1 /* $NetBSD: kern_physio.c,v 1.28 1997/05/19 10:43:28 pk Exp $ */ 2 3 /*- 4 * Copyright (c) 1994 Christopher G. Demetriou 5 * Copyright (c) 1982, 1986, 1990, 1993 6 * The Regents of the University of California. All rights reserved. 7 * (c) UNIX System Laboratories, Inc. 8 * All or some portions of this file are derived from material licensed 9 * to the University of California by American Telephone and Telegraph 10 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 11 * the permission of UNIX System Laboratories, Inc. 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 3. All advertising materials mentioning features or use of this software 22 * must display the following acknowledgement: 23 * This product includes software developed by the University of 24 * California, Berkeley and its contributors. 25 * 4. Neither the name of the University nor the names of its contributors 26 * may be used to endorse or promote products derived from this software 27 * without specific prior written permission. 28 * 29 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 30 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 31 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 32 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 33 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 34 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 35 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 36 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 37 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 38 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 39 * SUCH DAMAGE. 40 * 41 * @(#)kern_physio.c 8.1 (Berkeley) 6/10/93 42 */ 43 44 #include <sys/param.h> 45 #include <sys/systm.h> 46 #include <sys/buf.h> 47 #include <sys/conf.h> 48 #include <sys/proc.h> 49 50 #include <vm/vm.h> 51 52 /* 53 * The routines implemented in this file are described in: 54 * Leffler, et al.: The Design and Implementation of the 4.3BSD 55 * UNIX Operating System (Addison Welley, 1989) 56 * on pages 231-233. 57 * 58 * The routines "getphysbuf" and "putphysbuf" steal and return a swap 59 * buffer. Leffler, et al., says that swap buffers are used to do the 60 * I/O, so raw I/O requests don't have to be single-threaded. 61 */ 62 63 struct buf *getphysbuf __P((void)); 64 void putphysbuf __P((struct buf *bp)); 65 66 /* 67 * Do "physical I/O" on behalf of a user. "Physical I/O" is I/O directly 68 * from the raw device to user buffers, and bypasses the buffer cache. 69 * 70 * Comments in brackets are from Leffler, et al.'s pseudo-code implementation. 71 */ 72 int 73 physio(strategy, bp, dev, flags, minphys, uio) 74 void (*strategy) __P((struct buf *)); 75 struct buf *bp; 76 dev_t dev; 77 int flags; 78 void (*minphys) __P((struct buf *)); 79 struct uio *uio; 80 { 81 struct iovec *iovp; 82 struct proc *p = curproc; 83 int error, done, i, nobuf, s, todo; 84 85 error = 0; 86 flags &= B_READ | B_WRITE; 87 88 /* 89 * [check user read/write access to the data buffer] 90 * 91 * Check each iov one by one. Note that we know if we're reading or 92 * writing, so we ignore the uio's rw parameter. Also note that if 93 * we're doing a read, that's a *write* to user-space. 94 */ 95 if (uio->uio_segflg == UIO_USERSPACE) 96 for (i = 0; i < uio->uio_iovcnt; i++) 97 if (!useracc(uio->uio_iov[i].iov_base, 98 uio->uio_iov[i].iov_len, 99 (flags == B_READ) ? B_WRITE : B_READ)) 100 return (EFAULT); 101 102 /* Make sure we have a buffer, creating one if necessary. */ 103 if ((nobuf = (bp == NULL)) != 0) 104 bp = getphysbuf(); 105 106 /* [raise the processor priority level to splbio;] */ 107 s = splbio(); 108 109 /* [while the buffer is marked busy] */ 110 while (bp->b_flags & B_BUSY) { 111 /* [mark the buffer wanted] */ 112 bp->b_flags |= B_WANTED; 113 /* [wait until the buffer is available] */ 114 tsleep((caddr_t)bp, PRIBIO+1, "physbuf", 0); 115 } 116 117 /* Mark it busy, so nobody else will use it. */ 118 bp->b_flags |= B_BUSY; 119 120 /* [lower the priority level] */ 121 splx(s); 122 123 /* [set up the fixed part of the buffer for a transfer] */ 124 bp->b_dev = dev; 125 bp->b_error = 0; 126 bp->b_proc = p; 127 128 /* 129 * [while there are data to transfer and no I/O error] 130 * Note that I/O errors are handled with a 'goto' at the bottom 131 * of the 'while' loop. 132 */ 133 for (i = 0; i < uio->uio_iovcnt; i++) { 134 iovp = &uio->uio_iov[i]; 135 while (iovp->iov_len > 0) { 136 /* 137 * [mark the buffer busy for physical I/O] 138 * (i.e. set B_PHYS (because it's an I/O to user 139 * memory, and B_RAW, because B_RAW is to be 140 * "Set by physio for raw transfers.", in addition 141 * to the "busy" and read/write flag.) 142 */ 143 bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags; 144 145 /* [set up the buffer for a maximum-sized transfer] */ 146 bp->b_blkno = btodb(uio->uio_offset); 147 bp->b_bcount = iovp->iov_len; 148 bp->b_data = iovp->iov_base; 149 150 /* 151 * [call minphys to bound the tranfer size] 152 * and remember the amount of data to transfer, 153 * for later comparison. 