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file_subs.c

/*    $OpenBSD: file_subs.c,v 1.30 2005/11/09 19:59:06 otto Exp $ */
/*    $NetBSD: file_subs.c,v 1.4 1995/03/21 09:07:18 cgd Exp $    */

/*-
 * Copyright (c) 1992 Keith Muller.
 * Copyright (c) 1992, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Keith Muller of the University of California, San Diego.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#ifndef lint
#if 0
static const char sccsid[] = "@(#)file_subs.c   8.1 (Berkeley) 5/31/93";
#else
static const char rcsid[] = "$OpenBSD: file_subs.c,v 1.30 2005/11/09 19:59:06 otto Exp $";
#endif
#endif /* not lint */

#include <sys/param.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <sys/uio.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "pax.h"
#include "options.h"
#include "extern.h"

static int
mk_link(char *, struct stat *, char *, int);

/*
 * routines that deal with file operations such as: creating, removing;
 * and setting access modes, uid/gid and times of files
 */

#define FILEBITS        (S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
#define SETBITS               (S_ISUID | S_ISGID)
#define ABITS                 (FILEBITS | SETBITS)

/*
 * file_creat()
 *    Create and open a file.
 * Return:
 *    file descriptor or -1 for failure
 */

int
file_creat(ARCHD *arcn)
{
      int fd = -1;
      mode_t file_mode;
      int oerrno;

      /*
       * Assume file doesn't exist, so just try to create it, most times this
       * works. We have to take special handling when the file does exist. To
       * detect this, we use O_EXCL. For example when trying to create a
       * file and a character device or fifo exists with the same name, we
       * can accidently open the device by mistake (or block waiting to open).
       * If we find that the open has failed, then spend the effort to
       * figure out why. This strategy was found to have better average
       * performance in common use than checking the file (and the path)
       * first with lstat.
       */
      file_mode = arcn->sb.st_mode & FILEBITS;
      if ((fd = open(arcn->name, O_WRONLY | O_CREAT | O_TRUNC | O_EXCL,
          file_mode)) >= 0)
            return(fd);

      /*
       * the file seems to exist. First we try to get rid of it (found to be
       * the second most common failure when traced). If this fails, only
       * then we go to the expense to check and create the path to the file
       */
      if (unlnk_exist(arcn->name, arcn->type) != 0)
            return(-1);

      for (;;) {
            /*
             * try to open it again, if this fails, check all the nodes in
             * the path and give it a final try. if chk_path() finds that
             * it cannot fix anything, we will skip the last attempt
             */
            if ((fd = open(arcn->name, O_WRONLY | O_CREAT | O_TRUNC,
                file_mode)) >= 0)
                  break;
            oerrno = errno;
            if (nodirs || chk_path(arcn->name,arcn->sb.st_uid,arcn->sb.st_gid) < 0) {
                  syswarn(1, oerrno, "Unable to create %s", arcn->name);
                  return(-1);
            }
      }
      return(fd);
}

/*
 * file_close()
 *    Close file descriptor to a file just created by pax. Sets modes,
 *    ownership and times as required.
 * Return:
 *    0 for success, -1 for failure
 */

void
file_close(ARCHD *arcn, int fd)
{
      int res = 0;

      if (fd < 0)
            return;

      /*
       * set owner/groups first as this may strip off mode bits we want
       * then set file permission modes. Then set file access and
       * modification times.
       */
      if (pids)
            res = fset_ids(arcn->name, fd, arcn->sb.st_uid,
                arcn->sb.st_gid);

      /*
       * IMPORTANT SECURITY NOTE:
       * if not preserving mode or we cannot set uid/gid, then PROHIBIT
       * set uid/gid bits
       */
      if (!pmode || res)
            arcn->sb.st_mode &= ~(SETBITS);
      if (pmode)
            fset_pmode(arcn->name, fd, arcn->sb.st_mode);
      if (patime || pmtime)
            fset_ftime(arcn->name, fd, arcn->sb.st_mtime,
                arcn->sb.st_atime, 0);
      if (close(fd) < 0)
            syswarn(0, errno, "Unable to close file descriptor on %s",
                arcn->name);
}

/*
 * lnk_creat()
 *    Create a hard link to arcn->ln_name from arcn->name. arcn->ln_name
 *    must exist;
 * Return:
 *    0 if ok, -1 otherwise
 */

int
lnk_creat(ARCHD *arcn)
{
      struct stat sb;

