Test: add disable syscalls when none are enabled

[lttng-tools.git] / src / common / utils.c

/*
 * Copyright (C) 2012 - David Goulet <dgoulet@efficios.com>
 * Copyright (C) 2013 - Raphaël Beamonte <raphael.beamonte@gmail.com>
 * Copyright (C) 2013 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License, version 2 only, as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#define _GNU_SOURCE
#include <assert.h>
#include <ctype.h>
#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <inttypes.h>
#include <grp.h>
#include <pwd.h>
#include <sys/file.h>

#include <common/common.h>
#include <common/runas.h>

#include "utils.h"
#include "defaults.h"

/*
 * Return a partial realpath(3) of the path even if the full path does not
 * exist. For instance, with /tmp/test1/test2/test3, if test2/ does not exist
 * but the /tmp/test1 does, the real path for /tmp/test1 is concatened with
 * /test2/test3 then returned. In normal time, realpath(3) fails if the end
 * point directory does not exist.
 * In case resolved_path is NULL, the string returned was allocated in the
 * function and thus need to be freed by the caller. The size argument allows
 * to specify the size of the resolved_path argument if given, or the size to
 * allocate.
 */
LTTNG_HIDDEN
char *utils_partial_realpath(const char *path, char *resolved_path, size_t size)
{
        char *cut_path, *try_path = NULL, *try_path_prev = NULL;
        const char *next, *prev, *end;

        /* Safety net */
        if (path == NULL) {
                goto error;
        }

        /*
         * Identify the end of the path, we don't want to treat the
         * last char if it is a '/', we will just keep it on the side
         * to be added at the end, and return a value coherent with
         * the path given as argument
         */
        end = path + strlen(path);
        if (*(end-1) == '/') {
                end--;
        }

        /* Initiate the values of the pointers before looping */
        next = path;
        prev = next;
        /* Only to ensure try_path is not NULL to enter the while */
        try_path = (char *)next;

        /* Resolve the canonical path of the first part of the path */
        while (try_path != NULL && next != end) {
                /*
                 * If there is not any '/' left, we want to try with
                 * the full path
                 */
                next = strpbrk(next + 1, "/");
                if (next == NULL) {
                        next = end;
                }

                /* Cut the part we will be trying to resolve */
                cut_path = strndup(path, next - path);

                /* Try to resolve this part */
                try_path = realpath((char *)cut_path, NULL);
                if (try_path == NULL) {
                        /*
                         * There was an error, we just want to be assured it
                         * is linked to an unexistent directory, if it's another
                         * reason, we spawn an error
                         */
                        switch (errno) {
                        case ENOENT:
                                /* Ignore the error */
                                break;
                        default:
                                PERROR("realpath (partial_realpath)");
                                goto error;
                                break;
                        }
                } else {
                        /* Save the place we are before trying the next step */
                        free(try_path_prev);
                        try_path_prev = try_path;
                        prev = next;
                }

                /* Free the allocated memory */
                free(cut_path);
        };

        /* Allocate memory for the resolved path if necessary */
        if (resolved_path == NULL) {
                resolved_path = zmalloc(size);
                if (resolved_path == NULL) {
                        PERROR("zmalloc resolved path");
                        goto error;
                }
        }

        /*
         * If we were able to solve at least partially the path, we can concatenate
         * what worked and what didn't work
         */
        if (try_path_prev != NULL) {
                /* If we risk to concatenate two '/', we remove one of them */
                if (try_path_prev[strlen(try_path_prev) - 1] == '/' && prev[0] == '/') {
                        try_path_prev[strlen(try_path_prev) - 1] = '\0';
                }

                /*
                 * Duplicate the memory used by prev in case resolved_path and
                 * path are pointers for the same memory space
                 */
                cut_path = strdup(prev);

                /* Concatenate the strings */
                snprintf(resolved_path, size, "%s%s", try_path_prev, cut_path);

                /* Free the allocated memory */
                free(cut_path);
                free(try_path_prev);
        /*
         * Else, we just copy the path in our resolved_path to
         * return it as is
         */
        } else {
                strncpy(resolved_path, path, size);
        }

