NetBSD/lib/librmt/rmtlib.c

/*	$NetBSD: rmtlib.c,v 1.29 2024/03/22 19:36:56 andvar Exp $	*/

/*
 *	rmt --- remote tape emulator subroutines
 *
 *	Originally written by Jeff Lee, modified some by Arnold Robbins
 *
 *	WARNING:  The man page rmt(8) for /etc/rmt documents the remote mag
 *	tape protocol which rdump and rrestore use.  Unfortunately, the man
 *	page is *WRONG*.  The author of the routines I'm including originally
 *	wrote his code just based on the man page, and it didn't work, so he
 *	went to the rdump source to figure out why.  The only thing he had to
 *	change was to check for the 'F' return code in addition to the 'E',
 *	and to separate the various arguments with \n instead of a space.  I
 *	personally don't think that this is much of a problem, but I wanted to
 *	point it out.
 *	-- Arnold Robbins
 *
 *	Redone as a library that can replace open, read, write, etc, by
 *	Fred Fish, with some additional work by Arnold Robbins.
 */

/*
 *	MAXUNIT --- Maximum number of remote tape file units
 *
 *	READ --- Return the number of the read side file descriptor
 *	WRITE --- Return the number of the write side file descriptor
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: rmtlib.c,v 1.29 2024/03/22 19:36:56 andvar Exp $");

#define RMTIOCTL	1
/* #define USE_REXEC	1 */	/* rexec code courtesy of Dan Kegel, srs!dan */

#include <sys/types.h>
#include <sys/stat.h>

#ifdef RMTIOCTL
#include <sys/ioctl.h>
#include <sys/mtio.h>
#endif

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <err.h>

#ifdef USE_REXEC
#include <netdb.h>
#endif

#define __RMTLIB_PRIVATE
#include <rmt.h>		/* get prototypes for remapped functions */

#include "pathnames.h"

static	int	_rmt_close(int);
static	int	_rmt_ioctl(int, unsigned long, void *);
static	off_t	_rmt_lseek(int, off_t, int);
static	int	_rmt_open(const char *, int, int);
static	ssize_t	_rmt_read(int, void *, size_t);
static	ssize_t	_rmt_write(int, const void *, size_t);
static	int	command(int, const char *);
static	int	remdev(const char *);
static	void	rmtabort(int);
static	int	status(int);


#define BUFMAGIC	64	/* a magic number for buffer sizes */
#define MAXUNIT		4

#define READ(fd)	(Ctp[fd][0])
#define WRITE(fd)	(Ptc[fd][1])

static int Ctp[MAXUNIT][2] = { {-1, -1}, {-1, -1}, {-1, -1}, {-1, -1} };
static int Ptc[MAXUNIT][2] = { {-1, -1}, {-1, -1}, {-1, -1}, {-1, -1} };


/*
 *	rmtabort --- close off a remote tape connection
 */
static void
rmtabort(int fildes)
{

	close(READ(fildes));
	close(WRITE(fildes));
	READ(fildes) = -1;
	WRITE(fildes) = -1;
}


/*
 *	command --- attempt to perform a remote tape command
 */
static int
command(int fildes, const char *buf)
{
	size_t blen;
	sig_t pstat;

	_DIAGASSERT(buf != NULL);

/*
 *	save current pipe status and try to make the request
 */

	blen = strlen(buf);
	pstat = signal(SIGPIPE, SIG_IGN);
	if ((size_t)write(WRITE(fildes), buf, blen) == blen) {
		signal(SIGPIPE, pstat);
		return 0;
	}

/*
 *	something went wrong. close down and go home
 */

	signal(SIGPIPE, pstat);
	rmtabort(fildes);

	errno = EIO;
	return -1;
}


/*
 *	status --- retrieve the status from the pipe
 */
static int
status(int fildes)
{
	int i;
	char c, *cp;
	char buffer[BUFMAGIC];

