C++ Bread函数代码示例

void
statsinit(void)
{
	static Biobuf *b = nil;
	static int64_t filelen = 0;
	int64_t newlen;
	int iq, n, i, nstats = 0;
	uint8_t *s, buf[3+HINTmax*3];  /* iq, n, (url,prob)... */
	Hint *arena, *h;
	char *file;
	static void *oldarena = nil;

	file = "/sys/log/httpd/pathstat";
	if(b == nil){
		if(filelen == -1)
			return; /* if failed first time */
		b = Bopen(file, OREAD); /* first time */
		if(b == nil){
			syslog(0, HTTPLOG, "no %s, abandon prefetch hints", file);
			filelen = -1;
			return;
		}
	}
	newlen = Bfilelen(b); /* side effect: rewinds b */
	if(newlen == filelen || Bage(b)<300)
		return;
	filelen = newlen;
	if(oldarena){
		free(oldarena);
		memset(nhint,0,sizeof nhint);
	}
	arena = (Hint*)ezalloc((filelen/3)*sizeof(Hint));
	oldarena = arena;
	for(;;){
		i = Bread(b,buf,3);
		if(i<3)
			break;
		nstats++;
		iq = buf[0];
		iq = (iq<<8) | buf[1];
		n = buf[2];
		h = arena;
		arena += n;
		hints[iq] = h;
		nhint[iq] = n;
		if(Bread(b,buf,3*n)!=3*n)
			sysfatal("stats read error");
		for(i=0; i<n; i++){
			s = &buf[3*i];
			h[i].url = (s[0]<<8) | s[1];
			h[i].prob = s[2];
		}
	}
	syslog(0, HTTPLOG, "prefetch-hints stats=%d (%.1fMB)", nstats, 1.e-6*((filelen/3)*sizeof(Hint)));
}

int
_read5(Biobuf *bp, Prog *p)
{
	int as, n;
	Addr a;

	as = BGETC(bp);			/* as */
	if(as < 0)
		return 0;
	p->kind = aNone;
	p->sig = 0;
	if(as == ANAME || as == ASIGNAME){
		if(as == ASIGNAME){
			Bread(bp, &p->sig, 4);
			p->sig = leswal(p->sig);
		}
		p->kind = aName;
		p->type = type2char(BGETC(bp));		/* type */
		p->sym = BGETC(bp);			/* sym */
		n = 0;
		for(;;) {
			as = BGETC(bp);
			if(as < 0)
				return 0;
			n++;
			if(as == 0)
				break;
		}
		p->id = malloc(n);
		if(p->id == 0)
			return 0;
		Bseek(bp, -n, 1);
		if(Bread(bp, p->id, n) != n)
			return 0;
		return 1;
	}
	if(as == ATEXT)
		p->kind = aText;
	else if(as == AGLOBL)
		p->kind = aData;
	skip(bp, 6);		/* scond(1), reg(1), lineno(4) */
	a = addr(bp);
	addr(bp);
	if(a.type != D_OREG || a.name != D_STATIC && a.name != D_EXTERN)
		p->kind = aNone;
	p->sym = a.sym;
	return 1;
}

char*
winreadbody(Window *w, int *np)	/* can't use readfile because acme doesn't report the length */
{
	char *s;
	int m, na, n;

	if(w->body != nil)
		winclosebody(w);
	winopenbody(w, OREAD);
	s = nil;
	na = 0;
	n = 0;
	for(;;){
		if(na < n+512){
			na += 1024;
			s = realloc(s, na+1);
		}
		m = Bread(w->body, s+n, na-n);
		if(m <= 0)
			break;
		n += m;
	}
	s[n] = 0;
	winclosebody(w);
	*np = n;
	return s;
}

int
oreadblock(Ofile *f, int block, uint32_t off, char *buf, int nbuf)
{
	int n;

	if(block < 0 || block >= f->nblock) {
		werrstr("attempt to read %x/%lx\n", block, f->nblock);
		return -1;
	}

	if(off >= Blocksize){
		print("offset too far into block\n");
		return 0;
	}

	if(off+nbuf > Blocksize)
		nbuf = Blocksize-off;