        /* Then we return the 'partially' resolved path */
        return resolved_path;

error:
        free(resolved_path);
        return NULL;
}

/*
 * Make a full resolution of the given path even if it doesn't exist.
 * This function uses the utils_partial_realpath function to resolve
 * symlinks and relatives paths at the start of the string, and
 * implements functionnalities to resolve the './' and '../' strings
 * in the middle of a path. This function is only necessary because
 * realpath(3) does not accept to resolve unexistent paths.
 * The returned string was allocated in the function, it is thus of
 * the responsibility of the caller to free this memory.
 */
LTTNG_HIDDEN
char *utils_expand_path(const char *path)
{
        char *next, *previous, *slash, *start_path, *absolute_path = NULL;
        char *last_token;
        int is_dot, is_dotdot;

        /* Safety net */
        if (path == NULL) {
                goto error;
        }

        /* Allocate memory for the absolute_path */
        absolute_path = zmalloc(PATH_MAX);
        if (absolute_path == NULL) {
                PERROR("zmalloc expand path");
                goto error;
        }

        /*
         * If the path is not already absolute nor explicitly relative,
         * consider we're in the current directory
         */
        if (*path != '/' && strncmp(path, "./", 2) != 0 &&
                        strncmp(path, "../", 3) != 0) {
                snprintf(absolute_path, PATH_MAX, "./%s", path);
        /* Else, we just copy the path */
        } else {
                strncpy(absolute_path, path, PATH_MAX);
        }

        /* Resolve partially our path */
        absolute_path = utils_partial_realpath(absolute_path,
                        absolute_path, PATH_MAX);

        /* As long as we find '/./' in the working_path string */
        while ((next = strstr(absolute_path, "/./"))) {

                /* We prepare the start_path not containing it */
                start_path = strndup(absolute_path, next - absolute_path);

                /* And we concatenate it with the part after this string */
                snprintf(absolute_path, PATH_MAX, "%s%s", start_path, next + 2);

                free(start_path);
        }

        /* As long as we find '/../' in the working_path string */
        while ((next = strstr(absolute_path, "/../"))) {
                /* We find the last level of directory */
                previous = absolute_path;
                while ((slash = strpbrk(previous, "/")) && slash != next) {
                        previous = slash + 1;
                }

                /* Then we prepare the start_path not containing it */
                start_path = strndup(absolute_path, previous - absolute_path);

                /* And we concatenate it with the part after the '/../' */
                snprintf(absolute_path, PATH_MAX, "%s%s", start_path, next + 4);

                /* We can free the memory used for the start path*/
                free(start_path);

                /* Then we verify for symlinks using partial_realpath */
                absolute_path = utils_partial_realpath(absolute_path,
                                absolute_path, PATH_MAX);
        }

        /* Identify the last token */
        last_token = strrchr(absolute_path, '/');

        /* Verify that this token is not a relative path */
        is_dotdot = (strcmp(last_token, "/..") == 0);
        is_dot = (strcmp(last_token, "/.") == 0);

        /* If it is, take action */
        if (is_dot || is_dotdot) {
                /* For both, remove this token */
                *last_token = '\0';

                /* If it was a reference to parent directory, go back one more time */
                if (is_dotdot) {
                        last_token = strrchr(absolute_path, '/');

                        /* If there was only one level left, we keep the first '/' */
                        if (last_token == absolute_path) {
                                last_token++;
                        }

                        *last_token = '\0';
                }
        }

        return absolute_path;

error:
        free(absolute_path);
        return NULL;
}

/*
 * Create a pipe in dst.
 */
LTTNG_HIDDEN
int utils_create_pipe(int *dst)
{
        int ret;

        if (dst == NULL) {
                return -1;
        }

        ret = pipe(dst);
        if (ret < 0) {
                PERROR("create pipe");
        }

        return ret;
}

/*
 * Create pipe and set CLOEXEC flag to both fd.
 *
 * Make sure the pipe opened by this function are closed at some point. Use
 * utils_close_pipe().
 */
LTTNG_HIDDEN
int utils_create_pipe_cloexec(int *dst)
{
        int ret, i;

        if (dst == NULL) {
                return -1;
        }

        ret = utils_create_pipe(dst);
        if (ret < 0) {
                goto error;
        }

        for (i = 0; i < 2; i++) {
                ret = fcntl(dst[i], F_SETFD, FD_CLOEXEC);
                if (ret < 0) {
                        PERROR("fcntl pipe cloexec");
                        goto error;
                }
        }

