void
setswapchan(Chan *c)
{
	uchar dirbuf[sizeof(Dir)+100];
	Dir d;
	int n;

	if(swapimage.c) {
		if(swapalloc.free != conf.nswap){
			cclose(c);
			error(Einuse);
		}
		cclose(swapimage.c);
	}

	/*
	 *  if this isn't a file, set the swap space
	 *  to be at most the size of the partition
	 */
	if(devtab[c->type]->dc != L'M'){
		n = devtab[c->type]->stat(c, dirbuf, sizeof dirbuf);
		if(n <= 0){
			cclose(c);
			error("stat failed in setswapchan");
		}
		convM2D(dirbuf, n, &d, nil);
		if(d.length < conf.nswap*BY2PG){
			conf.nswap = d.length/BY2PG;
			swapalloc.top = &swapalloc.swmap[conf.nswap];
			swapalloc.free = conf.nswap;
		}
	}

	swapimage.c = c;
}

long
sys_fstat(ulong *arg)
{
	Chan *c;
	char *name;
	uint l;
	uchar buf[128];	/* old DIRLEN plus a little should be plenty */
	char strs[128];
	Dir d;
	char old[] = "old fstat system call - recompile";

	validaddr(arg[1], 116, 1);
	c = fdtochan(arg[0], -1, 0, 1);
	if(waserror()){
		cclose(c);
		nexterror();
	}
	l = devtab[c->type]->stat(c, buf, sizeof buf);
	/* buf contains a new stat buf; convert to old. yuck. */
	if(l <= BIT16SZ)	/* buffer too small; time to face reality */
		error(old);
	name = pathlast(c->path);
	if(name)
		l = dirsetname(name, strlen(name), buf, l, sizeof buf);
	l = convM2D(buf, l, &d, strs);
	if(l == 0)
		error(old);
	packoldstat((uchar*)arg[1], &d);
	
	poperror();
	cclose(c);
	return 0;
}

static void
vbecall(Ureg *u)
{
	Proc *up = externup();
	Chan *creg, *cmem;
	uint32_t pa;

	cmem = namec("/dev/realmodemem", Aopen, ORDWR, 0);
	if(waserror()){
		cclose(cmem);
		nexterror();
	}
	creg = namec("/dev/realmode", Aopen, ORDWR, 0);
	if(waserror()){
		cclose(creg);
		nexterror();
	}
	pa = PADDR(RMBUF);
	cmem->dev->write(cmem, modebuf, sizeof modebuf, pa);
	u->trap = 0x10;
	print("vbecall: sizeof u is %d\n", sizeof *u);
	creg->dev->write(creg, u, sizeof *u, 0);

	creg->dev->read(creg, u, sizeof *u, 0);
	if((u->ax&0xFFFF) != 0x004F)
		error("vesa bios error");
	cmem->dev->read(cmem, modebuf, sizeof modebuf, pa);

	poperror();
	cclose(creg);
	poperror();
	cclose(cmem);
}

static long
dupread(Chan *c, void *va, long n, vlong offset)
{
	char *a = va;
	char buf[256];
	int fd, twicefd;

	if(c->qid.type == QTDIR)
		return devdirread(c, a, n, nil, 0, dupgen);
	twicefd = c->qid.path - 1;
	fd = twicefd/2;
	if(twicefd & 1){
		c = fdtochan(up->env->fgrp, fd, -1, 0, 1);
		if(waserror()){
			cclose(c);
			nexterror();
		}
		progfdprint(c, fd, 0, buf, sizeof buf);
		poperror();
		cclose(c);
		return readstr((ulong)offset, va, n, buf);
	}
	panic("dupread");
	return 0;
}

long
_syspipe(int fd[2])
{
	Chan *c[2];
	Dev *d;
	static char *datastr[] = {"data", "data1"};

	d = devtab[devno('|', 0)];
	c[0] = namec("#|", Atodir, 0, 0);
	c[1] = 0;
	fd[0] = -1;
	fd[1] = -1;

	if(waserror()){
		cclose(c[0]);
		if(c[1])
			cclose(c[1]);
		nexterror();
	}
	c[1] = cclone(c[0]);
	if(walk(&c[0], datastr+0, 1, 1, nil) < 0)
		error(Egreg);
	if(walk(&c[1], datastr+1, 1, 1, nil) < 0)
		error(Egreg);
	c[0] = d->open(c[0], ORDWR);
	c[1] = d->open(c[1], ORDWR);
	if(newfd2(fd, c) < 0)
		error(Enofd);
	poperror();

