0734b428c7
possible when writing:
[EFBIG] An attempt was made to write a file that exceeds
the process's file size limit or the maximum file
size.
[EPERM] An append-only flag is set on the file, but the
caller is attempting to write before the current
end of file.
238 lines
6.1 KiB
Groff
238 lines
6.1 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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.Fd #include <sys/param.h>
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.Fd #include <sys/vnode.h>
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.Fd #include <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 Ar vp
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the vnode of the file
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.It Ar uio
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the location of the data to be read or written
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.It Ar ioflag
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various flags
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.It Ar 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 filesystem.
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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 filesystem blocks) that the filesystem
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should attempt. 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 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 filesystem;
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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 filesystem;
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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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VOP_TRUNCATE(vp, osize, ioflag & IO_SYNC, cred, uio->uio_procp);
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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 filesystem 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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