自学教程：C++ Bread函数代码示例

voidstatsinit(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;}

intoreadblock(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 intmacholoadrel(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 intpswritepage(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;}

intwreadall(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;}

Entrygetentry(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;    }}

intgsopen(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;        }    }}

intBgetheader(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;}

voidloadstate(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;}

voidvncrdbytes(Vnc *v, void *a, int n){	if(Bread(&v->in, a, n) != n){		if(verbose > 1)			fprint(2, "hungup while reading/n");		vnchungup(v);	}}

intBgetint(Biobuf *b){	uchar p[4];	if(Bread(b, p, 4) != 4)		sysfatal("short read");	return (p[0]<<24)|(p[1]<<16)|(p[2]<<8)|p[3];}

uchar*getrange(Block *b){	uchar *data;	char *status;	int netfd;	static Biobuf netbio;	b->len = Blocksize;	if(b->off + b->len > size)		b->len = size - b->off;	if(debug)		print("getrange: %lld %lld/n", b->off, b->len);	netfd = dialhttp(&netbio);	fprint(netfd, 		"GET %s HTTP/1.1/r/n"		"Host: %s/r/n"		"Accept-Encoding:/r/n"		"Range: bytes=%lld-%lld/r/n"		"/r/n",		get, host, b->off, b->off+b->len);	Bflush(&netbio);	status = readhttphdr(&netbio, nil);	if(status == nil)		return nil;	/*	 * Some servers (e.g., www.google.com) return 200 OK	 * when you ask for the entire page in one range.	 */	if(strstr(status, "206 Partial Content")==nil	&& (b->off!=0 || b->len!=size || strstr(status, "200 OK")==nil)){		free(status);		close(netfd);		werrstr("did not get requested range");		return nil;	}	free(status);	data = emalloc9p(b->len);	if(Bread(&netbio, data, b->len) != b->len){		free(data);		close(netfd);		werrstr("not enough bytes read");		return nil;	}	b->p = data;	close(netfd);	return data;}

void devread(void){	long offset, sector = bnum;	int dosdev = (int) inode.i_dev;	for (offset = 0; offset < cnt; offset += BPS)	{		Bread(dosdev, badsect(dosdev, sector++));		bcopy(I_ADDR, iodest+offset, BPS);	}}

/* * * * * * utility * * * * * */static intBgbit32(Biobuf *b, u32int *p){	uchar tmp[4];	if(Bread(b, tmp, 4) != 4)		return -1;	*p = gbit32(tmp);	return 0;}

char*qmail(char **argv, char *buf, int n, Biobuf *cout){    Waitmsg *status;    int i, pid, pipefd[2];    char path[512];    Biobuf *bp;    pid = 0;    if(tflag == 0) {        if(pipe(pipefd) < 0)            exits("pipe");        pid = fork();        if(pid == 0) {            dup(pipefd[0], 0);            for(i = sysfiles(); i >= 3; i--)                close(i);            snprint(path, sizeof(path), "%s/qer", UPASBIN);            *argv=path;            exec(path, argv);            exits("exec");        }        Binit(&bout, pipefd[1], OWRITE);        bp = &bout;    } else        bp = Bopen("/dev/null", OWRITE);    while(n > 0) {        Bwrite(bp, buf, n);        if(cout)            Bwrite(cout, buf, n);        n = Bread(&bin, buf, sizeof(buf)-1);    }    Bterm(bp);    if(cout)        Bterm(cout);    if(tflag)        return 0;    close(pipefd[1]);    close(pipefd[0]);    for(;;) {        status = wait();        if(status == nil || status->pid == pid)            break;        free(status);    }    if(status == nil)        strcpy(buf, "wait failed");    else {        strcpy(buf, status->msg);        free(status);    }    return buf;}

/* * * * * * logging * * * * * */static intapplylog(XDStore *ds){	int np;	uchar *a, *buf;	u32int addr;	Biobuf *b;	Dpage *p;	buf = malloc(ds->ds.pagesize);	if(buf == nil)		return -1;	b = malloc(sizeof(Biobuf));	if(b == nil)		goto Error;	if(seek(ds->logfd, 0, 0) != 0){	Error:		free(buf);		free(b);		return -1;	}	Binit(b, ds->logfd, OREAD);	if(Bgbit32(b, &addr) < 0)		goto Error;	if(addr != gbit32((uchar*)"log/n")){		werrstr("malformed log");		goto Error;	}	np = 0;	for(;;){		if(Bgbit32(b, &addr) < 0)			goto Error;		if(addr == ~(u32int)0)			break;DBG print("apply log page %ud/n", addr);		p = findpage(ds, addr);		if(p)			a = p->a;		else			a = buf;		if(Bread(b, a, ds->ds.pagesize) != ds->ds.pagesize)			goto Error;		if(pwrite(ds->fd, a, ds->ds.pagesize, addr) != ds->ds.pagesize){abort();			goto Error;}		np++;	}	fprint(2, "applied changes to %d pages/n", np);	free(b);	free(buf);	return 0 && fsync(ds->fd);}

