kern_physio.c revision 1.42 1 /* $NetBSD: kern_physio.c,v 1.42 2000/05/08 20:03:20 thorpej 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/malloc.h>
48 #include <sys/proc.h>
49
50 #include <vm/vm.h>
51
52 #include <uvm/uvm_extern.h>
53
54 /*
55 * The routines implemented in this file are described in:
56 * Leffler, et al.: The Design and Implementation of the 4.3BSD
57 * UNIX Operating System (Addison Welley, 1989)
58 * on pages 231-233.
59 *
60 * The routines "getphysbuf" and "putphysbuf" steal and return a swap
61 * buffer. Leffler, et al., says that swap buffers are used to do the
62 * I/O, so raw I/O requests don't have to be single-threaded.
63 */
64
65 struct buf *getphysbuf __P((void));
66 void putphysbuf __P((struct buf *bp));
67
68 /*
69 * Do "physical I/O" on behalf of a user. "Physical I/O" is I/O directly
70 * from the raw device to user buffers, and bypasses the buffer cache.
71 *
72 * Comments in brackets are from Leffler, et al.'s pseudo-code implementation.
73 */
74 int
75 physio(strategy, bp, dev, flags, minphys, uio)
76 void (*strategy) __P((struct buf *));
77 struct buf *bp;
78 dev_t dev;
79 int flags;
80 void (*minphys) __P((struct buf *));
81 struct uio *uio;
82 {
83 struct iovec *iovp;
84 struct proc *p = curproc;
85 int error, done, i, nobuf, s, todo;
86
87 error = 0;
88 flags &= B_READ | B_WRITE | B_ORDERED;
89
90 /*
91 * [check user read/write access to the data buffer]
92 *
93 * Check each iov one by one. Note that we know if we're reading or
94 * writing, so we ignore the uio's rw parameter. Also note that if
95 * we're doing a read, that's a *write* to user-space.
96 */
97 if (uio->uio_segflg == UIO_USERSPACE) {
98 for (i = 0; i < uio->uio_iovcnt; i++) {
99 /* XXXCDC: map not locked, rethink */
100 if (__predict_false(!uvm_useracc(uio->uio_iov[i].iov_base,
101 uio->uio_iov[i].iov_len,
102 (flags == B_READ) ? B_WRITE : B_READ)))
103 return (EFAULT);
104 }
105 }
106
107 /* Make sure we have a buffer, creating one if necessary. */
108 if ((nobuf = (bp == NULL)) != 0) {
109
110 bp = getphysbuf();
111 /* bp was just malloc'd so can't already be busy */
112 bp->b_flags |= B_BUSY;
113
114 } else {
115
116 /* [raise the processor priority level to splbio;] */
117 s = splbio();
118
119 /* [while the buffer is marked busy] */
120 while (bp->b_flags & B_BUSY) {
121 /* [mark the buffer wanted] */
122 bp->b_flags |= B_WANTED;
123 /* [wait until the buffer is available] */
124 tsleep((caddr_t)bp, PRIBIO+1, "physbuf", 0);
125 }
126
127 /* Mark it busy, so nobody else will use it. */
128 bp->b_flags |= B_BUSY;
129
130 /* [lower the priority level] */
131 splx(s);
132
133 }
134
135 /* [set up the fixed part of the buffer for a transfer] */
136 bp->b_dev = dev;
137 bp->b_error = 0;
138 bp->b_proc = p;
139 LIST_INIT(&bp->b_dep);
140
141 /*
142 * [while there are data to transfer and no I/O error]
143 * Note that I/O errors are handled with a 'goto' at the bottom
144 * of the 'while' loop.
145 */
146 for (i = 0; i < uio->uio_iovcnt; i++) {
147 iovp = &uio->uio_iov[i];
148 while (iovp->iov_len > 0) {
149 /*
150 * [mark the buffer busy for physical I/O]
151 * (i.e. set B_PHYS (because it's an I/O to user
152 * memory, and B_RAW, because B_RAW is to be
153 * "Set by physio for raw transfers.", in addition
154 * to the "busy" and read/write flag.)
155 */
156 bp->b_flags = B_BUSY | B_PHYS | B_RAW | flags;
157
158 /* [set up the buffer for a maximum-sized transfer] */
159 bp->b_blkno = btodb(uio->uio_offset);
160 bp->b_bcount = iovp->iov_len;
161 bp->b_data = iovp->iov_base;
162
163 /*
164 * [call minphys to bound the tranfer size]
165 * and remember the amount of data to transfer,
166 * for later comparison.
167 */
168 (*minphys)(bp);
169 todo = bp->b_bcount;
170 #ifdef DIAGNOSTIC
171 if (todo < 0)
172 panic("todo < 0; minphys broken");
173 if (todo > MAXPHYS)
174 panic("todo > MAXPHYS; minphys broken");
175 #endif
176
177 /*
178 * [lock the part of the user address space involved
179 * in the transfer]
180 * Beware vmapbuf(); it clobbers b_data and
181 * saves it in b_saveaddr. However, vunmapbuf()
182 * restores it.
