Annotation of sys/kern/kern_physio.c, Revision 1.1.1.1
1.1 nbrk 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: }
CVSweb
![[BACK]](/icons/back.gif){kind=icon}
Return to kern_physio.c CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / sys / kern