kern_physio.c revision 1.30 1 /* $NetBSD: kern_physio.c,v 1.30 1998/02/10 14:09:35 mrg 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 "opt_uvm.h"
45
46 #include <sys/param.h>
47 #include <sys/systm.h>
48 #include <sys/buf.h>
49 #include <sys/conf.h>
50 #include <sys/malloc.h>
51 #include <sys/proc.h>
52
53 #include <vm/vm.h>
54
55 #if defined(UVM)
56 #include <uvm/uvm_extern.h>
57 #endif
58
59 /*
60 * The routines implemented in this file are described in:
61 * Leffler, et al.: The Design and Implementation of the 4.3BSD
62 * UNIX Operating System (Addison Welley, 1989)
63 * on pages 231-233.
64 *
65 * The routines "getphysbuf" and "putphysbuf" steal and return a swap
66 * buffer. Leffler, et al., says that swap buffers are used to do the
67 * I/O, so raw I/O requests don't have to be single-threaded.
68 */
69
70 struct buf *getphysbuf __P((void));
71 void putphysbuf __P((struct buf *bp));
72
73 /*
74 * Do "physical I/O" on behalf of a user. "Physical I/O" is I/O directly
75 * from the raw device to user buffers, and bypasses the buffer cache.
76 *
77 * Comments in brackets are from Leffler, et al.'s pseudo-code implementation.
78 */
79 int
80 physio(strategy, bp, dev, flags, minphys, uio)
81 void (*strategy) __P((struct buf *));
82 struct buf *bp;
83 dev_t dev;
84 int flags;
85 void (*minphys) __P((struct buf *));
86 struct uio *uio;
87 {
88 struct iovec *iovp;
89 struct proc *p = curproc;
90 int error, done, i, nobuf, s, todo;
91
92 error = 0;
93 flags &= B_READ | B_WRITE;
94
95 /*
96 * [check user read/write access to the data buffer]
97 *
98 * Check each iov one by one. Note that we know if we're reading or
99 * writing, so we ignore the uio's rw parameter. Also note that if
100 * we're doing a read, that's a *write* to user-space.
101 */
102 if (uio->uio_segflg == UIO_USERSPACE)
103 for (i = 0; i < uio->uio_iovcnt; i++)
104 #if defined(UVM) /* XXXCDC: map not locked, rethink */
105 if (!uvm_useracc(uio->uio_iov[i].iov_base,
106 uio->uio_iov[i].iov_len,
107 (flags == B_READ) ? B_WRITE : B_READ))
108 return (EFAULT);
109 #else
110 if (!useracc(uio->uio_iov[i].iov_base,
111 uio->uio_iov[i].iov_len,
112 (flags == B_READ) ? B_WRITE : B_READ))
113 return (EFAULT);
114 #endif
115
116 /* Make sure we have a buffer, creating one if necessary. */
117 if ((nobuf = (bp == NULL)) != 0) {
118
119 bp = getphysbuf();
120 /* bp was just malloc'd so can't already be busy */
121 bp->b_flags |= B_BUSY;
122
123 } else {
124
125 /* [raise the processor priority level to splbio;] */
126 s = splbio();
127
128 /* [while the buffer is marked busy] */
129 while (bp->b_flags & B_BUSY) {
130 /* [mark the buffer wanted] */
131 bp->b_flags |= B_WANTED;
132 /* [wait until the buffer is available] */
133 tsleep((caddr_t)bp, PRIBIO+1, "physbuf", 0);
134 }
135
136 /* Mark it busy, so nobody else will use it. */
137 bp->b_flags |= B_BUSY;
138
139 /* [lower the priority level] */
140 splx(s);
141
142 }
143
144 /* [set up the fixed part of the buffer for a transfer] */
145 bp->b_dev = dev;
146 bp->b_error = 0;
147 bp->b_proc = p;
148
149 /*
150 * [while there are data to transfer and no I/O error]
151 * Note that I/O errors are handled with a 'goto' at the bottom
152 * of the 'while' loop.
153 */
154 for (i = 0; i < uio->uio_iovcnt; i++) {
155 iovp = &uio->uio_iov[i];
156 while (iovp->iov_len > 0) {
157 /*
158 * [mark the buffer busy for physical I/O]
159 * (i.e. set B_PHYS (because it's an I/O to user
160 * memory, and B_RAW, because B_RAW is to be
161 * "Set by physio for raw transfers.", in addition
162 * to the "busy" and read/write flag.)
163 */
164 bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags;
165
166 /* [set up the buffer for a maximum-sized transfer] */
167 bp->b_blkno = btodb(uio->uio_offset);
168 bp->b_bcount = iovp->iov_len;
169 bp->b_data = iovp->iov_base;
170
171 /*
172 * [call minphys to bound the tranfer size]
173 * and remember the amount of data to transfer,
174 * for later comparison.
