
	h->blocksize = gets(p+6);
	if((h->magic>>16) == BigHeaderMagic){
		h->magic = HeaderMagic;
		h->version = gets(p+2);
		h->blocksize = getl(p+4);
	}
	h->time = getl(p+8);
	memmove(h->label, p+12, sizeof(h->label));
	h->label[sizeof(h->label)-1] = 0;
}

void
getTrailer(uchar *p, PaqTrailer *t)
{
	t->magic = getl(p);
	t->root = getl(p+4);
	memmove(t->sha1, p+8, 20);
}

void
getBlock(uchar *p, PaqBlock *b)
{
	b->magic = getl(p);
	b->size = gets(p+4);
	if((b->magic>>16) == BigBlockMagic){
		b->magic = BlockMagic;
		b->size = getl(p+2);
	}
	b->type = p[6];
	b->encoding = p[7];
	b->adler32 = getl(p+8);
}

PaqDir *
getDir(uchar *p)
{
	PaqDir *pd;

	pd = emallocz(sizeof(PaqDir));
	pd->qid = getl(p+2);
	pd->mode = getl(p+6);
	pd->mtime = getl(p+10);
	pd->length = getl(p+14);
	pd->offset = getl(p+18);
	p += 22;
	pd->name = getstr(p);
	p += gets(p);
	pd->uid = getstr(p);
	p += gets(p);
	pd->gid = getstr(p);

	return pd;
}


char *
getstr(uchar *p)
{
	char *s;
	int n;

	n = gets(p);
	s = emalloc(n+1);
	memmove(s, p+2, n);
	s[n] = 0;
	return s;
}

void
usage(void)
{
	fprint(2, "usage: %s [-disv] [-c cachesize] [-m mountpoint] [-M mesgsize] paqfile\n", argv0);
	exits("usage");
}