	/* blocks start numbering at -1 [sic] */
	off += (block+1)*Blocksize;

	if(Bseek(f->b, off, 0) != off){
		print("seek failed\n");
		return -1;
	}

	n = Bread(f->b, buf, nbuf);
	if(n < 0)
		print("Bread failed: %r");
	return n;
}

static int
macholoadrel(MachoObj *m, MachoSect *sect)
{
	MachoRel *rel, *r;
	uchar *buf, *p;
	int i, n;
	uint32 v;
	
	if(sect->rel != nil || sect->nreloc == 0)
		return 0;
	rel = mal(sect->nreloc * sizeof r[0]);
	n = sect->nreloc * 8;
	buf = mal(n);
	if(Bseek(m->f, m->base + sect->reloff, 0) < 0 || Bread(m->f, buf, n) != n)
		return -1;
	for(i=0; i<sect->nreloc; i++) {
		r = &rel[i];
		p = buf+i*8;
		r->addr = m->e->e32(p);
		
		// TODO(rsc): Wrong interpretation for big-endian bitfields?
		if(r->addr & 0x80000000) {
			// scatterbrained relocation
			r->scattered = 1;
			v = r->addr >> 24;
			r->addr &= 0xFFFFFF;
			r->type = v & 0xF;
			v >>= 4;
			r->length = 1<<(v&3);
			v >>= 2;
			r->pcrel = v & 1;
			r->value = m->e->e32(p+4);
		} else {

static int
pswritepage(Document *d, int fd, int page)
{
	Biobuf *b = d->b;
	PSInfo *ps = d->extra;
	int t, n, i;
	long begin, end;
	char buf[8192];

	if(page == -1)
		begin = ps->psoff;
	else
		begin = ps->page[page].offset;

	end = ps->page[page+1].offset;

	if(chatty) {
		fprint(2, "writepage(%d)... from #%ld to #%ld...\n",
			page, begin, end);
	}
	Bseek(b, begin, 0);

	t = end-begin;
	n = sizeof(buf);
	if(n > t) n = t;
	while(t > 0 && (i=Bread(b, buf, n)) > 0) {
		if(write(fd, buf, i) != i)
			return -1;
		t -= i;
		if(n > t)
			n = t;
	}
	return end-begin;
}

int
wreadall(Win *w, char **sp)
{
	char *s;
	int m, na, n;

	if(w->body != nil)
		Bterm(w->body);
	openbody(w, OREAD);
	s = nil;
	na = 0;
	n = 0;
	for(;;){
		if(na < n+512){
			na += 1024;
			s = erealloc(s, na+1);
		}
		m = Bread(w->body, s+n, na-n);
		if(m <= 0)
			break;
		n += m;
	}
	s[n] = 0;
	Bterm(w->body);
	w->body = nil;
	*sp = s;
	return n;
}

Entry
getentry(long b)
{
	long e, n, dtop;
	static Entry ans;
	static int anslen = 0;

	e = (*dict->nextoff)(b+1);
	ans.doff = b;
	if(e < 0) {
		dtop = Bseek(bdict, 0L, 2);
		if(b < dtop) {
			e = dtop;
		} else {
			err("couldn't seek to entry");
			ans.start = 0;
			ans.end = 0;
		}
	}
	n = e-b;
	if(n) {
		if(n > anslen) {
			ans.start = realloc(ans.start, n);
			if(!ans.start) {
				err("out of memory");
				exits("nomem");
			}
			anslen = n;
		}
		Bseek(bdict, b, 0);
		n = Bread(bdict, ans.start, n);
		ans.end = ans.start + n;
	}
	return ans;
}

void texcache_setupmemcache(void)
{
    if (!glusememcache || texcache.memcache.noalloc || !texcache_enabled())
        return;

