1.\" -*- nroff -*-
2.\"
3.\" Copyright (c) 1996 Doug Rabson
4.\"
5.\" All rights reserved.
6.\"
7.\" This program is free software.
8.\"
9.\" Redistribution and use in source and binary forms, with or without
10.\" modification, are permitted provided that the following conditions
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12.\" 1. Redistributions of source code must retain the above copyright
13.\" notice, this list of conditions and the following disclaimer.
14.\" 2. Redistributions in binary form must reproduce the above copyright
15.\" notice, this list of conditions and the following disclaimer in the
16.\" documentation and/or other materials provided with the distribution.
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19.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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30.\"
31.Dd July 24, 1996
32.Os
33.Dt VOP_RDWR 9
34.Sh NAME
35.Nm VOP_READ ,
36.Nm VOP_WRITE
37.Nd read or write a file
38.Sh SYNOPSIS
39.Fd #include <sys/param.h>
40.Fd #include <sys/vnode.h>
41.Fd #include <sys/uio.h>
42.Ft int
43.Fn VOP_READ "struct vnode *vp" "struct uio *uio" "int ioflag" "struct ucred *cred"
44.Ft int
45.Fn VOP_WRITE "struct vnode *vp" "struct uio *uio" "int ioflag" "struct ucred *cred"
46.Sh DESCRIPTION
47These entry points read or write the contents of a file
48.Pp
49The arguments are:
50.Bl -tag -width ioflag
51.It Ar vp
52the vnode of the file
53.It Ar uio
54the location of the data to be read or written
55.It Ar ioflag
56various flags
57.It Ar cnp
58the credentials of the caller
59.El
60.Pp
61The
62.Fa ioflag
63argument is used to give directives and hints to the filesystem.
64When attempting a read, the high 16 bits are used to provide a
65read-ahead hint (in units of filesystem blocks) that the filesystem
66should attempt. The low 16 bits are a bit mask which can contain
67the following flags:
68.Bl -tag -width IO_NODELOCKED
69.It Dv IO_UNIT
70do I/O as atomic unit
71.It Dv IO_APPEND
72append write to end
73.It Dv IO_SYNC
74do I/O synchronously
75.It Dv IO_NODELOCKED
76underlying node already locked
77.It Dv IO_NDELAY
78.Dv FNDELAY
79flag set in file table
80.It Dv IO_VMIO
81data already in VMIO space
82.El
83.Sh LOCKS
84The file should be locked on entry and will still be locked on exit.
85.Sh RETURN VALUES
86Zero is returned on success, otherwise an error code is returned.
87.Sh PSEUDOCODE
88.Bd -literal
89int
90vop_read(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
91{
92 struct buf *bp;
93 off_t bytesinfile;
94 daddr_t lbn, nextlbn;
95 long size, xfersize, blkoffset;
96 int error;
97
98 size = block size of filesystem;
99
100 for (error = 0, bp = NULL; uio->uio_resid > 0; bp = NULL) {
101 bytesinfile = size of file - uio->uio_offset;
102 if (bytesinfile <= 0)
103 break;
104
105 lbn = uio->uio_offset / size;
106 blkoffset = uio->uio_offset - lbn * size;
107
108 xfersize = size - blkoffset;
109 if (uio->uio_resid < xfersize)
110 xfersize = uio->uio_resid;
111 if (bytesinfile < xfersize)
112 xfersize = bytesinfile;
113
114 error = bread(vp, lbn, size, NOCRED, &bp);
115 if (error) {
116 brelse(bp);
117 bp = NULL;
118 break;
119 }
120
121 /*
122 * We should only get non-zero b_resid when an I/O error
123 * has occurred, which should cause us to break above.
124 * However, if the short read did not cause an error,
125 * then we want to ensure that we do not uiomove bad
126 * or uninitialized data.
127 */
128 size -= bp->b_resid;
129 if (size < xfersize) {
130 if (size == 0)
131 break;
132 xfersize = size;
133 }
134
135 error = uiomove((char *)bp->b_data + blkoffset, (int)xfersize, uio);
136 if (error)
137 break;
138
139 bqrelse(bp);
140 }
141 if (bp != NULL)
142 bqrelse(bp);
143
144 return error;
145}
146
147int
148vop_write(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
149{
150 struct buf *bp;
151 off_t bytesinfile;
152 daddr_t lbn, nextlbn;
153 off_t osize;
154 long size, resid, xfersize, blkoffset;
155 int flags;
156 int error;
157
158 osize = size of file;
159 size = block size of filesystem;
160 resid = uio->uio_resid;
161 if (ioflag & IO_SYNC)
162 flags = B_SYNC;
163 else
164 flags = 0;
165
166 for (error = 0; uio->uio_resid > 0;) {
167 lbn = uio->uio_offset / size;
168 blkoffset = uio->uio_offset - lbn * size;
169
170 xfersize = size - blkoffset;
171 if (uio->uio_resid < xfersize)
172 xfersize = uio->uio_resid;
173
174 if (uio->uio_offset + xfersize > size of file)
175 vnode_pager_setsize(vp, uio->uio_offset + xfersize);
176
177 if (size > xfersize)
178 flags |= B_CLRBUF;
179 else
180 flags &= ~B_CLRBUF;
181
182 error = find_block_in_file(vp, lbn, blkoffset + xfersize,
183 cred, &bp, flags);
184 if (error)
185 break;
186
187 if (uio->uio_offset + xfersize > size of file)
188 set size of file to uio->uio_offset + xfersize;
189
190 error = uiomove((char *)bp->b_data + blkoffset, (int) xfersize, uio);
191 /* XXX ufs does not check the error here. Why? */
192
193 if (ioflag & IO_VMIO)
194 bp->b_flags |= B_RELBUF; /* ??? */
195
196 if (ioflag & IO_SYNC)
197 bwrite(bp);
198 else if (xfersize + blkoffset == size)
199 bawrite(bp);
200 else
201 bdwrite(bp);
202
203 if (error || xfersize == 0)
204 break;
205 }
206
207 if (error) {
208 if (ioflag & IO_UNIT) {
209 VOP_TRUNCATE(vp, osize, ioflag & IO_SYNC, cred, uio->uio_procp);
210 uio->uio_offset -= resid - uio->uio_resid;
211 uio->uio_resid = resid;
212 }
213 } else if (resid > uio->uio_resid && (ioflag & IO_SYNC)) {
214 struct timeval tv;
215 error = VOP_UPDATE(vp, &tv, &tv, 1); /* XXX what does this do? */
216 }
217
218 return error;
219}
220.Ed
221.Sh ERRORS
222.Bl -tag -width Er
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