error:
        return ret;
}

/*
 * Create pipe and set fd flags to FD_CLOEXEC and O_NONBLOCK.
 *
 * Make sure the pipe opened by this function are closed at some point. Use
 * utils_close_pipe(). Using pipe() and fcntl rather than pipe2() to
 * support OSes other than Linux 2.6.23+.
 */
LTTNG_HIDDEN
int utils_create_pipe_cloexec_nonblock(int *dst)
{
        int ret, i;

        if (dst == NULL) {
                return -1;
        }

        ret = utils_create_pipe(dst);
        if (ret < 0) {
                goto error;
        }

        for (i = 0; i < 2; i++) {
                ret = fcntl(dst[i], F_SETFD, FD_CLOEXEC);
                if (ret < 0) {
                        PERROR("fcntl pipe cloexec");
                        goto error;
                }
                /*
                 * Note: we override any flag that could have been
                 * previously set on the fd.
                 */
                ret = fcntl(dst[i], F_SETFL, O_NONBLOCK);
                if (ret < 0) {
                        PERROR("fcntl pipe nonblock");
                        goto error;
                }
        }

error:
        return ret;
}

/*
 * Close both read and write side of the pipe.
 */
LTTNG_HIDDEN
void utils_close_pipe(int *src)
{
        int i, ret;

        if (src == NULL) {
                return;
        }

        for (i = 0; i < 2; i++) {
                /* Safety check */
                if (src[i] < 0) {
                        continue;
                }

                ret = close(src[i]);
                if (ret) {
                        PERROR("close pipe");
                }
        }
}

/*
 * Create a new string using two strings range.
 */
LTTNG_HIDDEN
char *utils_strdupdelim(const char *begin, const char *end)
{
        char *str;

        str = zmalloc(end - begin + 1);
        if (str == NULL) {
                PERROR("zmalloc strdupdelim");
                goto error;
        }

        memcpy(str, begin, end - begin);
        str[end - begin] = '\0';

error:
        return str;
}

/*
 * Set CLOEXEC flag to the give file descriptor.
 */
LTTNG_HIDDEN
int utils_set_fd_cloexec(int fd)
{
        int ret;

        if (fd < 0) {
                ret = -EINVAL;
                goto end;
        }

        ret = fcntl(fd, F_SETFD, FD_CLOEXEC);
        if (ret < 0) {
                PERROR("fcntl cloexec");
                ret = -errno;
        }

end:
        return ret;
}

/*
 * Create pid file to the given path and filename.
 */
LTTNG_HIDDEN
int utils_create_pid_file(pid_t pid, const char *filepath)
{
        int ret;
        FILE *fp;

        assert(filepath);

        fp = fopen(filepath, "w");
        if (fp == NULL) {
                PERROR("open pid file %s", filepath);
                ret = -1;
                goto error;
        }

        ret = fprintf(fp, "%d\n", pid);
        if (ret < 0) {
                PERROR("fprintf pid file");
        }

        fclose(fp);
        DBG("Pid %d written in file %s", pid, filepath);
error:
        return ret;
}

/*
 * Create lock file to the given path and filename.
 * Returns the associated file descriptor, -1 on error.
 */
LTTNG_HIDDEN
int utils_create_lock_file(const char *filepath)
{
        int ret;
        int fd;

        assert(filepath);

        fd = open(filepath, O_CREAT,
                O_WRONLY | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP);
        if (fd < 0) {
                PERROR("open lock file %s", filepath);
                ret = -1;
                goto error;
        }

        /*
         * Attempt to lock the file. If this fails, there is
         * already a process using the same lock file running
         * and we should exit.
         */
        ret = flock(fd, LOCK_EX | LOCK_NB);
        if (ret) {
                WARN("Could not get lock file %s, another instance is running.",
                        filepath);
                close(fd);
                fd = ret;
                goto error;
        }

error:
        return fd;
}

/*
 * Recursively create directory using the given path and mode.
 *
 * On success, return 0 else a negative error code.
 */
LTTNG_HIDDEN
int utils_mkdir_recursive(const char *path, mode_t mode)
{
        char *p, tmp[PATH_MAX];
        size_t len;
        int ret;

        assert(path);

