close_range - close all file descriptors in a given range

#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <unistd.h>
#include <linux/close_range.h> /* Definition of CLOSE_RANGE_*
 constants */
int close_range(unsigned int first, unsigned int last, int flags);

The close_range() system call closes all open file descriptors from first to last (included).

Errors closing a given file descriptor are currently ignored.

flags is a bit mask containing 0 or more of the following:

CLOSE_RANGE_CLOEXEC (since Linux 5.11)

Set the close-on-exec flag on the specified file descriptors, rather than immediately closing them.

CLOSE_RANGE_UNSHARE

Unshare the specified file descriptors from any other processes before closing them, avoiding races with other threads sharing the file descriptor table.

On success, close_range() returns 0. On error, -1 is returned and errno is set to indicate the error.

The program shown below opens the files named in its command-line arguments, displays the list of files that it has opened (by iterating through the entries in /proc/PID/fd), uses close_range() to close all file descriptors greater than or equal to 3, and then once more displays the process's list of open files. The following example demonstrates the use of the program:

$ touch /tmp/a /tmp/b /tmp/c
$ ./a.out /tmp/a /tmp/b /tmp/c
/tmp/a opened as FD 3
/tmp/b opened as FD 4
/tmp/c opened as FD 5
/proc/self/fd/0 ==> /dev/pts/1
/proc/self/fd/1 ==> /dev/pts/1
/proc/self/fd/2 ==> /dev/pts/1
/proc/self/fd/3 ==> /tmp/a
/proc/self/fd/4 ==> /tmp/b
/proc/self/fd/5 ==> /tmp/b
/proc/self/fd/6 ==> /proc/9005/fd
========= About to call close_range() =======
/proc/self/fd/0 ==> /dev/pts/1
/proc/self/fd/1 ==> /dev/pts/1
/proc/self/fd/2 ==> /dev/pts/1
/proc/self/fd/3 ==> /proc/9005/fd

Note that the lines showing the pathname /proc/9005/fd result from the calls to opendir(3).

Program source

#define _GNU_SOURCE
#include <dirent.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
/* Show the contents of the symbolic links in /proc/self/fd */
static void
show_fds(void)
{
    DIR            *dirp;
    char           path[PATH_MAX], target[PATH_MAX];
    ssize_t        len;
    struct dirent  *dp;
    dirp = opendir("/proc/self/fd");
    if (dirp  == NULL) {
        perror("opendir");
        exit(EXIT_FAILURE);
    }
    for (;;) {
        dp = readdir(dirp);
        if (dp == NULL)
            break;
        if (dp->d_type == DT_LNK) {
            snprintf(path, sizeof(path), "/proc/self/fd/%s",
                     dp->d_name);
            len = readlink(path, target, sizeof(target));
            printf("%s ==> %.*s\n", path, (int) len, target);
        }
    }
    closedir(dirp);
}
int
main(int argc, char *argv[])
{
    int  fd;
    for (size_t j = 1; j < argc; j++) {
        fd = open(argv[j], O_RDONLY);
        if (fd == -1) {
            perror(argv[j]);
            exit(EXIT_FAILURE);
        }
        printf("%s opened as FD %d\n", argv[j], fd);
    }
    show_fds();
    printf("========= About to call close_range() =======\n");
    if (close_range(3, ~0U, 0) == -1) {
        perror("close_range");
        exit(EXIT_FAILURE);
    }
    show_fds();
    exit(EXIT_FAILURE);
}

close(2)