	return 0;
}

long
sysfversion(ulong *arg)
{
	char *vers;
	uint arglen, m, msize;
	Chan *c;

	msize = arg[1];
	vers = (char*)arg[2];
	arglen = arg[3];
	validaddr(arg[2], arglen, 1);
	/* check there's a NUL in the version string */
	if(arglen==0 || memchr(vers, 0, arglen)==0)
		error(Ebadarg);
	c = fdtochan(arg[0], ORDWR, 0, 1);
	if(waserror()){
		cclose(c);
		nexterror();
	}

	m = mntversion(c, vers, msize, arglen);

	cclose(c);
	poperror();
	return m;
}

int sysfversion(int fd, unsigned int msize, char *vers, unsigned int arglen)
{
	ERRSTACK(2);
	int m;
	struct chan *c;

	if (waserror()) {
		poperror();
		return -1;
	}

	/* check there's a NUL in the version string */
	if (arglen == 0 || memchr(vers, 0, arglen) == 0)
		error(EINVAL, ERROR_FIXME);

	c = fdtochan(&current->open_files, fd, O_RDWR, 0, 1);
	if (waserror()) {
		cclose(c);
		nexterror();
	}

	m = mntversion(c, vers, msize, arglen);

	poperror();
	cclose(c);

	poperror();
	return m;
}

/* must call with d qlocked */
static int
aoeidentify(Ctlr *d, SDunit *u)
{
	Chan *c;

	c = nil;
	if(waserror()){
		if(c)
			cclose(c);
		iprint("aoeidentify: %s\n", up->errstr);
		nexterror();
	}

	uprint("%s/ident", d->path);
	c = namec(up->genbuf, Aopen, OREAD, 0);
	devtab[c->type]->read(c, d->ident, sizeof d->ident, 0);

	poperror();
	cclose(c);

	d->feat = 0;
	d->smart = 0;
	identify(d, (ushort*)d->ident);

	memset(u->inquiry, 0, sizeof u->inquiry);
	u->inquiry[2] = 2;
	u->inquiry[3] = 2;
	u->inquiry[4] = sizeof u->inquiry - 4;
	memmove(u->inquiry+8, d->model, 40);

	return 0;
}

struct chan *fdtochan(struct fd_table *fdt, int fd, int mode, int chkmnt,
                      int iref)
{
	struct chan *c;

	c = lookup_fd(fdt, fd, iref, FALSE);
	if (!c) {
		/* We lost the info about why there was a problem (we used to track file
		 * group closed too, can add that in later). */
		error(EBADF, ERROR_FIXME);
	}
	if (chkmnt && (c->flag & CMSG)) {
		if (iref)
			cclose(c);
		error(EBADF, ERROR_FIXME);
	}
	if (mode < 0)
		return c;
	if ((mode & c->mode) != mode) {
		if (iref)
			cclose(c);
		error(EBADF,
		      "FD access mode failure: chan mode 0x%x, wanted 0x%x (opened with 0 instead of O_READ?)",
		      c->mode, mode);
	}
	return c;
}

static int32_t
wstat(Chan* c, uint8_t* p, usize n)
{
	Proc *up = externup();
	int32_t l;
	usize namelen;

	if(waserror()){
		cclose(c);
		nexterror();
	}

	/*
	 * Renaming mount points is disallowed to avoid surprises
	 * (which should be renamed? the mount point or the mounted Chan?).
	 */
	if(c->ismtpt){
		dirname(p, &namelen);
		if(namelen)
			nameerror(chanpath(c), Eismtpt);
	}
	l = c->dev->wstat(c, p, n);
	poperror();
	cclose(c);

	return l;
}

long
sysremove(ulong *arg)
{
	Chan *c;

	validaddr(arg[0], 1, 0);
	c = namec((char*)arg[0], Aremove, 0, 0);
	/*
	 * Removing mount points is disallowed to avoid surprises
	 * (which should be removed: the mount point or the mounted Chan?).
	 */
	if(c->ismtpt){
		cclose(c);
		error(Eismtpt);
	}
	if(waserror()){
		c->type = 0;	/* see below */
		cclose(c);
		nexterror();
	}
	devtab[c->type]->remove(c);
	/*
	 * Remove clunks the fid, but we need to recover the Chan
	 * so fake it up.  rootclose() is known to be a nop.
	 */
	c->type = 0;
	poperror();
	cclose(c);
	return 0;
}

void
sysfversion(Ar0* ar0, va_list list)
{
	Chan *c;
	char *version;
	int fd;
	u32int msize;
	usize nversion;

