Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_physio.c
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1 /* $NetBSD: kern_physio.c,v 1.60 2004/03/23 13:22:33 junyoung Exp $ */ 2 3 /*- 4 * Copyright (c) 1982, 1986, 1990, 1993 5 * The Regents of the University of California. All rights reserved. 6 * (c) UNIX System Laboratories, Inc. 7 * All or some portions of this file are derived from material licensed 8 * to the University of California by American Telephone and Telegraph 9 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 10 * the permission of UNIX System Laboratories, Inc. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 * 36 * @(#)kern_physio.c 8.1 (Berkeley) 6/10/93 37 */ 38 39 /*- 40 * Copyright (c) 1994 Christopher G. Demetriou 41 * 42 * Redistribution and use in source and binary forms, with or without 43 * modification, are permitted provided that the following conditions 44 * are met: 45 * 1. Redistributions of source code must retain the above copyright 46 * notice, this list of conditions and the following disclaimer. 47 * 2. Redistributions in binary form must reproduce the above copyright 48 * notice, this list of conditions and the following disclaimer in the 49 * documentation and/or other materials provided with the distribution. 50 * 3. All advertising materials mentioning features or use of this software 51 * must display the following acknowledgement: 52 * This product includes software developed by the University of 53 * California, Berkeley and its contributors. 54 * 4. Neither the name of the University nor the names of its contributors 55 * may be used to endorse or promote products derived from this software 56 * without specific prior written permission. 57 * 58 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 59 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 60 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 61 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 62 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 63 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 64 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 65 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 66 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 67 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 68 * SUCH DAMAGE. 69 * 70 * @(#)kern_physio.c 8.1 (Berkeley) 6/10/93 71 */ 72 73 #include <sys/cdefs.h> 74 __KERNEL_RCSID(0, "$NetBSD: kern_physio.c,v 1.60 2004/03/23 13:22:33 junyoung Exp $"); 75 76 #include <sys/param.h> 77 #include <sys/systm.h> 78 #include <sys/buf.h> 79 #include <sys/malloc.h> 80 #include <sys/proc.h> 81 82 #include <uvm/uvm_extern.h> 83 84 /* 85 * The routines implemented in this file are described in: 86 * Leffler, et al.: The Design and Implementation of the 4.3BSD 87 * UNIX Operating System (Addison Welley, 1989) 88 * on pages 231-233. 89 * 90 * The routines "getphysbuf" and "putphysbuf" steal and return a swap 91 * buffer. Leffler, et al., says that swap buffers are used to do the 92 * I/O, so raw I/O requests don't have to be single-threaded. 93 */ 94 95 struct buf *getphysbuf(void); 96 void putphysbuf(struct buf *bp); 97 98 /* 99 * Do "physical I/O" on behalf of a user. "Physical I/O" is I/O directly 100 * from the raw device to user buffers, and bypasses the buffer cache. 101 * 102 * Comments in brackets are from Leffler, et al.'s pseudo-code implementation. 103 */ 104 int 105 physio(strategy, bp, dev, flags, min_phys, uio) 106 void (*strategy)(struct buf *); 107 struct buf *bp; 108 dev_t dev; 109 int flags; 110 void (*min_phys)(struct buf *); 111 struct uio *uio; 112 { 113 struct iovec *iovp; 114 struct lwp *l = curlwp; 115 struct proc *p = l->l_proc; 116 int error, done, i, nobuf, s; 117 long todo; 118 119 error = 0; 120 flags &= B_READ | B_WRITE; 121 122 /* Make sure we have a buffer, creating one if necessary. */ 123 if ((nobuf = (bp == NULL)) != 0) { 124 125 bp = getphysbuf(); 126 /* bp was just malloc'd so can't already be busy */ 127 bp->b_flags |= B_BUSY; 128 129 } else { 130 131 /* [raise the processor priority level to splbio;] */ 132 s = splbio(); 133 134 /* [while the buffer is marked busy] */ 135 while (bp->b_flags & B_BUSY) { 136 /* [mark the buffer wanted] */ 137 bp->b_flags |= B_WANTED; 138 /* [wait until the buffer is available] */ 139 tsleep((caddr_t)bp, PRIBIO+1, "physbuf", 0); 140 } 141 142 /* Mark it busy, so nobody else will use it. */ 143 bp->b_flags |= B_BUSY; 144 145 /* [lower the priority level] */ 146 splx(s); 147 } 148 149 /* [set up the fixed part of the buffer for a transfer] */ 150 bp->b_dev = dev; 151 bp->b_error = 0; 152 bp->b_proc = p; 153 LIST_INIT(&bp->b_dep); 154 155 /* 156 * [while there are data to