/*      $NetBSD: vfs_cwd.c,v 1.12 2024/12/07 02:11:42 riastradh Exp $   */

/*-
 * Copyright (c) 2008, 2020, 2023 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * 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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``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 FOUNDATION OR CONTRIBUTORS
 * 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.
 */

/*
 * Current working directory.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: vfs_cwd.c,v 1.12 2024/12/07 02:11:42 riastradh Exp $");

#include <sys/param.h>

#include <sys/atomic.h>
#include <sys/filedesc.h>
#include <sys/kmem.h>
#include <sys/proc.h>
#include <sys/vnode.h>

/*
 * Create an initial cwdinfo structure, using the same current and root
 * directories as curproc.
 */
struct cwdinfo *
cwdinit(void)
{
        struct cwdinfo *cwdi;
        struct cwdinfo *copy;

        cwdi = kmem_alloc(sizeof(*cwdi), KM_SLEEP);
        KASSERT(ALIGNED_POINTER(cwdi, COHERENCY_UNIT));
        rw_init(&cwdi->cwdi_lock);
        copy = curproc->p_cwdi;

        rw_enter(&copy->cwdi_lock, RW_READER);
        cwdi->cwdi_cdir = copy->cwdi_cdir;
        if (cwdi->cwdi_cdir)
                vref(cwdi->cwdi_cdir);
        cwdi->cwdi_rdir = copy->cwdi_rdir;
        if (cwdi->cwdi_rdir)
                vref(cwdi->cwdi_rdir);
        cwdi->cwdi_edir = copy->cwdi_edir;
        if (cwdi->cwdi_edir)
                vref(cwdi->cwdi_edir);
        rw_exit(&copy->cwdi_lock);

        cwdi->cwdi_cmask = copy->cwdi_cmask;
        cwdi->cwdi_refcnt = 1;

        return cwdi;
}

/*
 * Make p2 share p1's cwdinfo.
 */
void
cwdshare(struct proc *p2)
{
        struct cwdinfo *cwdi;

        cwdi = curproc->p_cwdi;

        atomic_inc_uint(&cwdi->cwdi_refcnt);
        p2->p_cwdi = cwdi;
}

/*
 * Make sure proc has only one reference to its cwdi, creating
 * a new one if necessary.
 */
void
cwdunshare(struct proc *p)
{
        struct cwdinfo *cwdi = p->p_cwdi;

        if (cwdi->cwdi_refcnt > 1) {
                cwdi = cwdinit();
                cwdfree(p->p_cwdi);
                p->p_cwdi = cwdi;
        }
}

/*
 * Release a cwdinfo structure.
 */
void
cwdfree(struct cwdinfo *cwdi)
{

        membar_release();
        if (atomic_dec_uint_nv(&cwdi->cwdi_refcnt) > 0)
                return;
        membar_acquire();

        vrele(cwdi->cwdi_cdir);
        rw_destroy(&cwdi->cwdi_lock);
        if (cwdi->cwdi_rdir)
                vrele(cwdi->cwdi_rdir);
        if (cwdi->cwdi_edir)
                vrele(cwdi->cwdi_edir);
        kmem_free(cwdi, sizeof(*cwdi));
}

void
cwdexec(struct proc *p)
{

        cwdunshare(p);

        if (p->p_cwdi->cwdi_edir) {
                vrele(p->p_cwdi->cwdi_edir);
        }
}