/*
 *	read the reply command line
 */

	for (i = 0, cp = buffer; i < BUFMAGIC; i++, cp++) {
		if (read(READ(fildes), cp, 1) != 1) {
			rmtabort(fildes);
			errno = EIO;
			return -1;
		}
		if (*cp == '\n') {
			*cp = 0;
			break;
		}
	}

	if (i == BUFMAGIC) {
		rmtabort(fildes);
		errno = EIO;
		return -1;
	}

/*
 *	check the return status
 */

	for (cp = buffer; *cp; cp++)
		if (*cp != ' ')
			break;

	if (*cp == 'E' || *cp == 'F') {
		errno = atoi(cp + 1);
		while (read(READ(fildes), &c, 1) == 1)
			if (c == '\n')
				break;

		if (*cp == 'F')
			rmtabort(fildes);

		return -1;
	}

/*
 *	check for mis-synced pipes
 */

	if (*cp != 'A') {
		rmtabort(fildes);
		errno = EIO;
		return -1;
	}

	return atoi(cp + 1);
}


#ifdef USE_REXEC
/*
 * _rmt_rexec
 *
 * execute /etc/rmt on a remote system using rexec().
 * Return file descriptor of bidirectional socket for stdin and stdout
 * If username is NULL, or an empty string, uses current username.
 *
 * ADR: By default, this code is not used, since it requires that
 * the user have a .netrc file in his/her home directory, or that the
 * application designer be willing to have rexec prompt for login and
 * password info. This may be unacceptable, and .rhosts files for use
 * with rsh are much more common on BSD systems.
 */

static	int	_rmt_rexec(const char *, const char *);

static int
_rmt_rexec(const char *host, const char *user)
{
	struct servent *rexecserv;

	_DIAGASSERT(host != NULL);
	/* user may be NULL */

	rexecserv = getservbyname("exec", "tcp");
	if (rexecserv == NULL)
		errx(1, "exec/tcp: service not available.");
	if ((user != NULL) && *user == '\0')
		user = NULL;
	return rexec(&host, rexecserv->s_port, user, NULL,
	    "/etc/rmt", NULL);
}
#endif /* USE_REXEC */


/*
 *	_rmt_open --- open a magtape device on system specified, as given user
 *
 *	file name has the form [user@]system:/dev/????
#ifdef COMPAT
 *	file name has the form system[.user]:/dev/????
#endif
 */

#define MAXHOSTLEN	257	/* BSD allows very long host names... */

static int
/*ARGSUSED*/
_rmt_open(const char *path, int oflag, int mode)
{
	int i;
	char buffer[2 * BUFMAGIC];
	char host[MAXHOSTLEN];
	char device[BUFMAGIC];
	char login[BUFMAGIC];
	char *sys, *dev, *user;
	const char *rshpath, *rsh;

	_DIAGASSERT(path != NULL);

	sys = host;
	dev = device;
	user = login;

/*
 *	first, find an open pair of file descriptors
 */

	for (i = 0; i < MAXUNIT; i++)
		if (READ(i) == -1 && WRITE(i) == -1)
			break;

	if (i == MAXUNIT) {
		errno = EMFILE;
		return -1;
	}

/*
 *	pull apart system and device, and optional user
 *	don't munge original string
 *	if COMPAT is defined, also handle old (4.2) style person.site notation.
 */

	while (*path != '@'
#ifdef COMPAT
			&& *path != '.'
#endif
			&& *path != ':') {
		*sys++ = *path++;
	}
	*sys = '\0';
	path++;

	if (*(path - 1) == '@') {
		(void)strlcpy(user, host, sizeof(login));
				/* saw user part of user@host */
		sys = host;			/* start over */
		while (*path != ':') {
			*sys++ = *path++;
		}
		*sys = '\0';
		path++;
	}
#ifdef COMPAT
	else if (*(path - 1) == '.') {
		while (*path != ':') {
			*user++ = *path++;
		}
		*user = '\0';
		path++;
	}
#endif
	else
		*user = '\0';

	while (*path) {
		*dev++ = *path++;
	}
	*dev = '\0';

#ifdef USE_REXEC
/*
 *	Execute the remote command using rexec
 */
	READ(i) = WRITE(i) = _rmt_rexec(host, login);
	if (READ(i) < 0)
		return -1;
#else
/*
 *	setup the pipes for the 'rsh' command and fork
 */

	if (pipe(Ptc[i]) == -1 || pipe(Ctp[i]) == -1)
		return -1;

	switch (fork()) {
	case -1:
		return -1;

	case 0:
		close(0);
		dup(Ptc[i][0]);
		close(Ptc[i][0]); close(Ptc[i][1]);
		close(1);
		dup(Ctp[i][1]);
		close(Ctp[i][0]); close(Ctp[i][1]);
		(void) setuid(getuid());
		(void) setgid(getgid());

		if ((rshpath = getenv("RCMD_CMD")) == NULL)
			rshpath = _PATH_RSH;
		if ((rsh = strrchr(rshpath, '/')) == NULL)
			rsh = rshpath;
		else
			rsh++;

		if (*login) {
			execl(rshpath, rsh, host, "-l", login, _PATH_RMT, NULL);
		} else {
			execl(rshpath, rsh, host, _PATH_RMT, NULL);
		}

