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      1 /*	$NetBSD: vfs_cwd.c,v 1.12 2024/12/07 02:11:42 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2008, 2020, 2023 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * Redistribution and use in source and binary forms, with or without
      8  * modification, are permitted provided that the following conditions
      9  * are met:
     10  * 1. Redistributions of source code must retain the above copyright
     11  *    notice, this list of conditions and the following disclaimer.
     12  * 2. Redistributions in binary form must reproduce the above copyright
     13  *    notice, this list of conditions and the following disclaimer in the
     14  *    documentation and/or other materials provided with the distribution.
     15  *
     16  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     17  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     18  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     19  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     20  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     21  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     22  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     23  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     24  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     25  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     26  * POSSIBILITY OF SUCH DAMAGE.
     27  */
     28 
     29 /*
     30  * Current working directory.
     31  */
     32 
     33 #include <sys/cdefs.h>
     34 __KERNEL_RCSID(0, "$NetBSD: vfs_cwd.c,v 1.12 2024/12/07 02:11:42 riastradh Exp $");
     35 
     36 #include <sys/param.h>
     37 
     38 #include <sys/atomic.h>
     39 #include <sys/filedesc.h>
     40 #include <sys/kmem.h>
     41 #include <sys/proc.h>
     42 #include <sys/vnode.h>
     43 
     44 /*
     45  * Create an initial cwdinfo structure, using the same current and root
     46  * directories as curproc.
     47  */
     48 struct cwdinfo *
     49 cwdinit(void)
     50 {
     51 	struct cwdinfo *cwdi;
     52 	struct cwdinfo *copy;
     53 
     54 	cwdi = kmem_alloc(sizeof(*cwdi), KM_SLEEP);
     55 	KASSERT(ALIGNED_POINTER(cwdi, COHERENCY_UNIT));
     56 	rw_init(&cwdi->cwdi_lock);
     57 	copy = curproc->p_cwdi;
     58 
     59 	rw_enter(&copy->cwdi_lock, RW_READER);
     60 	cwdi->cwdi_cdir = copy->cwdi_cdir;
     61 	if (cwdi->cwdi_cdir)
     62 		vref(cwdi->cwdi_cdir);
     63 	cwdi->cwdi_rdir = copy->cwdi_rdir;
     64 	if (cwdi->cwdi_rdir)
     65 		vref(cwdi->cwdi_rdir);
     66 	cwdi->cwdi_edir = copy->cwdi_edir;
     67 	if (cwdi->cwdi_edir)
     68 		vref(cwdi->cwdi_edir);
     69 	rw_exit(&copy->cwdi_lock);
     70 
     71 	cwdi->cwdi_cmask = copy->cwdi_cmask;
     72 	cwdi->cwdi_refcnt = 1;
     73 
     74 	return cwdi;
     75 }
     76 
     77 /*
     78  * Make p2 share p1's cwdinfo.
     79  */
     80 void
     81 cwdshare(struct proc *p2)
     82 {
     83 	struct cwdinfo *cwdi;
     84 
     85 	cwdi = curproc->p_cwdi;
     86 
     87 	atomic_inc_uint(&cwdi->cwdi_refcnt);
     88 	p2->p_cwdi = cwdi;
     89 }
     90 
     91 /*
     92  * Make sure proc has only one reference to its cwdi, creating
     93  * a new one if necessary.
     94  */
     95 void
     96 cwdunshare(struct proc *p)
     97 {
     98 	struct cwdinfo *cwdi = p->p_cwdi;
     99 
    100 	if (cwdi->cwdi_refcnt > 1) {
    101 		cwdi = cwdinit();
    102 		cwdfree(p->p_cwdi);
    103 		p->p_cwdi = cwdi;
    104 	}
    105 }
    106 
    107 /*
    108  * Release a cwdinfo structure.
    109  */
    110 void
    111 cwdfree(struct cwdinfo *cwdi)
    112 {
    113 
    114 	membar_release();
    115 	if (atomic_dec_uint_nv(&cwdi->cwdi_refcnt) > 0)
    116 		return;
    117 	membar_acquire();
    118 
    119 	vrele(cwdi->cwdi_cdir);
    120 	rw_destroy(&cwdi->cwdi_lock);
    121 	if (cwdi->cwdi_rdir)
    122 		vrele(cwdi->cwdi_rdir);
    123 	if (cwdi->cwdi_edir)
    124 		vrele(cwdi->cwdi_edir);
    125 	kmem_free(cwdi, sizeof(*cwdi));
    126 }
    127 
    128 void
    129 cwdexec(struct proc *p)
    130 {
    131 
    132 	cwdunshare(p);
    133 
    134 	if (p->p_cwdi->cwdi_edir) {
    135 		vrele(p->p_cwdi->cwdi_edir);
    136 	}
    137 }
    138