183 */
184 PHOLD(p);
185 if (__predict_false(uvm_vslock(p, bp->b_data, todo,
186 (flags & B_READ) ?
187 VM_PROT_READ | VM_PROT_WRITE : VM_PROT_READ)
188 != KERN_SUCCESS)) {
189 bp->b_flags |= B_ERROR;
190 bp->b_error = EFAULT;
191 goto after_vsunlock;
192 }
193 vmapbuf(bp, todo);
194
195 /* [call strategy to start the transfer] */
196 (*strategy)(bp);
197
198 /*
199 * Note that the raise/wait/lower/get error
200 * steps below would be done by biowait(), but
201 * we want to unlock the address space before
202 * we lower the priority.
203 *
204 * [raise the priority level to splbio]
205 */
206 s = splbio();
207
208 /* [wait for the transfer to complete] */
209 while ((bp->b_flags & B_DONE) == 0)
210 tsleep((caddr_t) bp, PRIBIO + 1, "physio", 0);
211
212 /* Mark it busy again, so nobody else will use it. */
213 bp->b_flags |= B_BUSY;
214
215 /* [lower the priority level] */
216 splx(s);
217
218 /*
219 * [unlock the part of the address space previously
220 * locked]
221 */
222 vunmapbuf(bp, todo);
223 uvm_vsunlock(p, bp->b_data, todo);
224 after_vsunlock:
225 PRELE(p);
226
227 /* remember error value (save a splbio/splx pair) */
228 if (bp->b_flags & B_ERROR)
229 error = (bp->b_error ? bp->b_error : EIO);
230
231 /*
232 * [deduct the transfer size from the total number
233 * of data to transfer]
234 */
235 done = bp->b_bcount - bp->b_resid;
236 #ifdef DIAGNOSTIC
237 if (__predict_false(done < 0))
238 panic("done < 0; strategy broken");
239 if (__predict_false(done > todo))
240 panic("done > todo; strategy broken");
241 #endif
242 iovp->iov_len -= done;
243 iovp->iov_base = (caddr_t)iovp->iov_base + done;
244 uio->uio_offset += done;
245 uio->uio_resid -= done;
246
247 /*
248 * Now, check for an error.
249 * Also, handle weird end-of-disk semantics.
250 */
251 if (error || done < todo)
252 goto done;
253 }
254 }
255
256 done:
257 /*
258 * [clean up the state of the buffer]
259 * Remember if somebody wants it, so we can wake them up below.
260 * Also, if we had to steal it, give it back.
261 */
262 s = splbio();
263 bp->b_flags &= ~(B_BUSY | B_PHYS | B_RAW);
264 if (nobuf)
265 putphysbuf(bp);
266 else {
267 /*
268 * [if another process is waiting for the raw I/O buffer,
269 * wake up processes waiting to do physical I/O;
270 */
271 if (bp->b_flags & B_WANTED) {
272 bp->b_flags &= ~B_WANTED;
273 wakeup(bp);
274 }
275 }
276 splx(s);
277
278 return (error);
279 }
280
281 /*
282 * allocate a buffer structure for use in physical I/O.
283 */
284 struct buf *
285 getphysbuf()
286 {
287 struct buf *bp;
288 int s;
289
290 s = splbio();
291 bp = pool_get(&bufpool, PR_WAITOK);
292 splx(s);
293 memset(bp, 0, sizeof(*bp));
294
295 /* XXXCDC: are the following two lines necessary? */
296 bp->b_rcred = bp->b_wcred = NOCRED;
297 bp->b_vnbufs.le_next = NOLIST;
298
299 return(bp);
300 }
301
302 /*
303 * get rid of a swap buffer structure which has been used in physical I/O.
304 */
305 void
306 putphysbuf(bp)
307 struct buf *bp;
308 {
309 int s;
310
311 /* XXXCDC: is this necesary? */
312 if (bp->b_vp)
313 brelvp(bp);
314
315 if (__predict_false(bp->b_flags & B_WANTED))
316 panic("putphysbuf: private buf B_WANTED");
317 s = splbio();
318 pool_put(&bufpool, bp);
319 splx(s);
320 }
321
322 /*
323 * Leffler, et al., says on p. 231:
324 * "The minphys() routine is called by physio() to adjust the
325 * size of each I/O transfer before the latter is passed to
326 * the strategy routine..."
327 *
328 * so, just adjust the buffer's count accounting to MAXPHYS here,
329 * and return the new count;
330 */
331 void
332 minphys(bp)
333 struct buf *bp;
334 {
335
336 if (bp->b_bcount > MAXPHYS)
337 bp->b_bcount = MAXPHYS;
338 }
339