/*
 *	bad problems if we get here
 */

		err(1, "Cannot exec %s", rshpath);
		/*FALLTHROUGH*/
	default:
		break;
	}

	close(Ptc[i][0]); close(Ctp[i][1]);
#endif

/*
 *	now attempt to open the tape device
 */

	(void)snprintf(buffer, sizeof(buffer), "O%s\n%d\n", device, oflag);
	if (command(i, buffer) == -1 || status(i) == -1)
		return -1;

	return i;
}


/*
 *	_rmt_close --- close a remote magtape unit and shut down
 */
static int
_rmt_close(int fildes)
{
	int rc;

	if (command(fildes, "C\n") != -1) {
		rc = status(fildes);

		rmtabort(fildes);
		return rc;
	}

	return -1;
}


/*
 *	_rmt_read --- read a buffer from a remote tape
 */
static ssize_t
_rmt_read(int fildes, void *buf, size_t nbyte)
{
	size_t rc;
	int rv;
	ssize_t nread;
	char *p;
	char buffer[BUFMAGIC];

	_DIAGASSERT(buf != NULL);

	(void)snprintf(buffer, sizeof buffer, "R%zu\n", nbyte);
	if (command(fildes, buffer) == -1 || (rv = status(fildes)) == -1)
		return -1;

	if (rv > (int)nbyte)
		rv = (int)nbyte;

	for (rc = rv, p = buf; rc > 0; rc -= nread, p += nread) {
		if ((nread = read(READ(fildes), p, rc)) <= 0) {
			rmtabort(fildes);
			errno = EIO;
			return -1;
		}
	}

	return rv;
}


/*
 *	_rmt_write --- write a buffer to the remote tape
 */
static ssize_t
_rmt_write(int fildes, const void *buf, size_t nbyte)
{
	char buffer[BUFMAGIC];
	sig_t pstat;

	_DIAGASSERT(buf != NULL);

	(void)snprintf(buffer, sizeof buffer, "W%zu\n", nbyte);
	if (command(fildes, buffer) == -1)
		return -1;

	pstat = signal(SIGPIPE, SIG_IGN);
	if ((size_t)write(WRITE(fildes), buf, nbyte) == nbyte) {
		signal(SIGPIPE, pstat);
		return status(fildes);
	}

	signal(SIGPIPE, pstat);
	rmtabort(fildes);
	errno = EIO;
	return -1;
}


/*
 *	_rmt_lseek --- perform an imitation lseek operation remotely
 */
static off_t
_rmt_lseek(int fildes, off_t offset, int whence)
{
	char buffer[BUFMAGIC];

	/*LONGLONG*/
	(void)snprintf(buffer, sizeof buffer, "L%lld\n%d\n", (long long)offset,
	    whence);
	if (command(fildes, buffer) == -1)
		return -1;

	return status(fildes);
}


/*
 *	_rmt_ioctl --- perform raw tape operations remotely
 */
#ifdef RMTIOCTL
static int
_rmt_ioctl(int fildes, unsigned long op, void *arg)
{
	char c;
	int rv;
	size_t rc;
	ssize_t cnt;
	char buffer[BUFMAGIC], *p;
	struct mtop *mtop = arg;

	_DIAGASSERT(arg != NULL);

/*
 *	MTIOCOP is the easy one. nothing is transferred in binary
 */

	if (op == MTIOCTOP) {
		(void)snprintf(buffer, sizeof buffer, "I%d\n%d\n",
		    mtop->mt_op, mtop->mt_count);
		if (command(fildes, buffer) == -1)
			return -1;
		return status(fildes);
	}

