HAMMER VFS - Major retooling of the refcount mechanics, and fix a deadlock

[dragonfly.git] / bin / pax / file_subs.c

/*-
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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.
 *
 * @(#)file_subs.c      8.1 (Berkeley) 5/31/93
 * $FreeBSD: src/bin/pax/file_subs.c,v 1.12.2.1 2001/08/01 05:03:11 obrien Exp $
 * $DragonFly: src/bin/pax/file_subs.c,v 1.8 2006/09/27 21:58:08 pavalos Exp $
 */

#include <sys/types.h>
#include <sys/time.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <sys/uio.h>
#include <stdlib.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;
        if (close(fd) < 0)
                syswarn(0, errno, "Unable to close file descriptor on %s",
                    arcn->name);

        /*
         * 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 = set_ids(arcn->name, 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)
                set_pmode(arcn->name, arcn->sb.st_mode);
        if (patime || pmtime)
                set_ftime(arcn->name, arcn->sb.st_mtime, arcn->sb.st_atime, 0);
}

/*
 * 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;

        /*
         * 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:
                        res = mkdir(arcn->name, file_mode);
                        if (ign)
                                res = 0;
                        break;
                case PAX_CHR:
                        file_mode |= S_IFCHR;
                        res = mknod(arcn->name, file_mode, arcn->sb.st_rdev);
                        break;
                case PAX_BLK:
                        file_mode |= S_IFBLK;
                        res = mknod(arcn->name, file_mode, arcn->sb.st_rdev);
                        break;
                case PAX_FIF:
                        res = mkfifo(arcn->name, file_mode);
                        break;
                case PAX_SCK:
                        /*
                         * Skip sockets, operation has no meaning under BSD
                         */
                        paxwarn(0,
                            "%s skipped. Sockets cannot be copied or extracted",
                            arcn->name);
                        return(-1);
                case PAX_SLK:
                        res = symlink(arcn->ln_name, arcn->name);
                        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",
                                arcn->name);
                        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(arcn->name, arcn->type)) < 0)
                        return(-1);

                if (++pass <= 1)
                        continue;

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

        /*
         * we were able to create the node. set uid/gid, modes and times
         */
        if (pids)
                res = ((arcn->type == PAX_SLK) ?
                    set_lids(arcn->name, arcn->sb.st_uid, arcn->sb.st_gid) :
                    set_ids(arcn->name, 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(arcn->name, 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(arcn->name, R_OK | W_OK | X_OK) < 0) {
                        if (lstat(arcn->name, &sb) < 0) {
                                syswarn(0, errno,"Could not access %s (stat)",
                                    arcn->name);
                                set_pmode(arcn->name,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(arcn->name,
                                    ((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(arcn->name, arcn->nlen, &(arcn->sb), 1);
                } else if (pmode || patime || pmtime)
                        add_dir(arcn->name, arcn->nlen, &(arcn->sb), 0);
        }

        if (patime || pmtime)
                set_ftime(arcn->name, 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)
                        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, spt - 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;
}

/*
 * 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);
}

/*
 * 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;
}

/*
 * 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;

        /*
         * 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 (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
                 */
                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;

        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;
        unsigned long crc = 0L;
        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);
}