      /*
       * we may be running as root, so we have to be sure that link target
       * is not a directory, so we lstat and check
       */
      if (lstat(arcn->ln_name, &sb) < 0) {
            syswarn(1,errno,"Unable to link to %s from %s", arcn->ln_name,
                arcn->name);
            return(-1);
      }

      if (S_ISDIR(sb.st_mode)) {
            paxwarn(1, "A hard link to the directory %s is not allowed",
                arcn->ln_name);
            return(-1);
      }

      return(mk_link(arcn->ln_name, &sb, arcn->name, 0));
}

/*
 * cross_lnk()
 *    Create a hard link to arcn->org_name from arcn->name. Only used in copy
 *    with the -l flag. No warning or error if this does not succeed (we will
 *    then just create the file)
 * Return:
 *    1 if copy() should try to create this file node
 *    0 if cross_lnk() ok, -1 for fatal flaw (like linking to self).
 */

int
cross_lnk(ARCHD *arcn)
{
      /*
       * try to make a link to original file (-l flag in copy mode). make
       * sure we do not try to link to directories in case we are running as
       * root (and it might succeed).
       */
      if (arcn->type == PAX_DIR)
            return(1);
      return(mk_link(arcn->org_name, &(arcn->sb), arcn->name, 1));
}

/*
 * chk_same()
 *    In copy mode if we are not trying to make hard links between the src
 *    and destinations, make sure we are not going to overwrite ourselves by
 *    accident. This slows things down a little, but we have to protect all
 *    those people who make typing errors.
 * Return:
 *    1 the target does not exist, go ahead and copy
 *    0 skip it file exists (-k) or may be the same as source file
 */

int
chk_same(ARCHD *arcn)
{
      struct stat sb;

      /*
       * if file does not exist, return. if file exists and -k, skip it
       * quietly
       */
      if (lstat(arcn->name, &sb) < 0)
            return(1);
      if (kflag)
            return(0);

      /*
       * better make sure the user does not have src == dest by mistake
       */
      if ((arcn->sb.st_dev == sb.st_dev) && (arcn->sb.st_ino == sb.st_ino)) {
            paxwarn(1, "Unable to copy %s, file would overwrite itself",
                arcn->name);
            return(0);
      }
      return(1);
}

/*
 * mk_link()
 *    try to make a hard link between two files. if ign set, we do not
 *    complain.
 * Return:
 *    0 if successful (or we are done with this file but no error, such as
 *    finding the from file exists and the user has set -k).
 *    1 when ign was set to indicates we could not make the link but we
 *    should try to copy/extract the file as that might work (and is an
 *    allowed option). -1 an error occurred.
 */

static int
mk_link(char *to, struct stat *to_sb, char *from, int ign)
{
      struct stat sb;
      int oerrno;

      /*
       * if from file exists, it has to be unlinked to make the link. If the
       * file exists and -k is set, skip it quietly
       */
      if (lstat(from, &sb) == 0) {
            if (kflag)
                  return(0);

            /*
             * make sure it is not the same file, protect the user
             */
            if ((to_sb->st_dev==sb.st_dev)&&(to_sb->st_ino == sb.st_ino)) {
                  paxwarn(1, "Unable to link file %s to itself", to);
                  return(-1);
            }

            /*
             * try to get rid of the file, based on the type
             */
            if (S_ISDIR(sb.st_mode)) {
                  if (rmdir(from) < 0) {
                        syswarn(1, errno, "Unable to remove %s", from);
                        return(-1);
                  }
            } else if (unlink(from) < 0) {
                  if (!ign) {
                        syswarn(1, errno, "Unable to remove %s", from);
                        return(-1);
                  }
                  return(1);
            }
      }

      /*
       * from file is gone (or did not exist), try to make the hard link.
       * if it fails, check the path and try it again (if chk_path() says to
       * try again)
       */
      for (;;) {
            if (link(to, from) == 0)
                  break;
            oerrno = errno;
            if (!nodirs && chk_path(from, to_sb->st_uid, to_sb->st_gid) == 0)
                  continue;
            if (!ign) {
                  syswarn(1, oerrno, "Could not link to %s from %s", to,
                      from);
                  return(-1);
            }
            return(1);
      }