intisar(Biobuf *bp){	int n;	char magbuf[SARMAG];	n = Bread(bp, magbuf, SARMAG);	if(n == SARMAG && strncmp(magbuf, ARMAG, SARMAG) == 0)		return 1;	return 0;}

voidCreadblock(Cdimg *cd, void *buf, ulong block, ulong len){	assert(block != 0);	/* nothing useful there */	Bflush(&cd->bwr);	if(Bseek(&cd->brd, block*Blocksize, 0) != block*Blocksize)		sysfatal("error seeking to block %lud", block);	if(Bread(&cd->brd, buf, len) != len)		sysfatal("error reading %lud bytes at block %lud: %r %lld", len, block, Bseek(&cd->brd, 0, 2));}

static intisobjfile(char *f){	int n, v;	Biobuf *b;	char buf1[5], buf2[SARMAG];	b = Bopen(f, OREAD);	if(b == nil)		return 0;	n = Bread(b, buf1, 5);	if(n == 5 && (buf1[2] == 1 && buf1[3] == '<' || buf1[3] == 1 && buf1[4] == '<'))		v = 1;	/* good enough for our purposes */	else{		Bseek(b, 0, 0);		n = Bread(b, buf2, SARMAG);		v = n == SARMAG && strncmp(buf2, ARMAG, SARMAG) == 0;	}	Bterm(b);	return v;}

/* read ahead a byte.  so we must check peek here */staticintreadbyte(Header *h){	uchar x;	if(h->peek >= 0){		x = h->peek;		h->peek = -1;	}else if(Bread(h->fd, &x, 1) != 1)		jpgerror(h, readerr);	return x;}

voidarread(Biobuf *b, Armember *bp, int n)	/* read an image into a member buffer */{    int i;    bp->member = armalloc(n);    i = Bread(b, bp->member, n);    if (i < 0) {        free(bp->member);        bp->member = 0;        rderr();    }}

Proc*readsnap(Biobuf *b){	char *q;	char buf[12];	int32_t pid;	Proc *p, *plist;	int i, n;	if((q = Brdline(b, '/n')) == nil)		panic("error reading snapshot file");	if(strncmp(q, "process snapshot", strlen("process snapshot")) != 0)		panic("bad snapshot file format");	plist = nil;	while(q = Brdline(b, '/n')) {		q[Blinelen(b)-1] = 0;		pid = atol(q);		q += 12;		p = findpid(plist, pid);		if(p == nil) {			p = emalloc(sizeof(*p));			p->link = plist;			p->pid = pid;			plist = p;		}		for(i=0; i<Npfile; i++) {			if(strcmp(pfile[i], q) == 0) {				p->d[i] = readdata(b);				break;			}		}		if(i != Npfile)			continue;		if(strcmp(q, "mem") == 0) {			if(Bread(b, buf, 12) != 12) 				panic("can't read memory section");			n = atoi(buf);			p->nseg = n;			p->seg = emalloc(n*sizeof(*p->seg));			for(i=0; i<n; i++)				readseg(&p->seg[i], b, plist);		} else if(strcmp(q, "text") == 0)			readseg(&p->text, b, plist);		else			panic("unknown section");	}	return plist;}

void loadwadheader(void){    int i, j;    Bread(fil1,&tempbuf[0],12);    numwads = ((int)tempbuf[4])+(((int)tempbuf[5])<<8)+(((int)tempbuf[6])<<16)+(((int)tempbuf[7])<<24);    i = ((int)tempbuf[8])+(((int)tempbuf[9])<<8)+(((int)tempbuf[10])<<16)+(((int)tempbuf[11])<<24);    Blseek(fil1,i,BSEEK_SET);    Bread(fil1,&tempbuf[0],numwads*16);    j = 0;    for(i=0;i<numwads;i++)    {        wadplc[i] = ((int)tempbuf[j])+(((int)tempbuf[j+1])<<8)+(((int)tempbuf[j+2])<<16)+(((int)tempbuf[j+3])<<24);        j += 4;        wadlen[i] = ((int)tempbuf[j])+(((int)tempbuf[j+1])<<8)+(((int)tempbuf[j+2])<<16)+(((int)tempbuf[j+3])<<24);        j += 4;        wadata[i][0] = tempbuf[j+0]; wadata[i][1] = tempbuf[j+1];        wadata[i][2] = tempbuf[j+2]; wadata[i][3] = tempbuf[j+3];        wadata[i][4] = tempbuf[j+4]; wadata[i][5] = tempbuf[j+5];        wadata[i][6] = tempbuf[j+6]; wadata[i][7] = tempbuf[j+7];        j += 8;    }}

/* * Be aware that cnt is rounded up to N*BPS */voiddevread(char *iodest, int sector, int cnt){	int offset;	char *p;	int dosdev_copy;	for (offset = 0; offset < cnt; offset += BPS)	{		dosdev_copy = dosdev;		p = Bread(dosdev_copy, badsect(sector++));		bcopy(p, iodest+offset, BPS);	}}