        ret = snprintf(tmp, sizeof(tmp), "%s", path);
        if (ret < 0) {
                PERROR("snprintf mkdir");
                goto error;
        }

        len = ret;
        if (tmp[len - 1] == '/') {
                tmp[len - 1] = 0;
        }

        for (p = tmp + 1; *p; p++) {
                if (*p == '/') {
                        *p = 0;
                        if (tmp[strlen(tmp) - 1] == '.' &&
                                        tmp[strlen(tmp) - 2] == '.' &&
                                        tmp[strlen(tmp) - 3] == '/') {
                                ERR("Using '/../' is not permitted in the trace path (%s)",
                                                tmp);
                                ret = -1;
                                goto error;
                        }
                        ret = mkdir(tmp, mode);
                        if (ret < 0) {
                                if (errno != EEXIST) {
                                        PERROR("mkdir recursive");
                                        ret = -errno;
                                        goto error;
                                }
                        }
                        *p = '/';
                }
        }

        ret = mkdir(tmp, mode);
        if (ret < 0) {
                if (errno != EEXIST) {
                        PERROR("mkdir recursive last piece");
                        ret = -errno;
                } else {
                        ret = 0;
                }
        }

error:
        return ret;
}

/*
 * Create the stream tracefile on disk.
 *
 * Return 0 on success or else a negative value.
 */
LTTNG_HIDDEN
int utils_create_stream_file(const char *path_name, char *file_name, uint64_t size,
                uint64_t count, int uid, int gid, char *suffix)
{
        int ret, out_fd, flags, mode;
        char full_path[PATH_MAX], *path_name_suffix = NULL, *path;
        char *extra = NULL;

        assert(path_name);
        assert(file_name);

        ret = snprintf(full_path, sizeof(full_path), "%s/%s",
                        path_name, file_name);
        if (ret < 0) {
                PERROR("snprintf create output file");
                goto error;
        }

        /* Setup extra string if suffix or/and a count is needed. */
        if (size > 0 && suffix) {
                ret = asprintf(&extra, "_%" PRIu64 "%s", count, suffix);
        } else if (size > 0) {
                ret = asprintf(&extra, "_%" PRIu64, count);
        } else if (suffix) {
                ret = asprintf(&extra, "%s", suffix);
        }
        if (ret < 0) {
                PERROR("Allocating extra string to name");
                goto error;
        }

        /*
         * If we split the trace in multiple files, we have to add the count at the
         * end of the tracefile name
         */
        if (extra) {
                ret = asprintf(&path_name_suffix, "%s%s", full_path, extra);
                if (ret < 0) {
                        PERROR("Allocating path name with extra string");
                        goto error_free_suffix;
                }
                path = path_name_suffix;
        } else {
                path = full_path;
        }

        flags = O_WRONLY | O_CREAT | O_TRUNC;
        /* Open with 660 mode */
        mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;

        if (uid < 0 || gid < 0) {
                out_fd = open(path, flags, mode);
        } else {
                out_fd = run_as_open(path, flags, mode, uid, gid);
        }
        if (out_fd < 0) {
                PERROR("open stream path %s", path);
                goto error_open;
        }
        ret = out_fd;

error_open:
        free(path_name_suffix);
error_free_suffix:
        free(extra);
error:
        return ret;
}

/*
 * Change the output tracefile according to the given size and count The
 * new_count pointer is set during this operation.
 *
 * From the consumer, the stream lock MUST be held before calling this function
 * because we are modifying the stream status.
 *
 * Return 0 on success or else a negative value.
 */
LTTNG_HIDDEN
int utils_rotate_stream_file(char *path_name, char *file_name, uint64_t size,
                uint64_t count, int uid, int gid, int out_fd, uint64_t *new_count,
                int *stream_fd)
{
        int ret;

        assert(new_count);
        assert(stream_fd);

        ret = close(out_fd);
        if (ret < 0) {
                PERROR("Closing tracefile");
                goto error;
        }

        if (count > 0) {
                *new_count = (*new_count + 1) % count;
        } else {
                (*new_count)++;
        }

        ret = utils_create_stream_file(path_name, file_name, size, *new_count,
                        uid, gid, 0);
        if (ret < 0) {
                goto error;
        }
        *stream_fd = ret;