      /*
       * all right the link was made
       */
      return(0);
}

/*
 * node_creat()
 *    create an entry in the file system (other than a file or hard link).
 *    If successful, sets uid/gid modes and times as required.
 * Return:
 *    0 if ok, -1 otherwise
 */

int
node_creat(ARCHD *arcn)
{
      int res;
      int ign = 0;
      int oerrno;
      int pass = 0;
      mode_t file_mode;
      struct stat sb;
      char target[MAXPATHLEN];
      char *nm = arcn->name;
      int len;

      /*
       * create node based on type, if that fails try to unlink the node and
       * try again. finally check the path and try again. As noted in the
       * file and link creation routines, this method seems to exhibit the
       * best performance in general use workloads.
       */
      file_mode = arcn->sb.st_mode & FILEBITS;

      for (;;) {
            switch (arcn->type) {
            case PAX_DIR:
                  /*
                   * If -h (or -L) was given in tar-mode, follow the
                   * potential symlink chain before trying to create the
                   * directory.
                   */
                  if (strcmp(NM_TAR, argv0) == 0 && Lflag) {
                        while (lstat(nm, &sb) == 0 &&
                            S_ISLNK(sb.st_mode)) {
                              len = readlink(nm, target,
                                  sizeof target - 1);
                              if (len == -1) {
                                    syswarn(0, errno,
                                       "cannot follow symlink %s in chain for %s",
                                        nm, arcn->name);
                                    res = -1;
                                    goto badlink;
                              }
                              target[len] = '\0';
                              nm = target;
                        }
                  }
                  res = mkdir(nm, file_mode);

badlink:
                  if (ign)
                        res = 0;
                  break;
            case PAX_CHR:
                  file_mode |= S_IFCHR;
                  res = mknod(nm, file_mode, arcn->sb.st_rdev);
                  break;
            case PAX_BLK:
                  file_mode |= S_IFBLK;
                  res = mknod(nm, file_mode, arcn->sb.st_rdev);
                  break;
            case PAX_FIF:
                  res = mkfifo(nm, file_mode);
                  break;
            case PAX_SCK:
                  /*
                   * Skip sockets, operation has no meaning under BSD
                   */
                  paxwarn(0,
                      "%s skipped. Sockets cannot be copied or extracted",
                      nm);
                  return(-1);
            case PAX_SLK:
                  res = symlink(arcn->ln_name, nm);
                  break;
            case PAX_CTG:
            case PAX_HLK:
            case PAX_HRG:
            case PAX_REG:
            default:
                  /*
                   * we should never get here
                   */
                  paxwarn(0, "%s has an unknown file type, skipping",
                        nm);
                  return(-1);
            }

            /*
             * if we were able to create the node break out of the loop,
             * otherwise try to unlink the node and try again. if that
             * fails check the full path and try a final time.
             */
            if (res == 0)
                  break;

            /*
             * we failed to make the node
             */
            oerrno = errno;
            if ((ign = unlnk_exist(nm, arcn->type)) < 0)
                  return(-1);

            if (++pass <= 1)
                  continue;

            if (nodirs || chk_path(nm,arcn->sb.st_uid,arcn->sb.st_gid) < 0) {
                  syswarn(1, oerrno, "Could not create: %s", nm);
                  return(-1);
            }
      }

      /*
       * we were able to create the node. set uid/gid, modes and times
       */
      if (pids)
            res = ((arcn->type == PAX_SLK) ?
                set_lids(nm, arcn->sb.st_uid, arcn->sb.st_gid) :
                set_ids(nm, arcn->sb.st_uid, arcn->sb.st_gid));
      else
            res = 0;

      /*
       * symlinks are done now.
       */
      if (arcn->type == PAX_SLK)
            return(0);

      /*
       * IMPORTANT SECURITY NOTE:
       * if not preserving mode or we cannot set uid/gid, then PROHIBIT any
       * set uid/gid bits
       */
      if (!pmode || res)
            arcn->sb.st_mode &= ~(SETBITS);
      if (pmode)
            set_pmode(nm, arcn->sb.st_mode);

      if (arcn->type == PAX_DIR && strcmp(NM_CPIO, argv0) != 0) {
            /*
             * Dirs must be processed again at end of extract to set times
             * and modes to agree with those stored in the archive. However
             * to allow extract to continue, we may have to also set owner
             * rights. This allows nodes in the archive that are children
             * of this directory to be extracted without failure. Both time
             * and modes will be fixed after the entire archive is read and
             * before pax exits.
             */
            if (access(nm, R_OK | W_OK | X_OK) < 0) {
                  if (lstat(nm, &sb) < 0) {
                        syswarn(0, errno,"Could not access %s (stat)",
                            arcn->name);
                        set_pmode(nm,file_mode | S_IRWXU);
                  } else {
                        /*
                         * We have to add rights to the dir, so we make
                         * sure to restore the mode. The mode must be
                         * restored AS CREATED and not as stored if
                         * pmode is not set.
                         */
                        set_pmode(nm,
                            ((sb.st_mode & FILEBITS) | S_IRWXU));
                        if (!pmode)
                              arcn->sb.st_mode = sb.st_mode;
                  }