/*
 *	we can only handle 2 ops, if not the other one, punt
 */

	if (op != MTIOCGET) {
		errno = EINVAL;
		return -1;
	}

/*
 *	grab the status and read it directly into the structure
 *	this assumes that the status buffer is (hopefully) not
 *	padded and that 2 shorts fit in a long without any word
 *	alignment problems, ie - the whole struct is contiguous
 *	NOTE - this is probably NOT a good assumption.
 */

	if (command(fildes, "S") == -1 || (rv = status(fildes)) == -1)
		return -1;

	memset(arg, 0, sizeof(struct mtget));
	for (rc = rv, p = arg; rc > 0; rc -= cnt, p += cnt) {
		if ((cnt = read(READ(fildes), p, rc)) <= 0) {
			rmtabort(fildes);
			errno = EIO;
			return -1;
		}
	}

/*
 *	now we check for byte position. mt_type is a small integer field
 *	(normally) so we will check its magnitude. if it is larger than
 *	256, we will assume that the bytes are swapped and go through
 *	and reverse all the bytes
 */

	if (((struct mtget *)(void *)p)->mt_type < 256)
		return 0;

	for (cnt = 0; cnt < rv; cnt += 2) {
		c = p[cnt];
		p[cnt] = p[cnt + 1];
		p[cnt + 1] = c;
	}

	return 0;
}
#endif /* RMTIOCTL */


/*
 *	Added routines to replace open(), close(), lseek(), ioctl(), etc.
 *	The preprocessor can be used to remap these the rmtopen(), etc
 *	thus minimizing source changes:
 *
 *		#ifdef <something>
 *		#  define access rmtaccess
 *		#  define close rmtclose
 *		#  define creat rmtcreat
 *		#  define dup rmtdup
 *		#  define fcntl rmtfcntl
 *		#  define fstat rmtfstat
 *		#  define ioctl rmtioctl
 *		#  define isatty rmtisatty
 *		#  define lseek rmtlseek
 *		#  define lstat rmtlstat
 *		#  define open rmtopen
 *		#  define read rmtread
 *		#  define stat rmtstat
 *		#  define write rmtwrite
 *		#endif
 *
 *	-- Fred Fish
 *
 *	ADR --- I set up a <rmt.h> include file for this
 *
 */

/*
 *	Note that local vs remote file descriptors are distinquished
 *	by adding a bias to the remote descriptors.  This is a quick
 *	and dirty trick that may not be portable to some systems.
 */

#define REM_BIAS 128


/*
 *	Test pathname to see if it is local or remote.  A remote device
 *	is any string that contains ":/dev/".  Returns 1 if remote,
 *	0 otherwise.
 */

static int
remdev(const char *path)
{

	_DIAGASSERT(path != NULL);

	if ((path = strchr(path, ':')) != NULL) {
		if (strncmp(path + 1, "/dev/", 5) == 0) {
			return 1;
		}
	}
	return 0;
}


/*
 *	Open a local or remote file.  Looks just like open(2) to
 *	caller.
 */
int
rmtopen(const char *path, int oflag, ...)
{
	mode_t mode;
	int fd;
	va_list ap;
	va_start(ap, oflag);

	mode = va_arg(ap, mode_t);
	va_end(ap);

	_DIAGASSERT(path != NULL);

	if (remdev(path)) {
		fd = _rmt_open(path, oflag, (int)mode);

		return (fd == -1) ? -1 : (fd + REM_BIAS);
	} else {
		return open(path, oflag, mode);
	}
}

/*
 *	Test pathname for specified access.  Looks just like access(2)
 *	to caller.
 */

int
rmtaccess(const char *path, int amode)
{

	_DIAGASSERT(path != NULL);

	if (remdev(path)) {
		return 0;		/* Let /etc/rmt find out */
	} else {
		return access(path, amode);
	}
}


/*
 *	Isrmt. Let a programmer know he has a remote device.
 */
int
isrmt(int fd)
{
	int unbias = fd - REM_BIAS;

	return (fd >= REM_BIAS) && unbias < MAXUNIT &&
	    (WRITE(unbias) != -1 || READ(unbias) != -1);
}


/*
 *	Read from stream.  Looks just like read(2) to caller.
 */
ssize_t
rmtread(int fildes, void *buf, size_t nbyte)
{

	_DIAGASSERT(buf != NULL);

	if (isrmt(fildes)) {
		return _rmt_read(fildes - REM_BIAS, buf, nbyte);
	} else {
		return read(fildes, buf, nbyte);
	}
}


