.\"	$OpenBSD: getdents.2,v 1.4 2022/08/04 06:20:24 jsg Exp $
.\"	$NetBSD: getdirentries.2,v 1.7 1995/10/12 15:40:50 jtc Exp $
.\"
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.\"	@(#)getdirentries.2	8.1 (Berkeley) 6/9/93
.\"
.Dd $Mdocdate: August 4 2022 $
.Dt GETDENTS 2
.Os
.Sh NAME
.Nm getdents
.Nd get directory entries in a filesystem independent format
.Sh SYNOPSIS
.In dirent.h
.Ft int
.Fn getdents "int fd" "void *buf" "size_t nbytes"
.Sh DESCRIPTION
.Fn getdents
reads directory entries from the directory
referenced by the file descriptor
.Fa fd
into the buffer pointed to by
.Fa buf ,
in a filesystem independent format.
Up to
.Fa nbytes
of data will be transferred.
.Fa nbytes
must be greater than or equal to the
block size associated with the file (see
.Xr stat 2 ) .
Some filesystems may not support
.Fn getdents
with buffers smaller than this size.
.Pp
The data in the buffer is a series of
.Em dirent
structures each containing at least the following entries:
.Bd -literal -offset indent
ino_t		d_fileno;
off_t		d_off;
u_int16_t	d_reclen;
u_int8_t	d_type;
u_int8_t	d_namlen;
char    	d_name[MAXNAMLEN + 1]; /* see below */
.Ed
.Pp
The
.Fa d_fileno
entry is a number which is unique for each distinct file in the filesystem.
Files that are linked by hard links (see
.Xr link 2 )
have the same
.Fa d_fileno .
The
.Fa d_off
entry is the file offset of the next entry.
The
.Fa d_reclen
entry is the length, in bytes, of the directory record.
.Pp
The
.Fa d_type
is the type of file, where the following are possible types:
.Dv DT_UNKNOWN ,
.Dv DT_FIFO ,
.Dv DT_CHR ,
.Dv DT_DIR ,
.Dv DT_BLK ,
.Dv DT_REG ,
.Dv DT_LNK ,
and
.Dv DT_SOCK .
.Pp
The
.Fa d_namlen
entry specifies the length of the file name excluding the NUL byte.
Thus the actual size of
.Fa d_name
may vary from 1 to
.Dv MAXNAMLEN
\&+ 1.
.Pp
The
.Fa d_name
entry contains a NUL-terminated file name.
.Pp
Entries may be separated by extra space.
The
.Fa d_reclen
entry may be used as an offset from the start of a
.Fa dirent
structure to the next structure, if any.
.Pp
Invalid entries with
.Fa d_fileno
set to 0 may be returned among regular entries.
.Pp
The actual number of bytes transferred is returned.
The current position pointer associated with
.Fa fd
is set to point to the next block of entries.
The pointer may not advance by the number of bytes returned by
.Fn getdents .
.Pp
The current position pointer may be set and retrieved by
.Xr lseek 2 .
The current position pointer should only be set to a value returned by
.Xr lseek 2 ,
the value of
.Fa d_off
from an entry,
or zero.
.Sh RETURN VALUES
If successful, the number of bytes actually transferred is returned.
A value of zero is returned when
the end of the directory has been reached.
Otherwise, \-1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn getdents
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa fd
is not a valid file descriptor open for reading.
.It Bq Er EFAULT
Part of
.Fa buf
points outside the process's allocated address space.
.It Bq Er EINVAL
The file referenced by
.Fa fd
is not a directory, or
.Fa nbytes
is too small for returning a directory entry or block of entries,
or the current position pointer is invalid.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr lseek 2 ,
.Xr open 2 ,
.Xr opendir 3 ,
.Xr dirent 5
.Sh STANDARDS
The
.Fn getdents
call is not a portable interface and should not be used directly by
applications.
Use
.Xr readdir 3
instead.
.Sh HISTORY
The
.Fn getdirentries
function first appeared in
.Bx 4.3 Reno .
In
.Ox 5.5
the
.Fa d_off
entry was added to
.Vt struct dirent
and
.Fn getdirentries
was replaced with
.Fn getdents .