                  /*
                   * we have to force the mode to what was set here,
                   * since we changed it from the default as created.
                   */
                  add_dir(nm, &(arcn->sb), 1);
            } else if (pmode || patime || pmtime)
                  add_dir(nm, &(arcn->sb), 0);
      }

      if (patime || pmtime)
            set_ftime(nm, arcn->sb.st_mtime, arcn->sb.st_atime, 0);
      return(0);
}

/*
 * unlnk_exist()
 *    Remove node from file system with the specified name. We pass the type
 *    of the node that is going to replace it. When we try to create a
 *    directory and find that it already exists, we allow processing to
 *    continue as proper modes etc will always be set for it later on.
 * Return:
 *    0 is ok to proceed, no file with the specified name exists
 *    -1 we were unable to remove the node, or we should not remove it (-k)
 *    1 we found a directory and we were going to create a directory.
 */

int
unlnk_exist(char *name, int type)
{
      struct stat sb;

      /*
       * the file does not exist, or -k we are done
       */
      if (lstat(name, &sb) < 0)
            return(0);
      if (kflag)
            return(-1);

      if (S_ISDIR(sb.st_mode)) {
            /*
             * try to remove a directory, if it fails and we were going to
             * create a directory anyway, tell the caller (return a 1)
             */
            if (rmdir(name) < 0) {
                  if (type == PAX_DIR)
                        return(1);
                  syswarn(1,errno,"Unable to remove directory %s", name);
                  return(-1);
            }
            return(0);
      }

      /*
       * try to get rid of all non-directory type nodes
       */
      if (unlink(name) < 0) {
            syswarn(1, errno, "Could not unlink %s", name);
            return(-1);
      }
      return(0);
}

/*
 * chk_path()
 *    We were trying to create some kind of node in the file system and it
 *    failed. chk_path() makes sure the path up to the node exists and is
 *    writeable. When we have to create a directory that is missing along the
 *    path somewhere, the directory we create will be set to the same
 *    uid/gid as the file has (when uid and gid are being preserved).
 *    NOTE: this routine is a real performance loss. It is only used as a
 *    last resort when trying to create entries in the file system.
 * Return:
 *    -1 when it could find nothing it is allowed to fix.
 *    0 otherwise
 */

int
chk_path(char *name, uid_t st_uid, gid_t st_gid)
{
      char *spt = name;
      struct stat sb;
      int retval = -1;

      /*
       * watch out for paths with nodes stored directly in / (e.g. /bozo)
       */
      if (*spt == '/')
            ++spt;

      for (;;) {
            /*
             * work forward from the first / and check each part of the path
             */
            spt = strchr(spt, '/');
            if (spt == NULL)
                  break;
            *spt = '\0';

            /*
             * if it exists we assume it is a directory, it is not within
             * the spec (at least it seems to read that way) to alter the
             * file system for nodes NOT EXPLICITLY stored on the archive.
             * If that assumption is changed, you would test the node here
             * and figure out how to get rid of it (probably like some
             * recursive unlink()) or fix up the directory permissions if
             * required (do an access()).
             */
            if (lstat(name, &sb) == 0) {
                  *(spt++) = '/';
                  continue;
            }

            /*
             * the path fails at this point, see if we can create the
             * needed directory and continue on
             */
            if (mkdir(name, S_IRWXU | S_IRWXG | S_IRWXO) < 0) {
                  *spt = '/';
                  retval = -1;
                  break;
            }

            /*
             * we were able to create the directory. We will tell the
             * caller that we found something to fix, and it is ok to try
             * and create the node again.
             */
            retval = 0;
            if (pids)
                  (void)set_ids(name, st_uid, st_gid);

