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NAME

       getdents, getdents64 - get directory entries

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <sys/syscall.h>      /* Definition of SYS_* constants */
       #include <unistd.h>

       long syscall(SYS_getdents, unsigned int fd, struct linux_dirent *dirp,
                    unsigned int count);

       #define _GNU_SOURCE           /* See feature_test_macros(7) */
       #include <dirent.h>

       ssize_t getdents64(int fd, void dirp[.count], size_t count);

       Note: glibc provides no wrapper for getdents(), necessitating the use of syscall(2).

       Note: There is no definition of struct linux_dirent in glibc; see NOTES.

DESCRIPTION

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

   getdents()
       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;     /* Not an offset; see below */
               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 a filesystem-specific value with no specific meaning
       to user space, though on older filesystems it used to be the distance from  the  start  of
       the directory to the start of the next linux_dirent; see readdir(3).  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  up
       to  and including Linux 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.

   getdents64()
       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.  In addition, getdents64() supports an explicit d_type field.

       The getdents64() system call is like getdents(), except that  its  second  argument  is  a
       pointer to a buffer containing structures of the following type:

           struct linux_dirent64 {
               ino64_t        d_ino;    /* 64-bit inode number */
               off64_t        d_off;    /* Not an offset; see getdents() */
               unsigned short d_reclen; /* Size of this dirent */
               unsigned char  d_type;   /* File type */
               char           d_name[]; /* Filename (null-terminated) */
           };

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 to indicate the error.

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.

STANDARDS

       None.

HISTORY

       SVr4.

       getdents64()
              glibc 2.30.

NOTES

       glibc does not provide a wrapper for getdents(); call  getdents()  using  syscall(2).   In
       that case you will need to define the linux_dirent or linux_dirent64 structure yourself.

       Probably, you want to use readdir(3) instead of these system calls.

       These calls supersede readdir(2).

EXAMPLES

       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 ---------------
           inode#    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 <err.h>
       #include <fcntl.h>
       #include <stdint.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/syscall.h>
       #include <sys/types.h>
       #include <unistd.h>

       struct linux_dirent {
           unsigned 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;
           char                 d_type;
           char                 buf[BUF_SIZE];
           long                 nread;
           struct linux_dirent  *d;

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

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

               if (nread == 0)
                   break;

               printf("--------------- nread=%ld ---------------\n", nread);
               printf("inode#    file type  d_reclen  d_off   d_name\n");
               for (size_t bpos = 0; bpos < nread;) {
                   d = (struct linux_dirent *) (buf + bpos);
                   printf("%8lu  ", 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 %10jd  %s\n", d->d_reclen,
                          (intmax_t) d->d_off, d->d_name);
                   bpos += d->d_reclen;
               }
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO

       readdir(2), readdir(3), inode(7)