1 /* $NetBSD: vfs_cwd.c,v 1.5 2020/02/23 22:14:03 ad Exp $ */ 2 3 /*- 4 * Copyright (c) 2008, 2020 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 1.5 2020/02/23 22:14:03 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/xcall.h> 42 43 static int cwdi_ctor(void *, void *, int); 44 static void cwdi_dtor(void *, void *); 45 46 static pool_cache_t cwdi_cache; 47 48 void 49 cwd_sys_init(void) 50 { 51 52 cwdi_cache = pool_cache_init(sizeof(struct cwdinfo), coherency_unit, 53 0, 0, "cwdi", NULL, IPL_NONE, cwdi_ctor, cwdi_dtor, NULL); 54 KASSERT(cwdi_cache != NULL); 55 } 56 57 /* 58 * Create an initial cwdinfo structure, using the same current and root 59 * directories as curproc. 60 */ 61 struct cwdinfo * 62 cwdinit(void) 63 { 64 struct cwdinfo *cwdi; 65 struct cwdinfo *copy; 66 67 cwdi = pool_cache_get(cwdi_cache, PR_WAITOK); 68 69 copy = cwdenter(RW_READER); 70 cwdi->cwdi_cdir = copy->cwdi_cdir; 71 if (cwdi->cwdi_cdir) 72 vref(cwdi->cwdi_cdir); 73 cwdi->cwdi_rdir = copy->cwdi_rdir; 74 if (cwdi->cwdi_rdir) 75 vref(cwdi->cwdi_rdir); 76 cwdi->cwdi_edir = copy->cwdi_edir; 77 if (cwdi->cwdi_edir) 78 vref(cwdi->cwdi_edir); 79 cwdi->cwdi_cmask = copy->cwdi_cmask; 80 cwdi->cwdi_refcnt = 1; 81 cwdexit(copy); 82 83 return (cwdi); 84 } 85 86 static int 87 cwdi_ctor(void *arg, void *obj, int flags) 88 { 89 struct cwdinfo *cwdi = obj; 90 91 mutex_init(&cwdi->cwdi_lock, MUTEX_DEFAULT, IPL_NONE); 92 93 return 0; 94 } 95 96 static void 97 cwdi_dtor(void *arg, void *obj) 98 { 99 struct cwdinfo *cwdi = obj; 100 101 mutex_destroy(&cwdi->cwdi_lock); 102 } 103 104 /* 105 * Make p2 share p1's cwdinfo. 106 */ 107 void 108 cwdshare(struct proc *p2) 109 { 110 struct cwdinfo *cwdi; 111 112 cwdi = curproc->p_cwdi; 113 114 atomic_inc_uint(&cwdi->cwdi_refcnt); 115 p2->p_cwdi = cwdi; 116 } 117 118 /* 119 * Make sure proc has only one reference to its cwdi, creating 120 * a new one if necessary. 121 */ 122 void 123 cwdunshare(struct proc *p) 124 { 125 struct cwdinfo *cwdi = p->p_cwdi; 126 127 if (cwdi->cwdi_refcnt > 1) { 128 cwdi = cwdinit(); 129 cwdfree(p->p_cwdi); 130 p->p_cwdi = cwdi; 131 } 132 } 133 134 /* 135 * Release a cwdinfo structure. 136 */ 137 void 138 cwdfree(struct cwdinfo *cwdi) 139 { 140 141 if (atomic_dec_uint_nv(&cwdi->cwdi_refcnt) > 0) 142 return; 143 144 vrele(cwdi->cwdi_cdir); 145 if (cwdi->cwdi_rdir) 146 vrele(cwdi->cwdi_rdir); 147 if (cwdi->cwdi_edir) 148 vrele(cwdi->cwdi_edir); 149 pool_cache_put(cwdi_cache, cwdi); 150 } 151 152 void 153 cwdexec(struct proc *p) 154 { 155 156 cwdunshare(p); 157 158 if (p->p_cwdi->cwdi_edir) { 159 vrele(p->p_cwdi->cwdi_edir); 160 } 161 } 162 163 /* 164 * Used when curlwp wants to use or update its cwdinfo, and needs to prevent 165 * concurrent changes. 