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/* These functions find the absolute path to the current working directory.  */

#include <stdlib.h>

#include <errno.h>

#include <sys/stat.h>

#include <dirent.h>

#include <string.h>

#include <sys/syscall.h>

#ifdef __NR_getcwd

#define __NR___syscall_getcwd __NR_getcwd

static inline

_syscall2(int, __syscall_getcwd, char *, buf, unsigned long, size);

#else

/* If the syscall is not present, we have to walk up the

 * directory tree till we hit the root.  Now we _could_

 * use /proc/self/cwd if /proc is mounted... That approach

 * is left an an exercise for the reader... */

/* Seems a few broken filesystems (like coda) don't like this */

/* #undef FAST_DIR_SEARCH_POSSIBLE on Linux */

/* Routine to find the step back down */

static char *search_dir(dev_t this_dev, ino_t this_ino, char *path_buf, int path_size)

{

        DIR *dp;

        struct dirent *d;

        char *ptr;

        int slen;

        struct stat st;

#ifdef FAST_DIR_SEARCH_POSSIBLE

        /* The test is for ELKS lib 0.0.9, this should be fixed in the real kernel */

        int slow_search = (sizeof(ino_t) != sizeof(d->d_ino));

#endif

        if (stat(path_buf, &st) < 0) {

                goto oops;

        }

#ifdef FAST_DIR_SEARCH_POSSIBLE

        if (this_dev != st.st_dev)

                slow_search = 1;

#endif

        slen = strlen(path_buf);

        ptr = path_buf + slen - 1;

        if (*ptr != '/') {

                if (slen + 2 > path_size) {

                        goto oops;

                }

                strcpy(++ptr, "/");

                slen++;

        }

        slen++;

        dp = opendir(path_buf);

        if (dp == 0) {

            goto oops;

        }

        while ((d = readdir(dp)) != 0) {

#ifdef FAST_DIR_SEARCH_POSSIBLE

                if (slow_search || this_ino == d->d_ino) {

#endif

                        if (slen + strlen(d->d_name) > path_size) {

                            goto oops;

                        }

                        strcpy(ptr + 1, d->d_name);

                        if (stat(path_buf, &st) < 0)

                                continue;

                        if (st.st_ino == this_ino && st.st_dev == this_dev) {

                                closedir(dp);

                                return path_buf;

                        }

#ifdef FAST_DIR_SEARCH_POSSIBLE

                }

#endif

        }

        closedir(dp);

        return 0;

oops:

        __set_errno(ERANGE);

        return 0;

}

/* Routine to go up tree */

static char *recurser(char *path_buf, int path_size, dev_t root_dev, ino_t root_ino)

{

        struct stat st;

        dev_t this_dev;

        ino_t this_ino;

        if (stat(path_buf, &st) < 0) {

            if (errno != EFAULT)

                goto oops;

            return 0;

        }

        this_dev = st.st_dev;

        this_ino = st.st_ino;

        if (this_dev == root_dev && this_ino == root_ino) {

                if (path_size < 2) {

                    goto oops;

                }

                strcpy(path_buf, "/");

                return path_buf;

        }

        if (strlen(path_buf) + 4 > path_size) {

            goto oops;

        }

        strcat(path_buf, "/..");

        if (recurser(path_buf, path_size, root_dev, root_ino) == 0)

                return 0;

        return search_dir(this_dev, this_ino, path_buf, path_size);

oops:

        __set_errno(ERANGE);

        return 0;

}

static inline

int __syscall_getcwd(char * buf, unsigned long size)

{

    int len;

    char *cwd;

    struct stat st;

    int olderrno;

    olderrno = errno;

    len = -1;

    cwd = recurser(buf, size, st.st_dev, st.st_ino);

    if (cwd) {

        len = strlen(buf);

        __set_errno(olderrno);

    }

    return len;

}

#endif

char *getcwd(char *buf, int size)

{

    int ret;

    char *path;

    size_t alloc_size = size;

    if (size == 0) {

        if (buf != NULL) {

            __set_errno(EINVAL);

            return NULL;

        }

        alloc_size = PATH_MAX;

    }

    path=buf;

    if (buf == NULL) {

        path = malloc(alloc_size);

        if (path == NULL)

            return NULL;

    }

    ret = __syscall_getcwd(path, alloc_size);

    if (ret >= 0)

    {

        if (buf == NULL && size == 0)

            buf = realloc(path, ret);

        if (buf == NULL)

            buf = path;

        return buf;

    }

    if (buf == NULL)

        free (path);

    return NULL;

}