            /*
             * make sure the user doesn't have some strange umask that
             * causes this newly created directory to be unusable. We fix
             * the modes and restore them back to the creation default at
             * the end of pax
             */
            if ((access(name, R_OK | W_OK | X_OK) < 0) &&
                (lstat(name, &sb) == 0)) {
                  set_pmode(name, ((sb.st_mode & FILEBITS) | S_IRWXU));
                  add_dir(name, &sb, 1);
            }
            *(spt++) = '/';
            continue;
      }
      return(retval);
}

/*
 * set_ftime()
 *    Set the access time and modification time for a named file. If frc
 *    is non-zero we force these times to be set even if the user did not
 *    request access and/or modification time preservation (this is also
 *    used by -t to reset access times).
 *    When ign is zero, only those times the user has asked for are set, the
 *    other ones are left alone. We do not assume the un-documented feature
 *    of many utimes() implementations that consider a 0 time value as a do
 *    not set request.
 */

void
set_ftime(char *fnm, time_t mtime, time_t atime, int frc)
{
      static struct timeval tv[2] = {{0L, 0L}, {0L, 0L}};
      struct stat sb;

      tv[0].tv_sec = (long)atime;
      tv[1].tv_sec = (long)mtime;
      if (!frc && (!patime || !pmtime)) {
            /*
             * if we are not forcing, only set those times the user wants
             * set. We get the current values of the times if we need them.
             */
            if (lstat(fnm, &sb) == 0) {
                  if (!patime)
                        tv[0].tv_sec = (long)sb.st_atime;
                  if (!pmtime)
                        tv[1].tv_sec = (long)sb.st_mtime;
            } else
                  syswarn(0,errno,"Unable to obtain file stats %s", fnm);
      }

      /*
       * set the times
       */
      if (utimes(fnm, tv) < 0)
            syswarn(1, errno, "Access/modification time set failed on: %s",
                fnm);
      return;
}

void
fset_ftime(char *fnm, int fd, time_t mtime, time_t atime, int frc)
{
      static struct timeval tv[2] = {{0L, 0L}, {0L, 0L}};
      struct stat sb;

      tv[0].tv_sec = (long)atime;
      tv[1].tv_sec = (long)mtime;
      if (!frc && (!patime || !pmtime)) {
            /*
             * if we are not forcing, only set those times the user wants
             * set. We get the current values of the times if we need them.
             */
            if (fstat(fd, &sb) == 0) {
                  if (!patime)
                        tv[0].tv_sec = (long)sb.st_atime;
                  if (!pmtime)
                        tv[1].tv_sec = (long)sb.st_mtime;
            } else
                  syswarn(0,errno,"Unable to obtain file stats %s", fnm);
      }
      /*
       * set the times
       */
      if (futimes(fd, tv) < 0)
            syswarn(1, errno, "Access/modification time set failed on: %s",
                fnm);
      return;
}

/*
 * set_ids()
 *    set the uid and gid of a file system node
 * Return:
 *    0 when set, -1 on failure
 */

int
set_ids(char *fnm, uid_t uid, gid_t gid)
{
      if (chown(fnm, uid, gid) < 0) {
            /*
             * ignore EPERM unless in verbose mode or being run by root.
             * if running as pax, POSIX requires a warning.
             */
            if (strcmp(NM_PAX, argv0) == 0 || errno != EPERM || vflag ||
                geteuid() == 0)
                  syswarn(1, errno, "Unable to set file uid/gid of %s",
                      fnm);
            return(-1);
      }
      return(0);
}

int
fset_ids(char *fnm, int fd, uid_t uid, gid_t gid)
{
      if (fchown(fd, uid, gid) < 0) {
            /*
             * ignore EPERM unless in verbose mode or being run by root.
             * if running as pax, POSIX requires a warning.
             */
            if (strcmp(NM_PAX, argv0) == 0 || errno != EPERM || vflag ||
                geteuid() == 0)
                  syswarn(1, errno, "Unable to set file uid/gid of %s",
                      fnm);
            return(-1);
      }
      return(0);
}

/*
 * set_lids()
 *    set the uid and gid of a file system node
 * Return:
 *    0 when set, -1 on failure
 */

int
set_lids(char *fnm, uid_t uid, gid_t gid)
{
      if (lchown(fnm, uid, gid) < 0) {
            /*
             * ignore EPERM unless in verbose mode or being run by root.
             * if running as pax, POSIX requires a warning.
             */
            if (strcmp(NM_PAX, argv0) == 0 || errno != EPERM || vflag ||
                geteuid() == 0)
                  syswarn(1, errno, "Unable to set file uid/gid of %s",
                      fnm);
            return(-1);
      }
      return(0);
}