    texcache.memcache.size = Bfilelength(texcache.filehandle);

    if (texcache.memcache.size <= 0)
        return;

    texcache.memcache.ptr = (uint8_t *)Brealloc(texcache.memcache.ptr, texcache.memcache.size);

    if (!texcache.memcache.ptr)
    {
        initprintf("Failed allocating %d bytes for memcache, disabling memcache.\n", (int)texcache.memcache.size);
        texcache_clearmemcache();
        texcache.memcache.noalloc = 1;
        return;
    }

    if (Bread(texcache.filehandle, texcache.memcache.ptr, texcache.memcache.size) != (bssize_t)texcache.memcache.size)
    {
        initprintf("Failed reading texcache into memcache!\n");
        texcache_clearmemcache();
        texcache.memcache.noalloc = 1;
    }
}

int
gsopen(Modem *m)
{
	int n;
	char bytes[Gshdrsize];

	/*
	 *  Is this gs output
	 */
	n = Bread(m->bp, bytes, Gshdrsize);
	if(n != Gshdrsize)
		return seterror(m, Esys);
	if(bytes[0]!='\0' || strcmp(bytes+1, "PC Research, Inc")!=0){
		Bseek(m->bp, 0, 0);
		return seterror(m, Esys);
	}

	m->valid |= Vtype;
	if(bytes[0x1d])
		m->vr = 1;
	else
		m->vr = 0;
	m->wd = 0;
	m->ln = 2;
	m->df = 0;
	return Eok;
}

void texcache_syncmemcache(void)
{
    int32_t len = Bfilelength(texcache.filehandle);

    if (!texcache.memcache.ptr || texcache.filehandle == -1 || len <= (int32_t)texcache.memcache.size)
        return;

    texcache.memcache.ptr = (uint8_t *)Brealloc(texcache.memcache.ptr, len);

    if (!texcache.memcache.ptr)
    {
        texcache_clearmemcache();
        initprintf("Failed syncing memcache to texcache, disabling memcache.\n");
        texcache.memcache.noalloc = 1;
    }
    else
    {
        initprintf("Syncing memcache to texcache\n");
        Blseek(texcache.filehandle, texcache.memcache.size, BSEEK_SET);
        if (Bread(texcache.filehandle, texcache.memcache.ptr + texcache.memcache.size, len - texcache.memcache.size) != (bssize_t)(len-texcache.memcache.size))
        {
            initprintf("polymost_cachesync: Failed reading texcache into memcache!\n");
            texcache_clearmemcache();
            texcache.memcache.noalloc = 1;
        }
        else
        {
            texcache.memcache.size = len;
        }
    }
}

int
Bgetheader(Biobuf *b, Header *h)
{
	Icon *icon;
	int i;
	uint8_t buf[40];

	memset(h, 0, sizeof(*h));
	if(Bread(b, buf, 6) != 6)
		goto eof;
	if(gets(&buf[0]) != 0)
		goto header;
	if(gets(&buf[2]) != 1)
		goto header;
	h->n = gets(&buf[4]);

	for(i = 0; i < h->n; i++){
		icon = mallocz(sizeof(*icon), 1);
		if(icon == nil)
			sysfatal("malloc: %r");
		if(Bread(b, buf, 16) != 16)
			goto eof;
		icon->w = buf[0];
		icon->h = buf[1];
		icon->ncolor = buf[2] == 0 ? 256 : buf[2];
		if(buf[3] != 0)
			goto header;
		icon->nplane = gets(&buf[4]);
		icon->bits = gets(&buf[6]);
		icon->len = getl(&buf[8]);
		icon->offset = getl(&buf[12]);

		if(i == 0)
			h->first = icon;
		else
			h->last->next = icon;
		h->last = icon;
	}
	return 0;

eof:
	werrstr("unexpected EOF");
	return -1;
header:
	werrstr("unknown header format");
	return -1;
}