175 */
176 (*minphys)(bp);
177 todo = bp->b_bcount;
178 #ifdef DIAGNOSTIC
179 if (todo < 0)
180 panic("todo < 0; minphys broken");
181 if (todo > MAXPHYS)
182 panic("todo > MAXPHYS; minphys broken");
183 #endif
184
185 /*
186 * [lock the part of the user address space involved
187 * in the transfer]
188 * Beware vmapbuf(); it clobbers b_data and
189 * saves it in b_saveaddr. However, vunmapbuf()
190 * restores it.
191 */
192 PHOLD(p);
193 #if defined(UVM)
194 uvm_vslock(bp->b_data, todo);
195 #else
196 vslock(bp->b_data, todo);
197 #endif
198 vmapbuf(bp, todo);
199
200 /* [call strategy to start the transfer] */
201 (*strategy)(bp);
202
203 /*
204 * Note that the raise/wait/lower/get error
205 * steps below would be done by biowait(), but
206 * we want to unlock the address space before
207 * we lower the priority.
208 *
209 * [raise the priority level to splbio]
210 */
211 s = splbio();
212
213 /* [wait for the transfer to complete] */
214 while ((bp->b_flags & B_DONE) == 0)
215 tsleep((caddr_t) bp, PRIBIO + 1, "physio", 0);
216
217 /* Mark it busy again, so nobody else will use it. */
218 bp->b_flags |= B_BUSY;
219
220 /* [lower the priority level] */
221 splx(s);
222
223 /*
224 * [unlock the part of the address space previously
225 * locked]
226 */
227 vunmapbuf(bp, todo);
228 #if defined(UVM)
229 uvm_vsunlock(bp->b_data, todo);
230 #else
231 vsunlock(bp->b_data, todo);
232 #endif
233 PRELE(p);
234
235 /* remember error value (save a splbio/splx pair) */
236 if (bp->b_flags & B_ERROR)
237 error = (bp->b_error ? bp->b_error : EIO);
238
239 /*
240 * [deduct the transfer size from the total number
241 * of data to transfer]
242 */
243 done = bp->b_bcount - bp->b_resid;
244 #ifdef DIAGNOSTIC
245 if (done < 0)
246 panic("done < 0; strategy broken");
247 if (done > todo)
248 panic("done > todo; strategy broken");
249 #endif
250 iovp->iov_len -= done;
251 iovp->iov_base += done;
252 uio->uio_offset += done;
253 uio->uio_resid -= done;
254
255 /*
256 * Now, check for an error.
257 * Also, handle weird end-of-disk semantics.
258 */
259 if (error || done < todo)
260 goto done;
261 }
262 }
263
264 done:
265 /*
266 * [clean up the state of the buffer]
267 * Remember if somebody wants it, so we can wake them up below.
268 * Also, if we had to steal it, give it back.
269 */
270 s = splbio();
271 bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW);
272 if (nobuf)
273 putphysbuf(bp);
274 else {
275 /*
276 * [if another process is waiting for the raw I/O buffer,
277 * wake up processes waiting to do physical I/O;
278 */
279 if (bp->b_flags & B_WANTED) {
280 bp->b_flags &= ~B_WANTED;
281 wakeup(bp);
282 }
283 }
284 splx(s);
285
286 return (error);
287 }
288
289 /*
290 * allocate a buffer structure for use in physical I/O.
291 */
292 struct buf *
293 getphysbuf()
294 {
295 struct buf *bp;
296
297 bp = malloc(sizeof(*bp), M_TEMP, M_WAITOK);
298 bzero(bp, sizeof(*bp));
299
300 /* XXXCDC: are the following two lines necessary? */
301 bp->b_rcred = bp->b_wcred = NOCRED;
302 bp->b_vnbufs.le_next = NOLIST;
303
304 return(bp);
305 }
306
307 /*
308 * get rid of a swap buffer structure which has been used in physical I/O.
309 */
310 void
311 putphysbuf(bp)
312 struct buf *bp;
313 {
314
315 /* XXXCDC: is this necesary? */
316 if (bp->b_vp)
317 brelvp(bp);
318
319 if (bp->b_flags & B_WANTED)
320 panic("putphysbuf: private buf B_WANTED");
321 free(bp, M_TEMP);
322
323 }
324
325 /*
326 * Leffler, et al., says on p. 231:
327 * "The minphys() routine is called by physio() to adjust the
328 * size of each I/O transfer before the latter is passed to
329 * the strategy routine..."
330 *
331 * so, just adjust the buffer's count accounting to MAXPHYS here,
332 * and return the new count;
333 */
334 void
335 minphys(bp)
336 struct buf *bp;
337 {
338
339 if (bp->b_bcount > MAXPHYS)
340 bp->b_bcount = MAXPHYS;
341 }
342