/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1983, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 */

#include "namespace.h"
#include <sys/types.h>

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "un-namespace.h"

#include "gen-private.h"
#include "telldir.h"

DIR *
__opendir2(const char *name, int flags)
{
        int fd;
        DIR *dir;
        int saved_errno;

        if ((flags & (__DTF_READALL | __DTF_SKIPREAD)) != 0)
                return (NULL);
        if ((fd = _open(name, O_DIRECTORY | O_RDONLY | O_CLOEXEC)) == -1)
                return (NULL);

        dir = __opendir_common(fd, flags, false);
        if (dir == NULL) {
                saved_errno = errno;
                _close(fd);
                errno = saved_errno;
        }
        return (dir);
}

static int
opendir_compar(const void *p1, const void *p2)
{
        return (strcmp((*(const struct dirent * const *)p1)->d_name,
            (*(const struct dirent * const *)p2)->d_name));
}

/*
 * For a directory at the top of a unionfs stack, the entire directory's
 * contents are read and cached locally until the next call to rewinddir().
 * For the fdopendir() case, the initial seek position must be preserved.
 * For rewinddir(), the full directory should always be re-read from the
 * beginning.
 *
 * If an error occurs, the existing buffer and state of 'dirp' is left
 * unchanged.
 */
bool
_filldir(DIR *dirp, bool use_current_pos)
{
        struct dirent **dpv;
        char *buf, *ddptr, *ddeptr;
        off_t pos;
        int fd2, incr, len, n, saved_errno, space;

        len = 0;
        space = 0;
        buf = NULL;
        ddptr = NULL;

        /*
         * Use the system page size if that is a multiple of DIRBLKSIZ.
         * Hopefully this can be a big win someday by allowing page
         * trades to user space to be done by _getdirentries().
         */
        incr = getpagesize();
        if ((incr % DIRBLKSIZ) != 0)
                incr = DIRBLKSIZ;

        /*
         * The strategy here is to read all the directory
         * entries into a buffer, sort the buffer, and
         * remove duplicate entries by setting the inode
         * number to zero.
         *
         * We reopen the directory because _getdirentries()
         * on a MNT_UNION mount modifies the open directory,
         * making it refer to the lower directory after the
         * upper directory's entries are exhausted.
         * This would otherwise break software that uses
         * the directory descriptor for fchdir or *at
         * functions, such as fts.c.
         */
        if ((fd2 = _openat(dirp->dd_fd, ".", O_RDONLY | O_CLOEXEC)) == -1)
                return (false);

        if (use_current_pos) {
                pos = lseek(dirp->dd_fd, 0, SEEK_CUR);
                if (pos == -1 || lseek(fd2, pos, SEEK_SET) == -1) {
                        saved_errno = errno;
                        _close(fd2);
                        errno = saved_errno;
                        return (false);
                }
        }

        do {
                /*
                 * Always make at least DIRBLKSIZ bytes
                 * available to _getdirentries
                 */
                if (space < DIRBLKSIZ) {
                        space += incr;
                        len += incr;
                        buf = reallocf(buf, len);
                        if (buf == NULL) {
                                saved_errno = errno;
                                _close(fd2);
                                errno = saved_errno;
                                return (false);
                        }
                        ddptr = buf + (len - space);
                }

                n = _getdirentries(fd2, ddptr, space, &dirp->dd_seek);
                if (n > 0) {
                        ddptr += n;
                        space -= n;
                }
                if (n < 0) {
                        saved_errno = errno;
                        _close(fd2);
                        errno = saved_errno;
                        return (false);
                }
        } while (n > 0);
        _close(fd2);

        ddeptr = ddptr;

        /*
         * There is now a buffer full of (possibly) duplicate
         * names.
         */
        dirp->dd_buf = buf;

        /*
         * Go round this loop twice...
         *
         * Scan through the buffer, counting entries.
         * On the second pass, save pointers to each one.
         * Then sort the pointers and remove duplicate names.
         */
        for (dpv = NULL;;) {
                n = 0;
                ddptr = buf;
                while (ddptr < ddeptr) {
                        struct dirent *dp;