/*
 *	Write to stream.  Looks just like write(2) to caller.
 */
ssize_t
rmtwrite(int fildes, const void *buf, size_t nbyte)
{

	_DIAGASSERT(buf != NULL);

	if (isrmt(fildes)) {
		return _rmt_write(fildes - REM_BIAS, buf, nbyte);
	} else {
		return write(fildes, buf, nbyte);
	}
}

/*
 *	Perform lseek on file.  Looks just like lseek(2) to caller.
 */
off_t
rmtlseek(int fildes, off_t offset, int whence)
{

	if (isrmt(fildes)) {
		return _rmt_lseek(fildes - REM_BIAS, offset, whence);
	} else {
		return lseek(fildes, offset, whence);
	}
}


/*
 *	Close a file.  Looks just like close(2) to caller.
 */
int
rmtclose(int fildes)
{

	if (isrmt(fildes)) {
		return _rmt_close(fildes - REM_BIAS);
	} else {
		return close(fildes);
	}
}


/*
 *	Do ioctl on file.  Looks just like ioctl(2) to caller.
 */
int
rmtioctl(int fildes, unsigned long request, ...)
{
	void *arg;
	va_list ap;
	va_start(ap, request);

	arg = va_arg(ap, void *);
	va_end(ap);

	/* XXX: arg may be NULL ? */

	if (isrmt(fildes)) {
#ifdef RMTIOCTL
		return _rmt_ioctl(fildes - REM_BIAS, request, arg);
#else
		errno = EOPNOTSUPP;
		return -1;		/* For now (fnf) */
#endif
	} else {
		return ioctl(fildes, request, arg);
	}
}


/*
 *	Duplicate an open file descriptor.  Looks just like dup(2)
 *	to caller.
 */
int
rmtdup(int fildes)
{

	if (isrmt(fildes)) {
		errno = EOPNOTSUPP;
		return -1;		/* For now (fnf) */
	} else {
		return dup(fildes);
	}
}


/*
 *	Get file status.  Looks just like fstat(2) to caller.
 */
int
rmtfstat(int fildes, struct stat *buf)
{

	_DIAGASSERT(buf != NULL);

	if (isrmt(fildes)) {
		errno = EOPNOTSUPP;
		return -1;		/* For now (fnf) */
	} else {
		return fstat(fildes, buf);
	}
}


/*
 *	Get file status.  Looks just like stat(2) to caller.
 */
int
rmtstat(const char *path, struct stat *buf)
{

	_DIAGASSERT(path != NULL);
	_DIAGASSERT(buf != NULL);

	if (remdev(path)) {
		errno = EOPNOTSUPP;
		return -1;		/* For now (fnf) */
	} else {
		return stat(path, buf);
	}
}


/*
 *	Create a file from scratch.  Looks just like creat(2) to the caller.
 */
int
rmtcreat(const char *path, mode_t mode)
{

	_DIAGASSERT(path != NULL);

	if (remdev(path)) {
		return rmtopen(path, O_WRONLY | O_CREAT, mode);
	} else {
		return open(path, O_CREAT | O_TRUNC | O_WRONLY, mode);
	}
}


/*
 *	Rmtfcntl. Do a remote fcntl operation.
 */
int
rmtfcntl(int fd, int cmd, ...)
{
	void *arg;
	va_list ap;
	va_start(ap, cmd);

	arg = va_arg(ap, void *);
	va_end(ap);

	/* XXX: arg may be NULL ? */

	if (isrmt(fd)) {
		errno = EOPNOTSUPP;
		return -1;
	} else {
		return fcntl(fd, cmd, arg);
	}
}


/*
 *	Rmtisatty.  Do the isatty function.
 */
int
rmtisatty(int fd)
{

	if (isrmt(fd))
		return 0;
	else
		return isatty(fd);
}


/*
 *	Get file status, even if symlink.  Looks just like lstat(2) to caller.
 */
int
rmtlstat(const char *path, struct stat *buf)
{

	_DIAGASSERT(path != NULL);
	_DIAGASSERT(buf != NULL);

	if (remdev(path)) {
		errno = EOPNOTSUPP;
		return -1;		/* For now (fnf) */
	} else {
		return lstat(path, buf);
	}
}