libc/sys/getdirentries.2

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.\"	@(#)getdirentries.2	8.2 (Berkeley) 5/3/95
.\" $FreeBSD: src/lib/libc/sys/getdirentries.2,v 1.12.2.6 2001/12/14 18:34:00 ru Exp $
.\" $DragonFly: src/lib/libc/sys/getdirentries.2,v 1.8 2007/12/23 15:31:28 swildner Exp $
.\"
.Dd July 31, 2006
.Dt GETDIRENTRIES 2
.Os
.Sh NAME
.Nm getdirentries ,
.Nm getdents
.Nd "get directory entries in a filesystem independent format"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In dirent.h
.Ft int
.Fn getdirentries "int fd" "char *buf" "int nbytes" "long *basep"
.Ft int
.Fn getdents "int fd" "char *buf" "int nbytes"
.Ft size_t
.Fn _DIRENT_DIRSIZ "struct dirent *dp"
.Ft struct dirent *
.Fn _DIRENT_NEXT "struct dirent *dp"
.Sh DESCRIPTION
The
.Fn getdirentries
and
.Fn getdents
functions read 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.
The
.Fa nbytes
argument must be greater than or equal to the
block size associated with the file,
see
.Xr stat 2 .
Some filesystems may not support these functions
with buffers smaller than this size.
.Pp
The data in the buffer is a series of
.Em dirent
structures each containing the following entries:
.Bd -literal -offset indent
ino_t     d_fileno;
u_int8_t  d_type;
u_int8_t  d_namlen;
char      d_name[...];	/* 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_type
entry is the type of the file pointed to by the directory record.
The file type values are defined in
.In sys/dirent.h .
The
.Fa d_name
entry contains a null terminated file name.
The
.Fa d_namlen
entry specifies the length of the file name excluding the null byte.
Thus the actual size of
.Fa d_name
may vary from 1 to
.Dv MAXNAMELEN
\&+ 1.
.Pp
Entries may be separated by extra space.
To get the total size of a
.Fa dirent
structure, use the
.Nm _DIRENT_DIRSIZ
macro, or use
.Nm _DIRENT_NEXT
to get a pointer to the following
.Fa dirent
structure.
.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 getdirentries
or
.Fn getdents .
A value of zero is returned when
the end of the directory has been reached.
.Pp
The
.Fn getdirentries
function writes the position of the block read into the location pointed to by
.Fa basep .
Alternatively, 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 ,
a value returned in the location pointed to by
.Fa basep
.Pf ( Fn getdirentries
only)
or zero.
.Sh RETURN VALUES
If successful, the number of bytes actually transferred is returned.
Otherwise, -1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn Getdirentries
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
Either
.Fa buf
or
.Fa basep
point outside the 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
.Tn I/O
error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr lseek 2 ,
.Xr open 2
.Sh HISTORY
The
.Fn getdirentries
function first appeared in
.Bx 4.4 .
The
.Fn getdents
function first appeared in
.Fx 3.0 .
.Sh BUGS
Unfortunately,
.Fa *basep
is only 32 bits wide on 32 bit platforms and
may not be wide enough to accommodate the directory position cookie.
Modern users should use
.Xr lseek 2 .
to retrieve and set the seek position within the directory.
The seek offset is 64 bits wide on all platforms.