154 */ 155 (*minphys)(bp); 156 todo = bp->b_bcount; 157 #ifdef DIAGNOSTIC 158 if (todo < 0) 159 panic("todo < 0; minphys broken"); 160 if (todo > MAXPHYS) 161 panic("todo > MAXPHYS; minphys broken"); 162 #endif 163 164 /* 165 * [lock the part of the user address space involved 166 * in the transfer] 167 * Beware vmapbuf(); it clobbers b_data and 168 * saves it in b_saveaddr. However, vunmapbuf() 169 * restores it. 170 */ 171 PHOLD(p); 172 vslock(bp->b_data, todo); 173 vmapbuf(bp, todo); 174 175 /* [call strategy to start the transfer] */ 176 (*strategy)(bp); 177 178 /* 179 * Note that the raise/wait/lower/get error 180 * steps below would be done by biowait(), but 181 * we want to unlock the address space before 182 * we lower the priority. 183 * 184 * [raise the priority level to splbio] 185 */ 186 s = splbio(); 187 188 /* [wait for the transfer to complete] */ 189 while ((bp->b_flags & B_DONE) == 0) 190 tsleep((caddr_t) bp, PRIBIO + 1, "physio", 0); 191 192 /* Mark it busy again, so nobody else will use it. */ 193 bp->b_flags |= B_BUSY; 194 195 /* [lower the priority level] */ 196 splx(s); 197 198 /* 199 * [unlock the part of the address space previously 200 * locked] 201 */ 202 vunmapbuf(bp, todo); 203 vsunlock(bp->b_data, todo); 204 PRELE(p); 205 206 /* remember error value (save a splbio/splx pair) */ 207 if (bp->b_flags & B_ERROR) 208 error = (bp->b_error ? bp->b_error : EIO); 209 210 /* 211 * [deduct the transfer size from the total number 212 * of data to transfer] 213 */ 214 done = bp->b_bcount - bp->b_resid; 215 #ifdef DIAGNOSTIC 216 if (done < 0) 217 panic("done < 0; strategy broken"); 218 if (done > todo) 219 panic("done > todo; strategy broken"); 220 #endif 221 iovp->iov_len -= done; 222 iovp->iov_base += done; 223 uio->uio_offset += done; 224 uio->uio_resid -= done; 225 226 /* 227 * Now, check for an error. 228 * Also, handle weird end-of-disk semantics. 229 */ 230 if (error || done < todo) 231 goto done; 232 } 233 } 234 235 done: 236 /* 237 * [clean up the state of the buffer] 238 * Remember if somebody wants it, so we can wake them up below. 239 * Also, if we had to steal it, give it back. 240 */ 241 s = splbio(); 242 bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW); 243 if (nobuf) 244 putphysbuf(bp); 245 else { 246 /* 247 * [if another process is waiting for the raw I/O buffer, 248 * wake up processes waiting to do physical I/O; 249 */ 250 if (bp->b_flags & B_WANTED) { 251 bp->b_flags &= ~B_WANTED; 252 wakeup(bp); 253 } 254 } 255 splx(s); 256 257 return (error); 258 } 259 260 /* 261 * Get a swap buffer structure, for use in physical I/O. 262 * Mostly taken from /sys/vm/swap_pager.c, except that it no longer 263 * records buffer list-empty conditions, and sleeps at PRIBIO + 1, 264 * rather than PSWP + 1 (and on a different wchan). 265 */ 266 struct buf * 267 getphysbuf() 268 { 269 struct buf *bp; 270 int s; 271 272 s = splbio(); 273 while (bswlist.b_actf == NULL) { 274 bswlist.b_flags |= B_WANTED; 275 tsleep((caddr_t)&bswlist, PRIBIO + 1, "getphys", 0); 276 } 277 bp = bswlist.b_actf; 278 bswlist.b_actf = bp->b_actf; 279 splx(s); 280 return (bp); 281 } 282 283 /* 284 * Get rid of a swap buffer structure which has been used in physical I/O. 285 * Mostly taken from /sys/vm/swap_pager.c, except that it now uses 286 * wakeup() rather than the VM-internal thread_wakeup(), and that the caller 287 * must mask disk interrupts, rather than putphysbuf() itself. 288 */ 289 void 290 putphysbuf(bp) 291 struct buf *bp; 292 { 293 294 bp->b_actf = bswlist.b_actf; 295 bswlist.b_actf = bp; 296 if (bp->b_vp) 297 brelvp(bp); 298 if (bswlist.b_flags & B_WANTED) { 299 bswlist.b_flags &= ~B_WANTED; 300 wakeup(&bswlist); 301 } 302 } 303 304 /* 305 * Leffler, et al., says on p. 231: 306 * "The minphys() routine is called by physio() to adjust the 307 * size of each I/O transfer before the latter is passed to 308 * the strategy routine..." 309 * 310 * so, just adjust the buffer's count accounting to MAXPHYS here, 311 * and return the new count; 312 */ 313 void 314 minphys(bp) 315 struct buf *bp; 316 { 317 318 if (bp->b_bcount > MAXPHYS) 319 bp->b_bcount = MAXPHYS; 320 } 321