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 *
cwdinit(void)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(©->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(©->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
cwdshare(struct proc * p2)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
cwdunshare(struct proc * p)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
cwdfree(struct cwdinfo * cwdi)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
cwdexec(struct proc * p)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