/*      $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);
        }
}