/*
 * set_pmode()
 *    Set file access mode
 */

void
set_pmode(char *fnm, mode_t mode)
{
      mode &= ABITS;
      if (chmod(fnm, mode) < 0)
            syswarn(1, errno, "Could not set permissions on %s", fnm);
      return;
}

void
fset_pmode(char *fnm, int fd, mode_t mode)
{
      mode &= ABITS;
      if (fchmod(fd, mode) < 0)
            syswarn(1, errno, "Could not set permissions on %s", fnm);
      return;
}

/*
 * file_write()
 *    Write/copy a file (during copy or archive extract). This routine knows
 *    how to copy files with lseek holes in it. (Which are read as file
 *    blocks containing all 0's but do not have any file blocks associated
 *    with the data). Typical examples of these are files created by dbm
 *    variants (.pag files). While the file size of these files are huge, the
 *    actual storage is quite small (the files are sparse). The problem is
 *    the holes read as all zeros so are probably stored on the archive that
 *    way (there is no way to determine if the file block is really a hole,
 *    we only know that a file block of all zero's can be a hole).
 *    At this writing, no major archive format knows how to archive files
 *    with holes. However, on extraction (or during copy, -rw) we have to
 *    deal with these files. Without detecting the holes, the files can
 *    consume a lot of file space if just written to disk. This replacement
 *    for write when passed the basic allocation size of a file system block,
 *    uses lseek whenever it detects the input data is all 0 within that
 *    file block. In more detail, the strategy is as follows:
 *    While the input is all zero keep doing an lseek. Keep track of when we
 *    pass over file block boundaries. Only write when we hit a non zero
 *    input. once we have written a file block, we continue to write it to
 *    the end (we stop looking at the input). When we reach the start of the
 *    next file block, start checking for zero blocks again. Working on file
 *    block boundaries significantly reduces the overhead when copying files
 *    that are NOT very sparse. This overhead (when compared to a write) is
 *    almost below the measurement resolution on many systems. Without it,
 *    files with holes cannot be safely copied. It does has a side effect as
 *    it can put holes into files that did not have them before, but that is
 *    not a problem since the file contents are unchanged (in fact it saves
 *    file space). (Except on paging files for diskless clients. But since we
 *    cannot determine one of those file from here, we ignore them). If this
 *    ever ends up on a system where CTG files are supported and the holes
 *    are not desired, just do a conditional test in those routines that
 *    call file_write() and have it call write() instead. BEFORE CLOSING THE
 *    FILE, make sure to call file_flush() when the last write finishes with
 *    an empty block. A lot of file systems will not create an lseek hole at
 *    the end. In this case we drop a single 0 at the end to force the
 *    trailing 0's in the file.
 *    ---Parameters---
 *    rem: how many bytes left in this file system block
 *    isempt: have we written to the file block yet (is it empty)
 *    sz: basic file block allocation size
 *    cnt: number of bytes on this write
 *    str: buffer to write
 * Return:
 *    number of bytes written, -1 on write (or lseek) error.
 */

int
file_write(int fd, char *str, int cnt, int *rem, int *isempt, int sz,
      char *name)
{
      char *pt;
      char *end;
      int wcnt;
      char *st = str;
      char **strp;

      /*
       * while we have data to process
       */
      while (cnt) {
            if (!*rem) {
                  /*
                   * We are now at the start of file system block again
                   * (or what we think one is...). start looking for
                   * empty blocks again
                   */
                  *isempt = 1;
                  *rem = sz;
            }

            /*
             * only examine up to the end of the current file block or
             * remaining characters to write, whatever is smaller
             */
            wcnt = MIN(cnt, *rem);
            cnt -= wcnt;
            *rem -= wcnt;
            if (*isempt) {
                  /*
                   * have not written to this block yet, so we keep
                   * looking for zero's
                   */
                  pt = st;
                  end = st + wcnt;

                  /*
                   * look for a zero filled buffer
                   */
                  while ((pt < end) && (*pt == '\0'))
                        ++pt;

                  if (pt == end) {
                        /*
                         * skip, buf is empty so far
                         */
                        if (fd > -1 &&
                            lseek(fd, (off_t)wcnt, SEEK_CUR) < 0) {
                              syswarn(1,errno,"File seek on %s",
                                  name);
                              return(-1);
                        }
                        st = pt;
                        continue;
                  }
                  /*
                   * drat, the buf is not zero filled
                   */
                  *isempt = 0;
            }

