u9fs.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

		b |= QTDIR;

	/* no way to test append-only */
	/* no real way to test exclusive use, but mark devices as such */
	if(S_ISSPECIAL(st->st_mode))
		b |= QTEXCL;

	return b;
}

ulong
plan9mode(struct stat *st)
{
	return ((ulong)modebyte(st)<<24) | (st->st_mode & 0777);
}

/* 
 * this is for chmod, so don't worry about S_IFDIR
 */
mode_t
unixmode(Dir *d)
{
	return (mode_t)(d->mode&0777);
}

Qid
stat2qid(struct stat *st)
{
	uchar *p, *ep, *q;
	Qid qid;

	/*
	 * For now, ignore the device number.
	 */
	qid.path = 0;
	p = (uchar*)&qid.path;
	ep = p+sizeof(qid.path);
	q = p+sizeof(ino_t);
	if(q > ep){
		fprint(2, "warning: inode number too big\n");
		q = ep;
	}
	memmove(p, &st->st_ino, q-p);
	q = q+sizeof(dev_t);
	if(q > ep){
/*		fprint(2, "warning: inode number + device number too big %d+%d\n", sizeof(ino_t), sizeof(dev_t)); */
		q = ep - sizeof(dev_t);
		if(q < p)
			fprint(2, "warning: device number too big by itself\n");
		else
			*(dev_t*)q ^= st->st_dev;
	}

	qid.vers = st->st_mtime ^ (st->st_size << 8);
	qid.type = modebyte(st);
	return qid;
}

void
stat2dir(char *path, struct stat *st, Dir *d)
{
	User *u;
	char *q;

	memset(d, 0, sizeof(*d));
	d->qid = stat2qid(st);
	d->mode = plan9mode(st);
	d->atime = st->st_atime;
	d->mtime = st->st_mtime;
	d->length = st->st_size;

	d->uid = (u = uid2user(st->st_uid)) ? u->name : "???";
	d->gid = (u = gid2user(st->st_gid)) ? u->name : "???";
	d->muid = "";

	if((q = strrchr(path, '/')) != nil)
		d->name = q+1;
	else
		d->name = path;
}

void
rread(Fcall *rx, Fcall *tx)
{
	char *e, *path;
	uchar *p, *ep;
	int n;
	Fid *fid;
	Dir d;
	struct stat st;

	if(rx->count > msize-IOHDRSZ){
		seterror(tx, Etoolarge);
		return;
	}

	if((fid = oldfidex(rx->fid, -1, &e)) == nil){
		seterror(tx, e);
		return;
	}

	if (fid->auth) {
		char *e;
		e = auth->read(rx, tx);
		if (e)
			seterror(tx, e);
		return;
	}

	if(fid->omode == -1 || (fid->omode&3) == OWRITE){
		seterror(tx, Ebadusefid);
		return;
	}

	if(fid->dir){
		if(rx->offset != fid->diroffset){
			if(rx->offset != 0){
				seterror(tx, Ebadoffset);
				return;
			}
			rewinddir(fid->dir);
			fid->diroffset = 0;
		}

		p = (uchar*)tx->data;
		ep = (uchar*)tx->data+rx->count;
		for(;;){
			if(p+BIT16SZ >= ep)
				break;
			if(fid->dirent == nil)	/* one entry cache for when convD2M fails */
				if((fid->dirent = readdir(fid->dir)) == nil)
					break;
			if(strcmp(fid->dirent->d_name, ".") == 0
			|| strcmp(fid->dirent->d_name, "..") == 0){
				fid->dirent = nil;
				continue;
			}
			path = estrpath(fid->path, fid->dirent->d_name);
			memset(&st, 0, sizeof st);
			if(stat(path, &st) < 0){
				fprint(2, "dirread: stat(%s) failed: %s\n", path, strerror(errno));
				fid->dirent = nil;
				free(path);
				continue;
			}
			free(path);
			stat2dir(fid->dirent->d_name, &st, &d);
			if((n=(old9p ? convD2Mold : convD2M)(&d, p, ep-p)) <= BIT16SZ)
				break;
			p += n;
			fid->dirent = nil;
		}
		tx->count = p - (uchar*)tx->data;
		fid->diroffset += tx->count;
	}else{
		if((n = pread(fid->fd, tx->data, rx->count, rx->offset)) < 0){
			seterror(tx, strerror(errno));
			return;
		}
		tx->count = n;
	}
}

void
rwrite(Fcall *rx, Fcall *tx)
{
	char *e;
	Fid *fid;
	int n;

	if(rx->count > msize-IOHDRSZ){
		seterror(tx, Etoolarge);
		return;
	}

	if((fid = oldfidex(rx->fid, -1, &e)) == nil){
		seterror(tx, e);
		return;
	}

	if (fid->auth) {
		char *e;
		e = auth->write(rx, tx);
		if (e)
			seterror(tx, e);
		return;
	}

