freebsd-dev/share/man/man9/VOP_READDIR.9

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.\" Copyright (c) 1996 Doug Rabson
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.\" $Id: VOP_READDIR.9,v 1.3 1997/03/07 03:32:28 mpp Exp $
.\"
.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 Doug Rabson.