NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

GETDENTS(2)               Linux Programmer's Manual              GETDENTS(2)

NAME         top

       getdents - get directory entries

SYNOPSIS         top

       int getdents(unsigned int fd, struct linux_dirent *dirp,
                    unsigned int count);

       Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION         top

       This is not the function you are interested in.  Look at readdir(3)
       for the POSIX conforming C library interface.  This page documents
       the bare kernel system call interface.

       The system call getdents() reads several linux_dirent structures from
       the directory referred to by the open file descriptor fd into the
       buffer pointed to by dirp.  The argument count specifies the size of
       that buffer.

       The linux_dirent structure is declared as follows:

           struct linux_dirent {
               unsigned long  d_ino;     /* Inode number */
               unsigned long  d_off;     /* Offset to next linux_dirent */
               unsigned short d_reclen;  /* Length of this linux_dirent */
               char           d_name[];  /* Filename (null-terminated) */
                                 /* length is actually (d_reclen - 2 -
                                    offsetof(struct linux_dirent, d_name)) */
               /*
               char           pad;       // Zero padding byte
               char           d_type;    // File type (only since Linux
                                         // 2.6.4); offset is (d_reclen - 1)
               */

           }

       d_ino is an inode number.  d_off is the distance from the start of
       the directory to the start of the next linux_dirent.  d_reclen is the
       size of this entire linux_dirent.  d_name is a null-terminated
       filename.

       d_type is a byte at the end of the structure that indicates the file
       type.  It contains one of the following values (defined in
       <dirent.h>):

       DT_BLK      This is a block device.

       DT_CHR      This is a character device.

       DT_DIR      This is a directory.

       DT_FIFO     This is a named pipe (FIFO).

       DT_LNK      This is a symbolic link.

       DT_REG      This is a regular file.

       DT_SOCK     This is a UNIX domain socket.

       DT_UNKNOWN  The file type is unknown.

       The d_type field is implemented since Linux 2.6.4.  It occupies a
       space that was previously a zero-filled padding byte in the
       linux_dirent structure.  Thus, on kernels before 2.6.3, attempting to
       access this field always provides the value 0 (DT_UNKNOWN).

       Currently, only some filesystems (among them: Btrfs, ext2, ext3, and
       ext4) have full support for returning the file type in d_type.  All
       applications must properly handle a return of DT_UNKNOWN.

RETURN VALUE         top

       On success, the number of bytes read is returned.  On end of
       directory, 0 is returned.  On error, -1 is returned, and errno is set
       appropriately.

ERRORS         top

       EBADF  Invalid file descriptor fd.

       EFAULT Argument points outside the calling process's address space.

       EINVAL Result buffer is too small.

       ENOENT No such directory.

       ENOTDIR
              File descriptor does not refer to a directory.

CONFORMING TO         top

       SVr4.

NOTES         top

       Glibc does not provide a wrapper for this system call; call it using
       syscall(2).  You will need to define the linux_dirent structure
       yourself.  However, you probably want to use readdir(3) instead.

       This call supersedes readdir(2).

       The original Linux getdents() system call did not handle large
       filesystems and large file offsets.  Consequently, Linux 2.4 added
       getdents64(), with wider types for the d_ino and d_off fields
       employed in the linux_dirent structure.

EXAMPLE         top

       The program below demonstrates the use of getdents().  The following
       output shows an example of what we see when running this program on
       an ext2 directory:

           $ ./a.out /testfs/
           --------------- nread=120 ---------------
           i-node#  file type  d_reclen  d_off   d_name
                  2  directory    16         12  .
                  2  directory    16         24  ..
                 11  directory    24         44  lost+found
                 12  regular      16         56  a
             228929  directory    16         68  sub
              16353  directory    16         80  sub2
             130817  directory    16       4096  sub3

   Program source

       #define _GNU_SOURCE
       #include <dirent.h>     /* Defines DT_* constants */
       #include <fcntl.h>
       #include <stdio.h>
       #include <unistd.h>
       #include <stdlib.h>
       #include <sys/stat.h>
       #include <sys/syscall.h>

       #define handle_error(msg) \
               do { perror(msg); exit(EXIT_FAILURE); } while (0)

       struct linux_dirent {
           long           d_ino;
           off_t          d_off;
           unsigned short d_reclen;
           char           d_name[];
       };

       #define BUF_SIZE 1024

       int
       main(int argc, char *argv[])
       {
           int fd, nread;
           char buf[BUF_SIZE];
           struct linux_dirent *d;
           int bpos;
           char d_type;

           fd = open(argc > 1 ? argv[1] : ".", O_RDONLY | O_DIRECTORY);
           if (fd == -1)
               handle_error("open");

           for ( ; ; ) {
               nread = syscall(SYS_getdents, fd, buf, BUF_SIZE);
               if (nread == -1)
                   handle_error("getdents");

               if (nread == 0)
                   break;

               printf("--------------- nread=%d ---------------\n", nread);
               printf("i-node#  file type  d_reclen  d_off   d_name\n");
               for (bpos = 0; bpos < nread;) {
                   d = (struct linux_dirent *) (buf + bpos);
                   printf("%8ld  ", d->d_ino);
                   d_type = *(buf + bpos + d->d_reclen - 1);
                   printf("%-10s ", (d_type == DT_REG) ?  "regular" :
                                    (d_type == DT_DIR) ?  "directory" :
                                    (d_type == DT_FIFO) ? "FIFO" :
                                    (d_type == DT_SOCK) ? "socket" :
                                    (d_type == DT_LNK) ?  "symlink" :
                                    (d_type == DT_BLK) ?  "block dev" :
                                    (d_type == DT_CHR) ?  "char dev" : "???");
                   printf("%4d %10lld  %s\n", d->d_reclen,
                           (long long) d->d_off, d->d_name);
                   bpos += d->d_reclen;
               }
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

       readdir(2), readdir(3)

COLOPHON         top

       This page is part of release 3.64 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                            2012-08-03                      GETDENTS(2)