166 * 167 * "op" is either RW_READER or RW_WRITER indicating the kind of lock 168 * required. If a read lock on the cwdinfo is requested, then curlwp must 169 * not block while holding the lock, or the cwdinfo could become stale. 170 * It's okay to block while holding a write lock. 171 */ 172 struct cwdinfo * 173 cwdenter(krw_t op) 174 { 175 struct cwdinfo *cwdi = curproc->p_cwdi; 176 177 if (__predict_true(op == RW_READER)) { 178 /* 179 * Disable preemption to hold off the writer side's xcall, 180 * then observe the lock. If it's already taken, we need to 181 * join in the melee. Otherwise we're good to go; keeping 182 * the xcall at bay with kpreempt_disable() will prevent any 183 * changes while the caller is pondering the cwdinfo. 184 */ 185 kpreempt_disable(); 186 if (__predict_true(mutex_owner(&cwdi->cwdi_lock) == NULL)) { 187 membar_consumer(); 188 return cwdi; 189 } 190 kpreempt_enable(); 191 mutex_enter(&cwdi->cwdi_lock); 192 } else { 193 /* 194 * About to make changes. If there's more than one 195 * reference on the cwdinfo, or curproc has more than one 196 * LWP, then LWPs other than curlwp can also see the 197 * cwdinfo. Run a cross call to get all LWPs out of the 198 * read section. 199 */ 200 mutex_enter(&cwdi->cwdi_lock); 201 if (cwdi->cwdi_refcnt + curproc->p_nlwps > 2) 202 xc_barrier(0); 203 } 204 return cwdi; 205 } 206 207 /* 208 * Release a lock previously taken with cwdenter(). 209 */ 210 void 211 cwdexit(struct cwdinfo *cwdi) 212 { 213 struct lwp *l = curlwp; 214 215 KASSERT(cwdi == l->l_proc->p_cwdi); 216 217 if (__predict_true(mutex_owner(&cwdi->cwdi_lock) != l)) 218 kpreempt_enable(); 219 else 220 mutex_exit(&cwdi->cwdi_lock); 221 } 222 223 /* 224 * Called when there is a need to inspect some other process' cwdinfo. Used 225 * by procfs and sysctl. This gets you a read lock; the cwdinfo must NOT be 226 * changed. 227 */ 228 const struct cwdinfo * 229 cwdlock(struct proc *p) 230 { 231 struct cwdinfo *cwdi = p->p_cwdi; 232 233 mutex_enter(&cwdi->cwdi_lock); 234 return cwdi; 235 } 236 237 /* 238 * Release a lock acquired with cwdlock(). 239 */ 240 void 241 cwdunlock(struct proc *p) 242 { 243 struct cwdinfo *cwdi = p->p_cwdi; 244 245 mutex_exit(&cwdi->cwdi_lock); 246 } 247 248 /* 249 * Get a reference to the current working directory and return it. 250 */ 251 struct vnode * 252 cwdcdir(void) 253 { 254 struct cwdinfo *cwdi; 255 struct vnode *vp; 256 257 cwdi = cwdenter(RW_READER); 258 if ((vp = cwdi->cwdi_cdir) != NULL) 259 vref(vp); 260 cwdexit(cwdi); 261 return vp; 262 } 263 264 /* 265 * Get a reference to the root directory and return it. 266 */ 267 struct vnode * 268 cwdrdir(void) 269 { 270 struct cwdinfo *cwdi; 271 struct vnode *vp; 272 273 cwdi = cwdenter(RW_READER); 274 if ((vp = cwdi->cwdi_rdir) != NULL) 275 vref(vp); 276 cwdexit(cwdi); 277 return vp; 278 } 279