freebsd/share/man/man9/VOP_READDIR.9

.\" -*- nroff -*-
.\"
.\" Copyright (c) 1996 Doug Rabson
.\"
.\" All rights reserved.
.\"
.\" This program is free software.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd July 24, 1996
.Os
.Dt VOP_READDIR 9
.Sh NAME
.Nm VOP_READDIR
.Nd read contents of a directory
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/dirent.h>
.Fd #include <sys/vnode.h>
.Ft int
.Fn VOP_READDIR "struct vnode *vp" "struct uio *uio" "struct ucred *cred" "int *eofflag" "int *ncookies" "u_long **cookies"
.Sh DESCRIPTION
Read directory entries.
.Bl -tag -width ncookies
.It Ar vp
the vnode of the directory
.It Ar uio
where to read the directory contents
.It Ar cred
the caller's credentials
.It Ar eofflag
return end of file status (NULL if not wanted)
.It Ar ncookies
number of directory cookies generated for NFS (NULL if not wanted)
.It Ar cookies
directory seek cookies generated for NFS (NULL if not wanted)
.El
The directory contents are read into
.Dv struct dirent
structures.  If the on-disc data structures differ from this then they
should be translated.
.Sh LOCKS
The directory should be locked on entry and will still be locked on exit.
.Sh RETURN VALUES
Zero is returned on success, otherwise an error code is returned.
.Pp
If this is called from the NFS server, the extra arguments
.Fa eofflag ,
.Fa ncookies
and
.Fa cookies
are given.
The value of
.Fa *eofflag
should be set to TRUE if the end of the directory is reached while
reading.
The directory seek cookies are returned to the NFS client and may be used
later to restart a directory read part way through the directory.
There should be one cookie returned per directory entry.  The value of
the cookie should be the offset within the directory where the on-disc
version of the appropriate directory entry starts.
Memory for the cookies should be allocated using:
.Pp
.Bd -literal
	...;
	*ncookies = number of entries read;
	*cookies = (u_int*)#
		malloc(*ncookies * sizeof(u_int), M_TEMP, M_WAITOK);
.Ed
.Sh PSEUDOCODE
.Bd -literal
int
vop_readdir(struct vnode *vp, struct uio *uio, struct ucred *cred,
	    int *eofflag, int *ncookies, u_int **cookies)
{
    off_t off;
    int error = 0;

    /*
     * Remember the original offset to use later in generating cookies.
     */
    off = uio->uio_offset;

    /*
     * Read directory contents starting at uio->uio_offset into buffer
     * pointed to by uio.
     */
    ...;

    if (!error && ncookies != NULL) {
	struct dirent *dpStart;
	struct dirent *dpEnd;
	struct dirent *dp;
	int count;
	u_int *cookiebuf;
	u_int *cookiep;

	if (uio->uio_segflg != UIO_SYSSPACE || uio->uio_iovcnt != 1)
	    panic("vop_readdir: unexpected uio from NFS server");

	/*
	 * Parse the stuff just read into the uio.
	 */
	dpStart = (struct dirent *)
	    (uio->uio_iov->iov_base - (uio->uio_offset - off));
	dpEnd = (struct dirent *) uio->uio_iov->iov_base;

	/*
	 * Count number of entries.
	 */
	for (dp = dpStart, count = 0;
	     dp < dpEnd;
	     dp = (struct dirent *)((caddr_t) dp + dp->d_reclen))
	    count++;

	cookiebuf = (u_int *) malloc(count * sizeof(u_int), M_TEMP, M_WAITOK);
	for (dp = dpStart; cookiep = cookiebuf;
	     dp < dpEnd;
	     dp = (struct dirent *)((caddr_t) dp + dp->d_reclen)) {
	    off += dp->d_reclen;
	    *cookiep++ = (u_int) off;
	}
	*ncookies = count;
	*cookies = cookiebuf;
    }

    if (eofflag && uio->uio_offset is past the end of the directory) {
	*eofflag = TRUE;
    }

    return error;
}
.Ed
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EINVAL
attempt to read from an illegal offset in the directory
.It Bq Er EIO
a read error occurred while reading the directory
.El
.Sh SEE ALSO
.Xr vnode 9
.Sh AUTHORS
This man page was written by
.An Doug Rabson .