static Data*
readdata(Biobuf *b)
{
	Data *d;
	char str[32];
	int32_t len;

	if(Bread(b, str, 12) != 12)
		panic("can't read data hdr\n");

	len = atoi(str);
	d = emalloc(sizeof(*d) + len);
	if(Bread(b, d->data, len) != len)
		panic("can't read data body\n");
	d->len = len;
	return d;
}

void
loadstate(char *file)
{
	bp = Bopen(file, OREAD);
	if(bp == nil){
		message("open: %r");
		return;
	}
	Bread(bp, reg, sizeof(reg));
	Bread(bp, mem, sizeof(mem));
	Bread(bp, vram, sizeof(vram));
	Bread(bp, oam, sizeof(oam));
	Bread(bp, spcmem, sizeof(spcmem));
	Bread(bp, dsp, sizeof(dsp));
	get16s(cgram, nelem(cgram));
	ppuclock = get32();
	spcclock = get32();
	dspclock = get32();
	stimerclock = get32();
	rA = get16();
	rX = get16();
	rY = get16();
	rS = get16();
	rP = get8();
	rD = get16();
	rDB = get8()<<16;
	pc = get16();
	rPB = get8()<<16;
	emu = get8();
	irq = get8();
	nmi = get8();
	dma = get8();
	hdma = get32();
	wai = get8();
	mdr = get8();
	mdr1 = get8();
	mdr2 = get8();
	oamaddr = get16();
	vramlatch = get16();
	keylatch = get32();
	ppux = get16();
	ppuy = get16();
	htime = reg[0x4207] | reg[0x4208] << 8 & 0x100;
	vtime = reg[0x4209] | reg[0x420a] << 8 & 0x100;
	subcolor = get16();
	get16s(hofs, nelem(hofs));
	get16s(vofs, nelem(vofs));
	get16s((u16int*) m7, nelem(m7));
	sA = get8();
	sX = get8();
	sY = get8();
	sS = get8();
	sP = get8();
	dspstate = get8();
	dspcounter = get16();
	noise = get16();
	Bread(bp, spctimer, sizeof(spctimer));
	dspload();
	Bterm(bp);
}

char *
doread(Ram *r, int64_t off, int32_t cnt)
{
	int i, err;
	Block bs;
	ZipHead zh;
	static Qid oqid;
	static char buf[Maxbuf];
	static uint8_t *cache = nil;

	if (cnt > Maxbuf)
		sysfatal("file too big (>%d)", Maxbuf);

	if (Bseek(bin, r->addr & 0x7FFFFFFFFFFFFFFFLL, 0) < 0)
		sysfatal("seek failed");

	memset(&zh, 0, sizeof(zh));
	if (!header(bin, &zh))
		sysfatal("cannot get local header");

	switch(zh.meth){
	case 0:
		if (Bseek(bin, off, 1) < 0)
			sysfatal("seek failed");
		if (Bread(bin, buf, cnt) != cnt)
			sysfatal("read failed");
		break;
	case 8:
		if (r->qid.path != oqid.path){
			oqid = r->qid;
			if (cache)
				free(cache);
			cache = emalloc(r->ndata);

			bs.pos = cache;
			bs.limit = cache+r->ndata;
			if ((err = inflate(&bs, blwrite, bin, (int(*)(void*))Bgetc)) != FlateOk)
				sysfatal("inflate failed - %s", flateerr(err));

			if (blockcrc(crctab, crc, cache, r->ndata) != zh.crc)
				fprint(2, "%s - crc failed", r->name);

			if ((r->addr & High64) && MUNGE_CR){
				for (i = 0; i < r->ndata -1; i++)
					if (cache[i] == '\r' && cache[i +1] == '\n')
						cache[i] = ' ';
			}
		}
		memcpy(buf, cache+off, cnt);
		break;
	default:
		sysfatal("%d - unsupported compression method", zh.meth);
		break;
	}

	return buf;
}