	/*
	 * int fversion(int fd, int bufsize, char *version, int nversion);
	 * should be
	 * usize fversion(int fd, u32int msize, char *version, usize nversion);
	 */
	fd = va_arg(list, int);
	msize = va_arg(list, u32int);
	version = va_arg(list, char*);
	nversion = va_arg(list, usize);
	version = validaddr(version, nversion, 1);
	/* check there's a NUL in the version string */
	if(nversion == 0 || memchr(version, 0, nversion) == nil)
		error(Ebadarg);

	c = fdtochan(fd, ORDWR, 0, 1);
	if(waserror()){
		cclose(c);
		nexterror();
	}

	ar0->u = mntversion(c, msize, version, nversion);

	cclose(c);
	poperror();
}

/* Could pass in the fdt instead of the proc, but we used to need the to_proc
 * for now so we can claim a VFS FD.  Careful, we don't close the old chan. */
int sys_dup_to(struct proc *from_proc, unsigned int from_fd,
               struct proc *to_proc, unsigned int to_fd)
{
	ERRSTACK(1);
	int ret;
	struct chan *c;

	if (waserror()) {
		poperror();
		return -1;
	}
	c = fdtochan(&from_proc->open_files, from_fd, -1, 0, 1);
	if (c->qid.type & QTAUTH) {
		cclose(c);
		error(EPERM, ERROR_FIXME);
	}
	ret = insert_obj_fdt(&to_proc->open_files, c, to_fd, 0, TRUE, FALSE);
	/* drop the ref from fdtochan.  if insert succeeded, there is one other ref
	 * stored in the FDT */
	cclose(c);
	if (ret < 0)
		error(EFAIL, "Can't insert FD %d into FDG", to_fd);
	poperror();
	return 0;
}

long
sysunmount(ulong *arg)
{
	Chan *cmount, *cmounted;

	cmounted = 0;

	validaddr(arg[1], 1, 0);
	cmount = namec((char *)arg[1], Amount, 0, 0);
	if(waserror()) {
		cclose(cmount);
		if(cmounted)
			cclose(cmounted);
		nexterror();
	}

	if(arg[0]) {
		/*
		 * This has to be namec(..., Aopen, ...) because
		 * if arg[0] is something like /srv/cs or /fd/0,
		 * opening it is the only way to get at the real
		 * Chan underneath.
		 */
		validaddr(arg[0], 1, 0);
		cmounted = namec((char*)arg[0], Aopen, OREAD, 0);
	}
	cunmount(cmount, cmounted);
	poperror();
	cclose(cmount);
	if(cmounted)
		cclose(cmounted);
	return 0;
}

uintptr
sysfversion(va_list list)
{
	uint msize, arglen;
	char *vers;
	Chan *c;
	int fd;

	fd = va_arg(list, int);
	msize = va_arg(list, uint);
	vers = va_arg(list, char*);
	arglen = va_arg(list, uint);
	validaddr((uintptr)vers, arglen, 1);
	/* check there's a NUL in the version string */
	if(arglen==0 || memchr(vers, 0, arglen)==0)
		error(Ebadarg);
	c = fdtochan(fd, ORDWR, 0, 1);
	if(waserror()){
		cclose(c);
		nexterror();
	}
	msize = mntversion(c, vers, msize, arglen);
	cclose(c);
	poperror();
	return msize;
}

long
sysstat(uint32 *arg)
{
	char *name;
	Chan *c;
	uint l;
	uchar *p;

	l = arg[2];
	p = uvalidaddr(arg[1], l, 1);
	name = uvalidaddr(arg[0], 1, 0);
	c = namec(name, Aaccess, 0, 0);
	if(waserror()){
		cclose(c);
		nexterror();
	}
	l = devtab[c->type]->stat(c, p, l);
	name = pathlast(c->path);
	if(name)
		l = dirsetname(name, strlen(name), p, l, arg[2]);

	poperror();
	cclose(c);
	return l;
}

long
sys_stat(uint32 *arg)
{
	Chan *c;
	uint l;
	uchar buf[128];	/* old DIRLEN plus a little should be plenty */
	char strs[128], *name, *elem;
	Dir d;
	char old[] = "old stat system call - recompile";
	uchar *p;

