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 11.\" are met: 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. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 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, 22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 23.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 27.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28.\" 29.\" $FreeBSD$ 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.In sys/param.h 40.In sys/vnode.h 41.In 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 Fa vp 52the vnode of the file 53.It Fa uio 54the location of the data to be read or written 55.It Fa ioflag 56various flags 57.It Fa cnp 58the credentials of the caller 59.El 60.Pp 61The 62.Fa ioflag 63argument is used to give directives and hints to the file system. 64When attempting a read, the high 16 bits are used to provide a 65read-ahead hint (in units of file system blocks) that the file system 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 file system; 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 file system; 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 223.It Bq Er EFBIG 224An attempt was made to write a file that exceeds the process's file size 225limit or the maximum file size. 226.It Bq Er ENOSPC 227The file system is full. 228.It Bq Er EPERM 229An append-only flag is set on the file, but the caller is attempting to 230write before the current end of file. 231.El 232.Sh SEE ALSO 233.Xr uiomove 9 , 234.Xr vnode 9 235.Sh AUTHORS 236This man page was written by 237.An Doug Rabson . 238