	if(fid->omode == -1 || (fid->omode&3) == OREAD || (fid->omode&3) == OEXEC){
		seterror(tx, Ebadusefid);
		return;
	}

	if((n = pwrite(fid->fd, rx->data, rx->count, rx->offset)) < 0){
		seterror(tx, strerror(errno));
		return;
	}
	tx->count = n;
}

void
rclunk(Fcall *rx, Fcall *tx)
{
	char *e;
	Fid *fid;

	if((fid = oldfidex(rx->fid, -1, &e)) == nil){
		seterror(tx, e);
		return;
	}
	if (fid->auth) {
		if (auth->clunk) {
			e = (*auth->clunk)(rx, tx);
			if (e) {
				seterror(tx, e);
				return;
			}
		}
	}
	else if(fid->omode != -1 && fid->omode&ORCLOSE)
		remove(fid->path);
	freefid(fid);
}

void
rremove(Fcall *rx, Fcall *tx)
{
	char *e;
	Fid *fid;

	if((fid = oldfid(rx->fid, &e)) == nil){
		seterror(tx, e);
		return;
	}
	if(userremove(fid, &e) < 0)
		seterror(tx, e);
	freefid(fid);
}

void
rstat(Fcall *rx, Fcall *tx)
{
	char *e;
	Fid *fid;
	Dir d;

	if((fid = oldfid(rx->fid, &e)) == nil){
		seterror(tx, e);
		return;
	}

	if(fidstat(fid, &e) < 0){
		seterror(tx, e);
		return;
	}

	stat2dir(fid->path, &fid->st, &d);
	if((tx->nstat=(old9p ? convD2Mold : convD2M)(&d, tx->stat, msize)) <= BIT16SZ)
		seterror(tx, "convD2M fails");
}

void
rwstat(Fcall *rx, Fcall *tx)
{
	char *e;
	char *p, *old, *new, *dir;
	gid_t gid;
	Dir d;
	Fid *fid;

	if((fid = oldfid(rx->fid, &e)) == nil){
		seterror(tx, e);
		return;
	}

	/*
	 * wstat is supposed to be atomic.
	 * we check all the things we can before trying anything.
	 * still, if we are told to truncate a file and rename it and only
	 * one works, we're screwed.  in such cases we leave things
	 * half broken and return an error.  it's hardly perfect.
	 */
	if((old9p ? convM2Dold : convM2D)(rx->stat, rx->nstat, &d, (char*)rx->stat) <= BIT16SZ){
		seterror(tx, Ewstatbuffer);
		return;
	}

	if(fidstat(fid, &e) < 0){
		seterror(tx, e);
		return;
	}

	/*
	 * The casting is necessary because d.mode is ulong and might,
	 * on some systems, be 64 bits.  We only want to compare the
	 * bottom 32 bits, since that's all that gets sent in the protocol.
	 * 
	 * Same situation for d.mtime and d.length (although that last check
	 * is admittedly superfluous, given the current lack of 128-bit machines).
	 */
	gid = (gid_t)-1;
	if(d.gid[0] != '\0'){
		User *g;

		g = gname2user(d.gid);
		if(g == nil){
			seterror(tx, Eunknowngroup);
			return;
		}
		gid = (gid_t)g->id;

		if(groupchange(fid->u, gid2user(gid), &e) < 0){
			seterror(tx, e);
			return;
		}		
	}

	if((u32int)d.mode != (u32int)~0 && (((d.mode&DMDIR)!=0) ^ (S_ISDIR(fid->st.st_mode)!=0))){
		seterror(tx, Edirchange);
		return;
	}

	if(strcmp(fid->path, "/") == 0){
		seterror(tx, "no wstat of root");
		return;
	}

	/*
	 * try things in increasing order of harm to the file.
	 * mtime should come after truncate so that if you
	 * do both the mtime actually takes effect, but i'd rather
	 * leave truncate until last.
	 * (see above comment about atomicity).
	 */
	if((u32int)d.mode != (u32int)~0 && chmod(fid->path, unixmode(&d)) < 0){
		if(chatty9p)
			fprint(2, "chmod(%s, 0%luo) failed\n", fid->path, unixmode(&d));
		seterror(tx, strerror(errno));
		return;
	}

	if((u32int)d.mtime != (u32int)~0){
		struct utimbuf t;

		t.actime = 0;
		t.modtime = d.mtime;
		if(utime(fid->path, &t) < 0){
			if(chatty9p)
				fprint(2, "utime(%s) failed\n", fid->path);
			seterror(tx, strerror(errno));
			return;
		}
	}