	p = uvalidaddr(arg[1], 116, 1);
	name = uvalidaddr(arg[0], 1, 0);
	c = namec(name, Aaccess, 0, 0);
	if(waserror()){
		cclose(c);
		nexterror();
	}
	l = devtab[c->type]->stat(c, buf, sizeof buf);
	/* buf contains a new stat buf; convert to old. yuck. */
	if(l <= BIT16SZ)	/* buffer too small; time to face reality */
		error(old);
	elem = pathlast(c->path);
	if(elem)
		l = dirsetname(elem, strlen(elem), buf, l, sizeof buf);
	l = convM2D(buf, l, &d, strs);
	if(l == 0)
		error(old);
	packoldstat(p, &d);
	
	poperror();
	cclose(c);
	return 0;
}

static vlong
_sysseek(int fd, vlong off, int whence)
{
	Chan *c;
	uchar buf[sizeof(Dir)+100];
	Dir dir;
	int n;

	c = fdtochan(fd, -1, 1, 1);
	if(waserror()){
		cclose(c);
		nexterror();
	}
	if(devtab[c->type]->dc == '|')
		error(Eisstream);

	switch(whence){
	case 0:
		if((c->qid.type & QTDIR) && off != 0)
			error(Eisdir);
		if(off < 0)
			error(Enegoff);
		c->offset = off;
		break;

	case 1:
		if(c->qid.type & QTDIR)
			error(Eisdir);
		lock(&c->ref.lk);	/* lock for read/write update */
		off = off + c->offset;
		if(off < 0)
			error(Enegoff);
		c->offset = off;
		unlock(&c->ref.lk);
		break;

	case 2:
		if(c->qid.type & QTDIR)
			error(Eisdir);
		n = devtab[c->type]->stat(c, buf, sizeof buf);
		if(convM2D(buf, n, &dir, nil) == 0)
			error("internal error: stat error in seek");
		off = dir.length + off;
		if(off < 0)
			error(Enegoff);
		c->offset = off;
		break;

	default:
		error(Ebadarg);
	}
	c->uri = 0;
	c->dri = 0;
	cclose(c);
	poperror();
	return off;
}

static int64_t
sseek(int fd, int64_t offset, int whence)
{
	Proc *up = externup();
	Chan *c;
	uint8_t buf[sizeof(Dir)+100];
	Dir dir;
	int n;

	c = fdtochan(fd, -1, 1, 1);
	if(waserror()){
		cclose(c);
		nexterror();
	}
	if(c->dev->dc == '|')
		error(Eisstream);

	switch(whence){
	case 0:
		if((c->qid.type & QTDIR) && offset != 0LL)
			error(Eisdir);
		c->offset = offset;
		break;

	case 1:
		if(c->qid.type & QTDIR)
			error(Eisdir);
		lock(&c->r.l);	/* lock for read/write update */
		offset += c->offset;
		c->offset = offset;
		unlock(&c->r.l);
		break;

	case 2:
		if(c->qid.type & QTDIR)
			error(Eisdir);
		n = c->dev->stat(c, buf, sizeof buf);
		if(convM2D(buf, n, &dir, nil) == 0)
			error("internal error: stat error in seek");
		offset += dir.length;
		c->offset = offset;
		break;

	default:
		error(Ebadarg);
	}
	c->uri = 0;
	c->dri = 0;
	cclose(c);
	poperror();

	return offset;
}

struct chan *fdtochan(struct fgrp *f, int fd, int mode, int chkmnt, int iref)
{
	
	struct chan *c;

	c = 0;

	spin_lock(&f->lock);
	if (f->closed) {
		spin_unlock(&f->lock);
		error("File group closed");
	}
	if (fd < 0 || f->maxfd < fd || (c = f->fd[fd]) == 0) {
		spin_unlock(&f->lock);
		set_errno(EBADF);
		error("Bad FD %d\n", fd);
	}
	if (iref)
		chan_incref(c);
	spin_unlock(&f->lock);

	if (chkmnt && (c->flag & CMSG)) {
		if (iref)
			cclose(c);
		error(Ebadusefd);
	}

	if (mode < 0 || c->mode == ORDWR) {
		return c;
	}

	if ((mode & OTRUNC) && IS_RDONLY(c->mode)) {
		if (iref)
			cclose(c);
		error(Ebadusefd);
	}

	/* TODO: this is probably wrong.  if you get this from a dev, in the dev's
	 * open, you are probably saving mode directly, without passing it through
	 * openmode. */
	if ((mode & ~OTRUNC) != c->mode) {
		warn("Trunc mode issue: mode %o, mode minus trunc %o, chan mode %o\n",
			 mode, mode & ~OTRUNC, c->mode);
		if (iref)
			cclose(c);
		error(Ebadusefd);
	}

	return c;
}