240 lines
6.2 KiB
Groff
240 lines
6.2 KiB
Groff
.\" -*- nroff -*-
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.\"
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.\" Copyright (c) 1996 Doug Rabson
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.\"
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.\" All rights reserved.
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.\"
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.\" This program is free software.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 24, 1996
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.Os
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.Dt VOP_RDWR 9
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.Sh NAME
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.Nm VOP_READ ,
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.Nm VOP_WRITE
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.Nd read or write a file
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/vnode.h
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.In sys/uio.h
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.Ft int
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.Fn VOP_READ "struct vnode *vp" "struct uio *uio" "int ioflag" "struct ucred *cred"
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.Ft int
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.Fn VOP_WRITE "struct vnode *vp" "struct uio *uio" "int ioflag" "struct ucred *cred"
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.Sh DESCRIPTION
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These entry points read or write the contents of a file
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.Pp
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The arguments are:
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.Bl -tag -width ioflag
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.It Fa vp
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The vnode of the file.
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.It Fa uio
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The location of the data to be read or written.
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.It Fa ioflag
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Various flags.
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.It Fa cnp
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The credentials of the caller.
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.El
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.Pp
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The
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.Fa ioflag
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argument is used to give directives and hints to the file system.
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When attempting a read, the high 16 bits are used to provide a
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read-ahead hint (in units of file system blocks) that the file system
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should attempt.
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The low 16 bits are a bit mask which can contain
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the following flags:
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.Bl -tag -width ".Dv IO_NODELOCKED"
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.It Dv IO_UNIT
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Do I/O as atomic unit.
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.It Dv IO_APPEND
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Append write to end.
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.It Dv IO_SYNC
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Do I/O synchronously.
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.It Dv IO_NODELOCKED
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Underlying node already locked.
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.It Dv IO_NDELAY
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.Dv FNDELAY
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flag set in file table.
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.It Dv IO_VMIO
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Data already in VMIO space.
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.El
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.Sh LOCKS
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The file should be locked on entry and will still be locked on exit.
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.Sh RETURN VALUES
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Zero is returned on success, otherwise an error code is returned.
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.Sh PSEUDOCODE
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.Bd -literal
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int
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vop_read(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
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{
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struct buf *bp;
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off_t bytesinfile;
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daddr_t lbn, nextlbn;
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long size, xfersize, blkoffset;
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int error;
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size = block size of file system;
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for (error = 0, bp = NULL; uio->uio_resid > 0; bp = NULL) {
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bytesinfile = size of file - uio->uio_offset;
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if (bytesinfile <= 0)
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break;
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lbn = uio->uio_offset / size;
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blkoffset = uio->uio_offset - lbn * size;
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xfersize = size - blkoffset;
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if (uio->uio_resid < xfersize)
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xfersize = uio->uio_resid;
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if (bytesinfile < xfersize)
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xfersize = bytesinfile;
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error = bread(vp, lbn, size, NOCRED, &bp);
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if (error) {
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brelse(bp);
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bp = NULL;
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break;
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}
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/*
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* We should only get non-zero b_resid when an I/O error
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* has occurred, which should cause us to break above.
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* However, if the short read did not cause an error,
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* then we want to ensure that we do not uiomove bad
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* or uninitialized data.
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*/
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size -= bp->b_resid;
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if (size < xfersize) {
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if (size == 0)
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break;
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xfersize = size;
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}
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error = uiomove((char *)bp->b_data + blkoffset, (int)xfersize, uio);
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if (error)
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break;
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bqrelse(bp);
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}
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if (bp != NULL)
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bqrelse(bp);
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return (error);
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}
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int
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vop_write(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
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{
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struct buf *bp;
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off_t bytesinfile;
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daddr_t lbn, nextlbn;
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off_t osize;
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long size, resid, xfersize, blkoffset;
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int flags;
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int error;
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osize = size of file;
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size = block size of file system;
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resid = uio->uio_resid;
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if (ioflag & IO_SYNC)
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flags = B_SYNC;
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else
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flags = 0;
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for (error = 0; uio->uio_resid > 0;) {
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lbn = uio->uio_offset / size;
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blkoffset = uio->uio_offset - lbn * size;
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xfersize = size - blkoffset;
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if (uio->uio_resid < xfersize)
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xfersize = uio->uio_resid;
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if (uio->uio_offset + xfersize > size of file)
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vnode_pager_setsize(vp, uio->uio_offset + xfersize);
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if (size > xfersize)
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flags |= B_CLRBUF;
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else
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flags &= ~B_CLRBUF;
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error = find_block_in_file(vp, lbn, blkoffset + xfersize,
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cred, &bp, flags);
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if (error)
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break;
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if (uio->uio_offset + xfersize > size of file)
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set size of file to uio->uio_offset + xfersize;
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error = uiomove((char *)bp->b_data + blkoffset, (int) xfersize, uio);
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/* XXX ufs does not check the error here. Why? */
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if (ioflag & IO_VMIO)
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bp->b_flags |= B_RELBUF; /* ??? */
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if (ioflag & IO_SYNC)
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bwrite(bp);
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else if (xfersize + blkoffset == size)
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bawrite(bp);
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else
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bdwrite(bp);
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if (error || xfersize == 0)
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break;
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}
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if (error) {
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if (ioflag & IO_UNIT) {
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/* call private routine to truncate file. */
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your_truncate(vp, osize, ioflag & IO_SYNC, cred, uio->uio_td);
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uio->uio_offset -= resid - uio->uio_resid;
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uio->uio_resid = resid;
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}
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} else if (resid > uio->uio_resid && (ioflag & IO_SYNC)) {
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struct timeval tv;
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error = VOP_UPDATE(vp, &tv, &tv, 1); /* XXX what does this do? */
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}
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return (error);
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}
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.Ed
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EFBIG
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An attempt was made to write a file that exceeds the process's file size
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limit or the maximum file size.
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.It Bq Er ENOSPC
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The file system is full.
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.It Bq Er EPERM
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An append-only flag is set on the file, but the caller is attempting to
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write before the current end of file.
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.El
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.Sh SEE ALSO
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.Xr uiomove 9 ,
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.Xr vnode 9
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.Sh AUTHORS
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This man page was written by
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.An Doug Rabson .
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