1 /* $OpenBSD: kern_physio.c,v 1.28 2007/05/26 20:26:51 pedro Exp $ */ 2 /* $NetBSD: kern_physio.c,v 1.28 1997/05/19 10:43:28 pk Exp $ */ 3 4 /*- 5 * Copyright (c) 1994 Christopher G. Demetriou 6 * Copyright (c) 1982, 1986, 1990, 1993 7 * The Regents of the University of California. All rights reserved. 8 * (c) UNIX System Laboratories, Inc. 9 * All or some portions of this file are derived from material licensed 10 * to the University of California by American Telephone and Telegraph 11 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 12 * the permission of UNIX System Laboratories, Inc. 13 * 14 * Redistribution and use in source and binary forms, with or without 15 * modification, are permitted provided that the following conditions 16 * are met: 17 * 1. Redistributions of source code must retain the above copyright 18 * notice, this list of conditions and the following disclaimer. 19 * 2. Redistributions in binary form must reproduce the above copyright 20 * notice, this list of conditions and the following disclaimer in the 21 * documentation and/or other materials provided with the distribution. 22 * 3. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)kern_physio.c 8.1 (Berkeley) 6/10/93 39 */ 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/buf.h> 44 #include <sys/conf.h> 45 #include <sys/proc.h> 46 #include <sys/pool.h> 47 48 #include <uvm/uvm_extern.h> 49 50 /* 51 * The routines implemented in this file are described in: 52 * Leffler, et al.: The Design and Implementation of the 4.3BSD 53 * UNIX Operating System (Addison Welley, 1989) 54 * on pages 231-233. 55 * 56 * The routines "getphysbuf" and "putphysbuf" steal and return a swap 57 * buffer. Leffler, et al., says that swap buffers are used to do the 58 * I/O, so raw I/O requests don't have to be single-threaded. 59 */ 60 61 struct buf *getphysbuf(void); 62 void putphysbuf(struct buf *bp); 63 64 /* 65 * Do "physical I/O" on behalf of a user. "Physical I/O" is I/O directly 66 * from the raw device to user buffers, and bypasses the buffer cache. 67 * 68 * Comments in brackets are from Leffler, et al.'s pseudo-code implementation. 69 */ 70 int 71 physio(void (*strategy)(struct buf *), struct buf *bp, dev_t dev, int flags, 72 void (*minphys)(struct buf *), struct uio *uio) 73 { 74 struct iovec *iovp; 75 struct proc *p = curproc; 76 int error, done, i, nobuf, s, todo; 77 78 error = 0; 79 flags &= B_READ | B_WRITE; 80 81 /* Make sure we have a buffer, creating one if necessary. */ 82 if ((nobuf = (bp == NULL)) != 0) 83 bp = getphysbuf(); 84 85 /* [raise the processor priority level to splbio;] */ 86 s = splbio(); 87 88 /* [while the buffer is marked busy] */ 89 while (bp->b_flags & B_BUSY) { 90 /* [mark the buffer wanted] */ 91 bp->b_flags |= B_WANTED; 92 /* [wait until the buffer is available] */ 93 tsleep(bp, PRIBIO+1, "physbuf", 0); 94 } 95 96 /* Mark it busy, so nobody else will use it. */ 97 bp->b_flags |= B_BUSY; 98 99 /* [lower the priority level] */ 100 splx(s); 101 102 /* [set up the fixed part of the buffer for a transfer] */ 103 bp->b_dev = dev; 104 bp->b_error = 0; 105 bp->b_proc = p; 106 LIST_INIT(&bp->b_dep); 107 108 /* 109 * [while there are data to transfer and no I/O error] 110 * Note that I/O errors are handled with a 'goto' at the bottom 111 * of the 'while' loop. 112 */ 113 for (i = 0; i < uio->uio_iovcnt; i++) { 114 iovp = &uio->uio_iov[i]; 115 while (iovp->iov_len > 0) { 116 /* 117 * [mark the buffer busy for physical I/O] 118 * (i.e. set B_PHYS (because it's an I/O to user 119 * memory), and B_RAW, because B_RAW is to be 120 * "Set by physio for raw transfers.", in addition 121 * to the "busy" and read/write flag.) 122 */ 123 bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags; 124 125 /* [set up the buffer for a maximum-sized transfer] */ 126 bp->b_blkno = btodb(uio->uio_offset); 127 bp->b_data = iovp->iov_base; 128 129 /* 130 * Because iov_len is unsigned but b_bcount is signed, 131 * an overflow is possible. Therefore bound to MAXPHYS 132 * before calling minphys. 133 */ 134 if (iovp->iov_len > MAXPHYS) 135 bp->b_bcount = MAXPHYS; 136 else 137 bp->b_bcount = iovp->iov_len; 138 139 /* 140 * [call minphys to bound the transfer size] 141 * and remember the amount of data to transfer, 142 * for later comparison. 