fd_name.c

#define _GNU_SOURCE

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <dirent.h>

#define FD_LINK_DIR "/proc/self/fd"
#define FD_LINK     FD_LINK_DIR "/%d"
#define DEV_NULL    "/dev/null"
#define DEV_ZERO    "/dev/zero"
#define BUFFER_SIZE 80

typedef int PIPE[2];

char *acc_types[3] = {"Write", "Read/Write", "Read"};
char *std_names[3] = {"STDIN", "STDOUT", "STDERR"};

void fd_print_info(int fd);
void fd_print_all();

int main()
{
    int fd_null, fd_zero, fd_tty;
    PIPE fd_pipe;
    
    fd_print_all();
    
    pipe(fd_pipe);
    
    fd_print_all();
    
    fd_null = open(DEV_NULL, O_RDONLY);
    fd_zero = open(DEV_ZERO, O_RDONLY);
    fd_tty = open("/dev/tty", O_RDONLY);
    
    fd_print_all();
    
    close(fd_tty);
    
    dup2(fd_zero, fd_null);
    dup2(STDOUT_FILENO, STDERR_FILENO);
    
    fd_print_all();
    
    close(fd_null);
    
    fd_print_all();
    
    return 0;
}

void fd_print_info(int fd)
{
    char f_name_buffer[80], link_buffer[80];
    int rd, acc_type, f_flags;
    
    f_flags = fcntl(fd, F_GETFL, 0);
    
    if (f_flags == -1) {
        if (errno == EBADF)
            printf("%d not open\n", fd);
        else
            printf("%d error\n", fd);
        return;
    }
    
    if((f_flags & O_ACCMODE) == O_WRONLY)
        acc_type = 0;
    if ((f_flags & O_ACCMODE) == O_RDWR)
        acc_type = 1;
    if ((f_flags & O_ACCMODE) == O_RDONLY)
        acc_type = 2;
    
    sprintf(f_name_buffer, FD_LINK, fd);
    
    rd = readlink(f_name_buffer, link_buffer, BUFFER_SIZE);
    link_buffer[rd] = '\0';
    
    printf("%d -> [%s], (%s) %s\n",
            fd, 
            link_buffer,
            acc_types[acc_type],
            (fd < 3 ? std_names[fd] : ""));
}

void fd_print_all()
{
    DIR *dirp;
    struct dirent *dp;
    int fd;
    
    if ((dirp = opendir(FD_LINK_DIR)) == NULL) {
        perror("Couldn't open FD dir");
        return;
    }
    
    do {
        if ((dp = readdir(dirp)) != NULL) {
            fd = -1;
            sscanf(dp->d_name, "%d", &fd);
            if (fd != -1)
                fd_print_info(fd);
        }
    } while (dp != NULL);
    
    putchar('\n');
    
    closedir(dirp);
}