transfer and no I/O error] 157 * Note that I/O errors are handled with a 'goto' at the bottom 158 * of the 'while' loop. 159 */ 160 for (i = 0; i < uio->uio_iovcnt; i++) { 161 iovp = &uio->uio_iov[i]; 162 while (iovp->iov_len > 0) { 163 164 /* 165 * [mark the buffer busy for physical I/O] 166 * (i.e. set B_PHYS (because it's an I/O to user 167 * memory, and B_RAW, because B_RAW is to be 168 * "Set by physio for raw transfers.", in addition 169 * to the "busy" and read/write flag.) 170 */ 171 bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags; 172 173 /* [set up the buffer for a maximum-sized transfer] */ 174 bp->b_blkno = btodb(uio->uio_offset); 175 bp->b_bcount = iovp->iov_len; 176 bp->b_data = iovp->iov_base; 177 178 /* 179 * [call minphys to bound the transfer size] 180 * and remember the amount of data to transfer, 181 * for later comparison. 182 */ 183 (*min_phys)(bp); 184 todo = bp->b_bcount; 185 #ifdef DIAGNOSTIC 186 if (todo <= 0) 187 panic("todo(%ld) <= 0; minphys broken", todo); 188 if (todo > MAXPHYS) 189 panic("todo(%ld) > MAXPHYS; minphys broken", 190 todo); 191 #endif 192 193 /* 194 * [lock the part of the user address space involved 195 * in the transfer] 196 * Beware vmapbuf(); it clobbers b_data and 197 * saves it in b_saveaddr. However, vunmapbuf() 198 * restores it. 199 */ 200 PHOLD(l); 201 error = uvm_vslock(p, bp->b_data, todo, 202 (flags & B_READ) ? 203 VM_PROT_WRITE : VM_PROT_READ); 204 if (error) { 205 bp->b_flags |= B_ERROR; 206 bp->b_error = error; 207 goto after_vsunlock; 208 } 209 vmapbuf(bp, todo); 210 211 BIO_SETPRIO(bp, BPRIO_TIMECRITICAL); 212 213 /* [call strategy to start the transfer] */ 214 (*strategy)(bp); 215 216 /* 217 * Note that the raise/wait/lower/get error 218 * steps below would be done by biowait(), but 219 * we want to unlock the address space before 220 * we lower the priority. 221 * 222 * [raise the priority level to splbio] 223 */ 224 s = splbio(); 225 226 /* [wait for the transfer to complete] */ 227 while ((bp->b_flags & B_DONE) == 0) 228 tsleep((caddr_t) bp, PRIBIO + 1, "physio", 0); 229 230 /* Mark it busy again, so nobody else will use it. */ 231 bp->b_flags |= B_BUSY; 232 233 /* [lower the priority level] */ 234 splx(s); 235 236 /* 237 * [unlock the part of the address space previously 238 * locked] 239 */ 240 vunmapbuf(bp, todo); 241 uvm_vsunlock(p, bp->b_data, todo); 242 after_vsunlock: 243 PRELE(l); 244 245 /* remember error value (save a splbio/splx pair) */ 246 if (bp->b_flags & B_ERROR) 247 error = (bp->b_error ? bp->b_error : EIO); 248 249 /* 250 * [deduct the transfer size from the total number 251 * of data to transfer] 252 */ 253 done = bp->b_bcount - bp->b_resid; 254 KASSERT(done >= 0); 255 KASSERT(done <= todo); 256 257 iovp->iov_len -= done; 258 iovp->iov_base = (caddr_t)iovp->iov_base + done; 259 uio->uio_offset += done; 260 uio->uio_resid -= done; 261 262 /* 263 * Now, check for an error. 264 * Also, handle weird end-of-disk semantics. 265 */ 266 if (error || done < todo) 267 goto done; 268 } 269 } 270 271 done: 272 /* 273 * [clean up the state of the buffer] 274 * Remember if somebody wants it, so we can wake them up below. 275 * Also, if we had to steal it, give it back. 276 */ 277 s = splbio(); 278 bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW); 279 if (nobuf) 280 putphysbuf(bp); 281 else { 282 /* 283 * [if another process is waiting for the raw I/O buffer, 284 * wake up processes waiting to do physical I/O; 285 */ 286 if (bp->b_flags & B_WANTED) { 287 bp->b_flags &= ~B_WANTED; 288 wakeup(bp); 289 } 290 } 291 splx(s); 292 293 return (error); 294 } 295 296 /* 297 * allocate a buffer structure for use in physical I/O. 298 */ 299 struct buf * 300 getphysbuf() 301 { 302 struct buf *bp; 303 int s; 304 305 s = splbio(); 306 bp = pool_get(&bufpool, PR_WAITOK); 307 splx(s); 308 memset(bp, 0, sizeof(*bp)); 309 BUF_INIT(bp); 310 return(bp); 311 } 312 313 /* 314 * get rid of a swap buffer structure which has been used in physical I/O. 315 */ 316 void 317 putphysbuf(bp) 318 struct buf *bp; 319 { 320 int s; 321 322 if (__predict_false(bp->b_flags & B_WANTED)) 323 panic("putphysbuf: private buf B_WANTED"); 324 s = splbio(); 325 pool_put(&bufpool, bp); 326 splx(s); 327 } 328 329 /* 330 * Leffler, et al., says on p. 231: 331 * "The minphys() routine is called by physio() to adjust the 332 * size of each I/O transfer before the latter is passed to 333 * the strategy routine..." 334 * 335 * so, just adjust the buffer's count accounting to MAXPHYS here, 336 * and return the new count; 337 */ 338 void 339 minphys(bp) 340 struct buf *bp; 341 { 342 343 if (bp->b_bcount > MAXPHYS) 344 bp->b_bcount = MAXPHYS; 345 }
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