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NAME

       getdents - get directory entries

SYNOPSIS

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

DESCRIPTION

       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 file systems (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

       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

       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

       SVr4.

NOTES

       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.

       This call supersedes readdir(2).

       The original Linux getdents() system call did not handle large file systems 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

       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, (char *) d->d_name);
                   bpos += d->d_reclen;
               }
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       readdir(2), readdir(3)

COLOPHON

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       project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
       pages/.