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vfs_cwd.c revision 1.11 
      1 /*	$NetBSD: vfs_cwd.c,v 1.11 2023/09/23 18:21:11 ad 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 1.11 2023/09/23 18:21:11 ad Exp $");
     35 
     36 #include <sys/param.h>
     37 #include <sys/atomic.h>
     38 #include <sys/filedesc.h>
     39 #include <sys/proc.h>
     40 #include <sys/vnode.h>
     41 #include <sys/kmem.h>
     42 
     43 /*
     44  * Create an initial cwdinfo structure, using the same current and root
     45  * directories as curproc.
     46  */
     47 struct cwdinfo *
     48 cwdinit(void)
     49 {
     50 	struct cwdinfo *cwdi;
     51 	struct cwdinfo *copy;
     52 
     53 	cwdi = kmem_alloc(sizeof(*cwdi), KM_SLEEP);
     54 	KASSERT(ALIGNED_POINTER(cwdi, COHERENCY_UNIT));
     55 	rw_init(&cwdi->cwdi_lock);
     56 	copy = curproc->p_cwdi;
     57 
     58 	rw_enter(&copy->cwdi_lock, RW_READER);
     59 	cwdi->cwdi_cdir = copy->cwdi_cdir;
     60 	if (cwdi->cwdi_cdir)
     61 		vref(cwdi->cwdi_cdir);
     62 	cwdi->cwdi_rdir = copy->cwdi_rdir;
     63 	if (cwdi->cwdi_rdir)
     64 		vref(cwdi->cwdi_rdir);
     65 	cwdi->cwdi_edir = copy->cwdi_edir;
     66 	if (cwdi->cwdi_edir)
     67 		vref(cwdi->cwdi_edir);
     68 	rw_exit(&copy->cwdi_lock);
     69 
     70 	cwdi->cwdi_cmask = copy->cwdi_cmask;
     71 	cwdi->cwdi_refcnt = 1;
     72 
     73 	return (cwdi);
     74 }
     75 
     76 /*
     77  * Make p2 share p1's cwdinfo.
     78  */
     79 void
     80 cwdshare(struct proc *p2)
     81 {
     82 	struct cwdinfo *cwdi;
     83 
     84 	cwdi = curproc->p_cwdi;
     85 
     86 	atomic_inc_uint(&cwdi->cwdi_refcnt);
     87 	p2->p_cwdi = cwdi;
     88 }
     89 
     90 /*
     91  * Make sure proc has only one reference to its cwdi, creating
     92  * a new one if necessary.
     93  */
     94 void
     95 cwdunshare(struct proc *p)
     96 {
     97 	struct cwdinfo *cwdi = p->p_cwdi;
     98 
     99 	if (cwdi->cwdi_refcnt > 1) {
    100 		cwdi = cwdinit();
    101 		cwdfree(p->p_cwdi);
    102 		p->p_cwdi = cwdi;
    103 	}
    104 }
    105 
    106 /*
    107  * Release a cwdinfo structure.
    108  */
    109 void
    110 cwdfree(struct cwdinfo *cwdi)
    111 {
    112 
    113 	membar_release();
    114 	if (atomic_dec_uint_nv(&cwdi->cwdi_refcnt) > 0)
    115 		return;
    116 	membar_acquire();
    117 
    118 	vrele(cwdi->cwdi_cdir);
    119 	rw_destroy(&cwdi->cwdi_lock);
    120 	if (cwdi->cwdi_rdir)
    121 		vrele(cwdi->cwdi_rdir);
    122 	if (cwdi->cwdi_edir)
    123 		vrele(cwdi->cwdi_edir);
    124 	kmem_free(cwdi, sizeof(*cwdi));
    125 }
    126 
    127 void
    128 cwdexec(struct proc *p)
    129 {
    130 
    131 	cwdunshare(p);
    132 
    133 	if (p->p_cwdi->cwdi_edir) {
    134 		vrele(p->p_cwdi->cwdi_edir);
    135 	}
    136 }
    137