* rmt --- remote tape emulator subroutines

/* $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);
}
}