            /*
             * have non-zero data in this file system block, have to write
             */
            switch (fd) {
            case -1:
                  strp = &gnu_name_string;
                  break;
            case -2:
                  strp = &gnu_link_string;
                  break;
            default:
                  strp = NULL;
                  break;
            }
            if (strp) {
                  if (*strp)
                        err(1, "WARNING! Major Internal Error! GNU hack Failing!");
                  *strp = malloc(wcnt + 1);
                  if (*strp == NULL) {
                        paxwarn(1, "Out of memory");
                        return(-1);
                  }
                  memcpy(*strp, st, wcnt);
                  (*strp)[wcnt] = '\0';
                  break;
            } else if (write(fd, st, wcnt) != wcnt) {
                  syswarn(1, errno, "Failed write to file %s", name);
                  return(-1);
            }
            st += wcnt;
      }
      return(st - str);
}

/*
 * file_flush()
 *    when the last file block in a file is zero, many file systems will not
 *    let us create a hole at the end. To get the last block with zeros, we
 *    write the last BYTE with a zero (back up one byte and write a zero).
 */

void
file_flush(int fd, char *fname, int isempt)
{
      static char blnk[] = "\0";

      /*
       * silly test, but make sure we are only called when the last block is
       * filled with all zeros.
       */
      if (!isempt)
            return;

      /*
       * move back one byte and write a zero
       */
      if (lseek(fd, (off_t)-1, SEEK_CUR) < 0) {
            syswarn(1, errno, "Failed seek on file %s", fname);
            return;
      }

      if (write(fd, blnk, 1) < 0)
            syswarn(1, errno, "Failed write to file %s", fname);
      return;
}

/*
 * rdfile_close()
 *    close a file we have beed reading (to copy or archive). If we have to
 *    reset access time (tflag) do so (the times are stored in arcn).
 */

void
rdfile_close(ARCHD *arcn, int *fd)
{
      /*
       * make sure the file is open
       */
      if (*fd < 0)
            return;

      (void)close(*fd);
      *fd = -1;
      if (!tflag)
            return;

      /*
       * user wants last access time reset
       */
      set_ftime(arcn->org_name, arcn->sb.st_mtime, arcn->sb.st_atime, 1);
      return;
}

/*
 * set_crc()
 *    read a file to calculate its crc. This is a real drag. Archive formats
 *    that have this, end up reading the file twice (we have to write the
 *    header WITH the crc before writing the file contents. Oh well...
 * Return:
 *    0 if was able to calculate the crc, -1 otherwise
 */

int
set_crc(ARCHD *arcn, int fd)
{
      int i;
      int res;
      off_t cpcnt = 0L;
      u_long size;
      u_int32_t crc = 0;
      char tbuf[FILEBLK];
      struct stat sb;

      if (fd < 0) {
            /*
             * hmm, no fd, should never happen. well no crc then.
             */
            arcn->crc = 0L;
            return(0);
      }

      if ((size = (u_long)arcn->sb.st_blksize) > (u_long)sizeof(tbuf))
            size = (u_long)sizeof(tbuf);

      /*
       * read all the bytes we think that there are in the file. If the user
       * is trying to archive an active file, forget this file.
       */
      for (;;) {
            if ((res = read(fd, tbuf, size)) <= 0)
                  break;
            cpcnt += res;
            for (i = 0; i < res; ++i)
                  crc += (tbuf[i] & 0xff);
      }

      /*
       * safety check. we want to avoid archiving files that are active as
       * they can create inconsistent archive copies.
       */
      if (cpcnt != arcn->sb.st_size)
            paxwarn(1, "File changed size %s", arcn->org_name);
      else if (fstat(fd, &sb) < 0)
            syswarn(1, errno, "Failed stat on %s", arcn->org_name);
      else if (arcn->sb.st_mtime != sb.st_mtime)
            paxwarn(1, "File %s was modified during read", arcn->org_name);
      else if (lseek(fd, (off_t)0L, SEEK_SET) < 0)
            syswarn(1, errno, "File rewind failed on: %s", arcn->org_name);
      else {
            arcn->crc = crc;
            return(0);
      }
      return(-1);
}

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