	if(gid != (gid_t)-1 && gid != fid->st.st_gid){
		if(chown(fid->path, (uid_t)-1, gid) < 0){
			if(chatty9p)
				fprint(2, "chgrp(%s, %d) failed\n", fid->path, gid);
			seterror(tx, strerror(errno));
			return;
		}
	}

	if(d.name[0]){
		old = fid->path;
		dir = estrdup(fid->path);
		if((p = strrchr(dir, '/')) > dir)
			*p = '\0';
		else{
			seterror(tx, "whoops: can't happen in u9fs");
			return;
		}
	
		new = estrpath(dir, d.name);
		if(strcmp(old, new) != 0 && rename(old, new) < 0){
			if(chatty9p)
				fprint(2, "rename(%s, %s) failed\n", old, new);
			seterror(tx, strerror(errno));
			free(new);
			free(dir);
			return;
		}
		fid->path = new;
		free(old);
		free(dir);
	}

	if((u64int)d.length != (u64int)~0 && truncate(fid->path, d.length) < 0){
		fprint(2, "truncate(%s, %lld) failed\n", fid->path, d.length);
		seterror(tx, strerror(errno));
		return;
	}
}

/*
 * we keep a table by numeric id.  by name lookups happen infrequently
 * while by-number lookups happen once for every directory entry read
 * and every stat request.
 */
User *utab[64];
User *gtab[64];

User*
adduser(struct passwd *p)
{
	User *u;

	u = emalloc(sizeof(*u));
	u->id = p->pw_uid;
	u->name = estrdup(p->pw_name);
	u->next = utab[p->pw_uid%nelem(utab)];
	u->defaultgid = p->pw_gid;
	utab[p->pw_uid%nelem(utab)] = u;
	return u;
}

int
useringroup(User *u, User *g)
{
	int i;

	for(i=0; i<g->nmem; i++)
		if(strcmp(g->mem[i], u->name) == 0)
			return 1;

	/*
	 * Hack around common Unix problem that everyone has
	 * default group "user" but /etc/group lists no members.
	 */
	if(u->defaultgid == g->id)
		return 1;
	return 0;
}

User*
addgroup(struct group *g)
{
	User *u;
	char **p;
	int n;

	u = emalloc(sizeof(*u));
	n = 0;
	for(p=g->gr_mem; *p; p++)
		n++;
	u->mem = emalloc(sizeof(u->mem[0])*n);
	n = 0;
	for(p=g->gr_mem; *p; p++)
		u->mem[n++] = estrdup(*p);
	u->nmem = n;
	u->id = g->gr_gid;
	u->name = estrdup(g->gr_name);
	u->next = gtab[g->gr_gid%nelem(gtab)];
	gtab[g->gr_gid%nelem(gtab)] = u;
	return u;
}

User*
uname2user(char *name)
{
	int i;
	User *u;
	struct passwd *p;

	for(i=0; i<nelem(utab); i++)
		for(u=utab[i]; u; u=u->next)
			if(strcmp(u->name, name) == 0)
				return u;

	if((p = getpwnam(name)) == nil)
		return nil;
	return adduser(p);
}

User*
uid2user(int id)
{
	User *u;
	struct passwd *p;

	for(u=utab[id%nelem(utab)]; u; u=u->next)
		if(u->id == id)
			return u;

	if((p = getpwuid(id)) == nil)
		return nil;
	return adduser(p);
}

User*
gname2user(char *name)
{
	int i;
	User *u;
	struct group *g;

	for(i=0; i<nelem(gtab); i++)
		for(u=gtab[i]; u; u=u->next)
			if(strcmp(u->name, name) == 0)
				return u;

	if((g = getgrnam(name)) == nil)
		return nil;
	return addgroup(g);
}

User*
gid2user(int id)
{
	User *u;
	struct group *g;

	for(u=gtab[id%nelem(gtab)]; u; u=u->next)
		if(u->id == id)
			return u;

	if((g = getgrgid(id)) == nil)
		return nil;
	return addgroup(g);
}

void
sysfatal(char *fmt, ...)
{
	char buf[1024];
	va_list va, temp;

	va_start(va, fmt);
	va_copy(temp, va);
	doprint(buf, buf+sizeof buf, fmt, &temp);
	va_end(temp);
	va_end(va);
	fprint(2, "u9fs: %s\n", buf);
	fprint(2, "last unix error: %s\n", strerror(errno));
	exit(1);
}

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

	if(n == 0)
		n = 1;
	p = malloc(n);
	if(p == 0)
		sysfatal("malloc(%ld) fails", (long)n);
	memset(p, 0, n);
	return p;
}

void*
erealloc(void *p, size_t n)
{
	if(p == 0)
		p = malloc(n);
	else
		p = realloc(p, n);
	if(p == 0)
		sysfatal("realloc(..., %ld) fails", (long)n);
	return p;
}

char*
estrdup(char *p)
{
	p = strdup(p);
	if(p == 0)