        /* Success. */
        ret = 0;

error:
        return ret;
}


/**
 * Parse a string that represents a size in human readable format. It
 * supports decimal integers suffixed by 'k', 'K', 'M' or 'G'.
 *
 * The suffix multiply the integer by:
 * 'k': 1024
 * 'M': 1024^2
 * 'G': 1024^3
 *
 * @param str   The string to parse.
 * @param size  Pointer to a uint64_t that will be filled with the
 *              resulting size.
 *
 * @return 0 on success, -1 on failure.
 */
LTTNG_HIDDEN
int utils_parse_size_suffix(const char * const str, uint64_t * const size)
{
        int ret;
        uint64_t base_size;
        long shift = 0;
        const char *str_end;
        char *num_end;

        if (!str) {
                DBG("utils_parse_size_suffix: received a NULL string.");
                ret = -1;
                goto end;
        }

        /* strtoull will accept a negative number, but we don't want to. */
        if (strchr(str, '-') != NULL) {
                DBG("utils_parse_size_suffix: invalid size string, should not contain '-'.");
                ret = -1;
                goto end;
        }

        /* str_end will point to the \0 */
        str_end = str + strlen(str);
        errno = 0;
        base_size = strtoull(str, &num_end, 0);
        if (errno != 0) {
                PERROR("utils_parse_size_suffix strtoull");
                ret = -1;
                goto end;
        }

        if (num_end == str) {
                /* strtoull parsed nothing, not good. */
                DBG("utils_parse_size_suffix: strtoull had nothing good to parse.");
                ret = -1;
                goto end;
        }

        /* Check if a prefix is present. */
        switch (*num_end) {
        case 'G':
                shift = GIBI_LOG2;
                num_end++;
                break;
        case 'M': /*  */
                shift = MEBI_LOG2;
                num_end++;
                break;
        case 'K':
        case 'k':
                shift = KIBI_LOG2;
                num_end++;
                break;
        case '\0':
                break;
        default:
                DBG("utils_parse_size_suffix: invalid suffix.");
                ret = -1;
                goto end;
        }

        /* Check for garbage after the valid input. */
        if (num_end != str_end) {
                DBG("utils_parse_size_suffix: Garbage after size string.");
                ret = -1;
                goto end;
        }

        *size = base_size << shift;

        /* Check for overflow */
        if ((*size >> shift) != base_size) {
                DBG("utils_parse_size_suffix: oops, overflow detected.");
                ret = -1;
                goto end;
        }

        ret = 0;
end:
        return ret;
}

/*
 * fls: returns the position of the most significant bit.
 * Returns 0 if no bit is set, else returns the position of the most
 * significant bit (from 1 to 32 on 32-bit, from 1 to 64 on 64-bit).
 */
#if defined(__i386) || defined(__x86_64)
static inline unsigned int fls_u32(uint32_t x)
{
        int r;

        asm("bsrl %1,%0\n\t"
                "jnz 1f\n\t"
                "movl $-1,%0\n\t"
                "1:\n\t"
                : "=r" (r) : "rm" (x));
        return r + 1;
}
#define HAS_FLS_U32
#endif

#ifndef HAS_FLS_U32
static __attribute__((unused)) unsigned int fls_u32(uint32_t x)
{
        unsigned int r = 32;

        if (!x) {
                return 0;
        }
        if (!(x & 0xFFFF0000U)) {
                x <<= 16;
                r -= 16;
        }
        if (!(x & 0xFF000000U)) {
                x <<= 8;
                r -= 8;
        }
        if (!(x & 0xF0000000U)) {
                x <<= 4;
                r -= 4;
        }
        if (!(x & 0xC0000000U)) {
                x <<= 2;
                r -= 2;
        }
        if (!(x & 0x80000000U)) {
                x <<= 1;
                r -= 1;
        }
        return r;
}
#endif

/*
 * Return the minimum order for which x <= (1UL << order).
 * Return -1 if x is 0.
 */
LTTNG_HIDDEN
int utils_get_count_order_u32(uint32_t x)
{
        if (!x) {
                return -1;
        }

        return fls_u32(x - 1);
}

/**
 * Obtain the value of LTTNG_HOME environment variable, if exists.
 * Otherwise returns the value of HOME.
 */
LTTNG_HIDDEN
char *utils_get_home_dir(void)
{
        char *val = NULL;
        struct passwd *pwd;

        val = getenv(DEFAULT_LTTNG_HOME_ENV_VAR);
        if (val != NULL) {
                goto end;
        }
        val = getenv(DEFAULT_LTTNG_FALLBACK_HOME_ENV_VAR);
        if (val != NULL) {
                goto end;
        }

