freebsd-nq/share/man/man9/VOP_LINK.9

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.\" Copyright (c) 1996 Doug Rabson
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.Dd July 24, 1996
.Os
.Dt VOP_LINK 9
.Sh NAME
.Nm VOP_LINK
.Nd create a new name for a file
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/vnode.h>
.Ft int
.Fn VOP_LINK "struct vnode *dvp" "struct vnode *vp" "struct componentname *cnp"
.Sh DESCRIPTION
This links a new name in the specified directory to an existing file.
.Pp
Its arguments are:
.Bl -tag -width 8X
.It Ar dvp
the vnode of the directory
.It Ar vp
the vnode of the file to be linked
.It Ar cnp
pathname information about the file
.El
.Pp
The pathname info must be released on exit.  The directory and 
file vnodes should NOT be released on exit.
.Sh LOCKS
The directory,
.Fa dvp
is locked on entry and should remain locked on return.
The file
.Fa vp
is not locked on entry and should remain that way on return.
If your VOP code locks
.Fa vp ,
it must be sure to unlock prior to returning.
.Sh RETURN VALUES
Zero is returned if the file was linked successfully, otherwise an
error is returned.
.Sh PSEUDOCODE
.Bd -literal
int
vop_link(struct vnode *dvp, struct vnode *vp, struct componentname *cnp)
{
    int error = 0;

    if (vp->v_mount != dvp->v_mount) {
	VOP_ABORTOP(dvp, cnp);
	error = EXDEV;
	goto out2;
    }
    if (vp != dvp && (error = VOP_LOCK(vp))) {
	VOP_ABORTOP(dvp, cnp);
	goto out2;
    }

    /*
     * now that we've locked vp, we have to use out1 instead of out2
     */

    if (vp would have too many links) {
	VOP_ABORTOP(dvp, cnp);
	error = EMLINK;
	goto out1;
    }

    if (vp is immutable) {
	VOP_ABORTOP(dvp, cnp);
	error = EPERM;
	goto out1;
    }

    /*
     * Increment link count of vp and write back the on-disc version of it.
     */
    ...;

    if (!error) {
	/*
	 * Add the new name to the directory.
	 */
	...;
    }

    free(cnp->cn_pnbuf, M_NAMEI);
out1:
    if (vp != dvp)
	VOP_UNLOCK(vp);
out2:

    return error;
}
.Ed
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EPERM
the file is immutable
.El
.Sh SEE ALSO
.Xr vnode 9 ,
.Xr vn_lock 9
.Sh AUTHORS
This man page was originally written by
.An Doug Rabson .