143 */ 144 (*minphys)(bp); 145 todo = bp->b_bcount; 146 #ifdef DIAGNOSTIC 147 if (todo < 0) 148 panic("todo < 0; minphys broken"); 149 if (todo > MAXPHYS) 150 panic("todo > MAXPHYS; minphys broken"); 151 #endif 152 153 /* 154 * [lock the part of the user address space involved 155 * in the transfer] 156 * Beware vmapbuf(); it clobbers b_data and 157 * saves it in b_saveaddr. However, vunmapbuf() 158 * restores it. 159 */ 160 error = uvm_vslock(p, bp->b_data, todo, 161 (flags & B_READ) ? 162 VM_PROT_READ | VM_PROT_WRITE : VM_PROT_READ); 163 if (error) { 164 bp->b_flags |= B_ERROR; 165 bp->b_error = error; 166 goto after_unlock; 167 } 168 vmapbuf(bp, todo); 169 170 /* [call strategy to start the transfer] */ 171 (*strategy)(bp); 172 173 /* 174 * Note that the raise/wait/lower/get error 175 * steps below would be done by biowait(), but 176 * we want to unlock the address space before 177 * we lower the priority. 178 * 179 * [raise the priority level to splbio] 180 */ 181 s = splbio(); 182 183 /* [wait for the transfer to complete] */ 184 while ((bp->b_flags & B_DONE) == 0) 185 tsleep(bp, PRIBIO + 1, "physio", 0); 186 187 /* Mark it busy again, so nobody else will use it. */ 188 bp->b_flags |= B_BUSY; 189 190 /* [lower the priority level] */ 191 splx(s); 192 193 /* 194 * [unlock the part of the address space previously 195 * locked] 196 */ 197 vunmapbuf(bp, todo); 198 uvm_vsunlock(p, bp->b_data, todo); 199 after_unlock: 200 201 /* remember error value (save a splbio/splx pair) */ 202 if (bp->b_flags & B_ERROR) 203 error = (bp->b_error ? bp->b_error : EIO); 204 205 /* 206 * [deduct the transfer size from the total number 207 * of data to transfer] 208 */ 209 done = bp->b_bcount - bp->b_resid; 210 #ifdef DIAGNOSTIC 211 if (done < 0) 212 panic("done < 0; strategy broken"); 213 if (done > todo) 214 panic("done > todo; strategy broken"); 215 #endif 216 iovp->iov_len -= done; 217 iovp->iov_base = (caddr_t)iovp->iov_base + done; 218 uio->uio_offset += done; 219 uio->uio_resid -= done; 220 221 /* 222 * Now, check for an error. 223 * Also, handle weird end-of-disk semantics. 224 */ 225 if (error || done < todo) 226 goto done; 227 } 228 } 229 230 done: 231 /* 232 * [clean up the state of the buffer] 233 * Remember if somebody wants it, so we can wake them up below. 234 * Also, if we had to steal it, give it back. 235 */ 236 s = splbio(); 237 bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW); 238 if (nobuf) 239 putphysbuf(bp); 240 else { 241 /* 242 * [if another process is waiting for the raw I/O buffer, 243 * wake up processes waiting to do physical I/O] 244 */ 245 if (bp->b_flags & B_WANTED) { 246 bp->b_flags &= ~B_WANTED; 247 wakeup(bp); 248 } 249 } 250 splx(s); 251 252 return (error); 253 } 254 255 /* 256 * Get a swap buffer structure, for use in physical I/O. 257 * Mostly taken from /sys/vm/swap_pager.c, except that it no longer 258 * records buffer list-empty conditions, and sleeps at PRIBIO + 1, 259 * rather than PSWP + 1 (and on a different wchan). 260 */ 261 struct buf * 262 getphysbuf(void) 263 { 264 struct buf *bp; 265 int s; 266 267 s = splbio(); 268 bp = pool_get(&bufpool, PR_WAITOK); 269 splx(s); 270 271 bzero(bp, sizeof(*bp)); 272 273 /* XXXCDC: are the following two lines necessary? */ 274 bp->b_vnbufs.le_next = NOLIST; 275 276 return (bp); 277 } 278 279 /* 280 * Get rid of a swap buffer structure which has been used in physical I/O. 281 * Mostly taken from /sys/vm/swap_pager.c, except that it now uses 282 * wakeup() rather than the VM-internal thread_wakeup(), and that the caller 283 * must mask disk interrupts, rather than putphysbuf() itself. 284 */ 285 void 286 putphysbuf(struct buf *bp) 287 { 288 splassert(IPL_BIO); 289 290 /* XXXCDC: is this necessary? */ 291 if (bp->b_vp) 292 brelvp(bp); 293 294 #ifdef DIAGNOSTIC 295 if (bp->b_flags & B_WANTED) 296 panic("putphysbuf: private buf B_WANTED"); 297 #endif 298 pool_put(&bufpool, bp); 299 } 300 301 /* 302 * Leffler, et al., says on p. 231: 303 * "The minphys() routine is called by physio() to adjust the 304 * size of each I/O transfer before the latter is passed to 305 * the strategy routine..." 306 * 307 * so, just adjust the buffer's count accounting to MAXPHYS here, 308 * and return the new count; 309 */ 310 void 311 minphys(struct buf *bp) 312 { 313 314 if (bp->b_bcount > MAXPHYS) 315 bp->b_bcount = MAXPHYS; 316 } 317