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       getdents, getdents64 - get directory entries


       Standard C library (libc, -lc)


       #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.


       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

       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 up
       to and including Linux 2.6.3, attempting to access this field always provides the value  0

       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.

       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;    /* 64-bit offset to next structure */
               unsigned short d_reclen; /* Size of this dirent */
               unsigned char  d_type;   /* File type */
               char           d_name[]; /* Filename (null-terminated) */


       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.


       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.

              File descriptor does not refer to a directory.




       Library support for getdents64() was added in glibc 2.30; glibc does not provide a wrapper
       for getdents();  call  getdents()  (or  getdents64()  on  earlier  glibc  versions)  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).


       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 <unistd.h>

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

       #define BUF_SIZE 1024

       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)

               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;



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