        /* Fallback on the password file entry. */
        pwd = getpwuid(getuid());
        if (!pwd) {
                goto end;
        }
        val = pwd->pw_dir;

        DBG3("Home directory is '%s'", val);

end:
        return val;
}

/**
 * Get user's home directory. Dynamically allocated, must be freed
 * by the caller.
 */
LTTNG_HIDDEN
char *utils_get_user_home_dir(uid_t uid)
{
        struct passwd pwd;
        struct passwd *result;
        char *home_dir = NULL;
        char *buf = NULL;
        long buflen;
        int ret;

        buflen = sysconf(_SC_GETPW_R_SIZE_MAX);
        if (buflen == -1) {
                goto end;
        }
retry:
        buf = zmalloc(buflen);
        if (!buf) {
                goto end;
        }

        ret = getpwuid_r(uid, &pwd, buf, buflen, &result);
        if (ret || !result) {
                if (ret == ERANGE) {
                        free(buf);
                        buflen *= 2;
                        goto retry;
                }
                goto end;
        }

        home_dir = strdup(pwd.pw_dir);
end:
        free(buf);
        return home_dir;
}

/*
 * Obtain the value of LTTNG_KMOD_PROBES environment variable, if exists.
 * Otherwise returns NULL.
 */
LTTNG_HIDDEN
char *utils_get_kmod_probes_list(void)
{
        return getenv(DEFAULT_LTTNG_KMOD_PROBES);
}

/*
 * Obtain the value of LTTNG_EXTRA_KMOD_PROBES environment variable, if
 * exists. Otherwise returns NULL.
 */
LTTNG_HIDDEN
char *utils_get_extra_kmod_probes_list(void)
{
        return getenv(DEFAULT_LTTNG_EXTRA_KMOD_PROBES);
}

/*
 * With the given format, fill dst with the time of len maximum siz.
 *
 * Return amount of bytes set in the buffer or else 0 on error.
 */
LTTNG_HIDDEN
size_t utils_get_current_time_str(const char *format, char *dst, size_t len)
{
        size_t ret;
        time_t rawtime;
        struct tm *timeinfo;

        assert(format);
        assert(dst);

        /* Get date and time for session path */
        time(&rawtime);
        timeinfo = localtime(&rawtime);
        ret = strftime(dst, len, format, timeinfo);
        if (ret == 0) {
                ERR("Unable to strftime with format %s at dst %p of len %zu", format,
                                dst, len);
        }

        return ret;
}

/*
 * Return the group ID matching name, else 0 if it cannot be found.
 */
LTTNG_HIDDEN
gid_t utils_get_group_id(const char *name)
{
        struct group *grp;

        grp = getgrnam(name);
        if (!grp) {
                static volatile int warn_once;

                if (!warn_once) {
                        WARN("No tracing group detected");
                        warn_once = 1;
                }
                return 0;
        }
        return grp->gr_gid;
}

/*
 * Return a newly allocated option string. This string is to be used as the
 * optstring argument of getopt_long(), see GETOPT(3). opt_count is the number
 * of elements in the long_options array. Returns NULL if the string's
 * allocation fails.
 */
LTTNG_HIDDEN
char *utils_generate_optstring(const struct option *long_options,
                size_t opt_count)
{
        int i;
        size_t string_len = opt_count, str_pos = 0;
        char *optstring;

        /*
         * Compute the necessary string length. One letter per option, two when an
         * argument is necessary, and a trailing NULL.
         */
        for (i = 0; i < opt_count; i++) {
                string_len += long_options[i].has_arg ? 1 : 0;
        }

        optstring = zmalloc(string_len);
        if (!optstring) {
                goto end;
        }

        for (i = 0; i < opt_count; i++) {
                if (!long_options[i].name) {
                        /* Got to the trailing NULL element */
                        break;
                }

                optstring[str_pos++] = (char)long_options[i].val;
                if (long_options[i].has_arg) {
                        optstring[str_pos++] = ':';
                }
        }

end:
        return optstring;
}