                        dp = (struct dirent *) ddptr;
                        if ((long)dp & 03L)
                                break;
                        if ((dp->d_reclen <= 0) ||
                            (dp->d_reclen > (ddeptr + 1 - ddptr)))
                                break;
                        ddptr += dp->d_reclen;
                        if (dp->d_fileno) {
                                if (dpv)
                                        dpv[n] = dp;
                                n++;
                        }
                }

                if (dpv) {
                        struct dirent *xp;

                        /*
                         * This sort must be stable.
                         */
                        mergesort(dpv, n, sizeof(*dpv), opendir_compar);

                        dpv[n] = NULL;
                        xp = NULL;

                        /*
                         * Scan through the buffer in sort order,
                         * zapping the inode number of any
                         * duplicate names.
                         */
                        for (n = 0; dpv[n]; n++) {
                                struct dirent *dp = dpv[n];

                                if ((xp == NULL) ||
                                    strcmp(dp->d_name, xp->d_name)) {
                                        xp = dp;
                                } else {
                                        dp->d_fileno = 0;
                                }
                                if (dp->d_type == DT_WHT &&
                                    (dirp->dd_flags & DTF_HIDEW))
                                        dp->d_fileno = 0;
                        }

                        free(dpv);
                        break;
                } else {
                        dpv = malloc((n+1) * sizeof(struct dirent *));
                        if (dpv == NULL)
                                break;
                }
        }

        dirp->dd_len = len;
        dirp->dd_size = ddptr - dirp->dd_buf;
        return (true);
}

/*
 * Return true if the file descriptor is associated with a file from a
 * union file system or from a file system mounted with the union flag.
 */
static bool
is_unionstack(int fd)
{
        /*
         * This call shouldn't fail, but if it does, just assume that the
         * answer is no.
         */
        return (_fcntl(fd, F_ISUNIONSTACK, 0) > 0);
}

/*
 * Common routine for opendir(3), __opendir2(3) and fdopendir(3).
 */
DIR *
__opendir_common(int fd, int flags, bool use_current_pos)
{
        DIR *dirp;
        ssize_t ret;
        int incr;
        int saved_errno;
        bool unionstack;

        if ((dirp = malloc(sizeof(DIR) + sizeof(struct _telldir))) == NULL)
                return (NULL);

        dirp->dd_buf = NULL;
        dirp->dd_fd = fd;
        dirp->dd_flags = flags;
        dirp->dd_loc = 0;
        dirp->dd_lock = NULL;
        dirp->dd_td = (struct _telldir *)((char *)dirp + sizeof(DIR));
        LIST_INIT(&dirp->dd_td->td_locq);
        dirp->dd_td->td_loccnt = 0;
        dirp->dd_compat_de = NULL;

        /*
         * Use the system page size if that is a multiple of DIRBLKSIZ.
         * Hopefully this can be a big win someday by allowing page
         * trades to user space to be done by _getdirentries().
         */
        incr = getpagesize();
        if ((incr % DIRBLKSIZ) != 0)
                incr = DIRBLKSIZ;

        /*
         * Determine whether this directory is the top of a union stack.
         */
        unionstack = false;
        if (flags & DTF_NODUP) {
                unionstack = is_unionstack(fd);
        }

        if (unionstack) {
                if (!_filldir(dirp, use_current_pos))
                        goto fail;
                dirp->dd_flags |= __DTF_READALL;
        } else {
                dirp->dd_len = incr;
                dirp->dd_buf = malloc(dirp->dd_len);
                if (dirp->dd_buf == NULL)
                        goto fail;
                if (use_current_pos) {
                        /*
                         * Read the first batch of directory entries
                         * to prime dd_seek.  This also checks if the
                         * fd passed to fdopendir() is a directory.
                         */
                        ret = _getdirentries(dirp->dd_fd,
                            dirp->dd_buf, dirp->dd_len, &dirp->dd_seek);
                        if (ret < 0)
                                goto fail;
                        dirp->dd_size = (size_t)ret;
                        dirp->dd_flags |= __DTF_SKIPREAD;
                } else {
                        dirp->dd_size = 0;
                        dirp->dd_seek = 0;
                }
        }

        return (dirp);

fail:
        saved_errno = errno;
        free(dirp->dd_buf);
        free(dirp);
        errno = saved_errno;
        return (NULL);
}