VOP_RDWR(9) BSD Kernel Developer's Manual VOP_RDWR(9)NAME
VOP_READ, VOP_WRITE — read or write a file
SYNOPSIS
#include <sys/param.h>
#include <sys/vnode.h>
#include <sys/uio.h>
int
VOP_READ(struct vnode *vp, struct uio *uio, int ioflag,
struct ucred *cred);
int
VOP_WRITE(struct vnode *vp, struct uio *uio, int ioflag,
struct ucred *cred);
DESCRIPTION
These entry points read or write the contents of a file
The arguments are:
vp the vnode of the file
uio the location of the data to be read or written
ioflag various flags
cnp the credentials of the caller
The ioflag argument is used to give directives and hints to the filesys‐
tem. When attempting a read, the high 16 bits are used to provide a
read-ahead hint (in units of filesystem blocks) that the filesystem
should attempt. The low 16 bits are a bit mask which can contain the
following flags:
IO_UNIT do I/O as atomic unit
IO_APPEND append write to end
IO_SYNC do I/O synchronously
IO_NODELOCKED underlying node already locked
IO_NDELAY FNDELAY flag set in file table
IO_VMIO data already in VMIO space
LOCKS
The file should be locked on entry and will still be locked on exit.
RETURN VALUES
Zero is returned on success, otherwise an error code is returned.
PSEUDOCODE
int
vop_read(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
{
struct buf *bp;
off_t bytesinfile;
daddr_t lbn, nextlbn;
long size, xfersize, blkoffset;
int error;
size = block size of filesystem;
for (error = 0, bp = NULL; uio->uio_resid > 0; bp = NULL) {
bytesinfile = size of file - uio->uio_offset;
if (bytesinfile <= 0)
break;
lbn = uio->uio_offset / size;
blkoffset = uio->uio_offset - lbn * size;
xfersize = size - blkoffset;
if (uio->uio_resid < xfersize)
xfersize = uio->uio_resid;
if (bytesinfile < xfersize)
xfersize = bytesinfile;
error = bread(vp, lbn, size, NOCRED, &bp);
if (error) {
brelse(bp);
bp = NULL;
break;
}
/*
* We should only get non-zero b_resid when an I/O error
* has occurred, which should cause us to break above.
* However, if the short read did not cause an error,
* then we want to ensure that we do not uiomove bad
* or uninitialized data.
*/
size -= bp->b_resid;
if (size < xfersize) {
if (size == 0)
break;
xfersize = size;
}
error = uiomove((char *)bp->b_data + blkoffset, (int)xfersize, uio);
if (error)
break;
bqrelse(bp);
}
if (bp != NULL)
bqrelse(bp);
return error;
}
int
vop_write(struct vnode *vp, struct uio *uio, int ioflag, struct ucred *cred)
{
struct buf *bp;
off_t bytesinfile;
daddr_t lbn, nextlbn;
off_t osize;
long size, resid, xfersize, blkoffset;
int flags;
int error;
osize = size of file;
size = block size of filesystem;
resid = uio->uio_resid;
if (ioflag & IO_SYNC)
flags = B_SYNC;
else
flags = 0;
for (error = 0; uio->uio_resid > 0;) {
lbn = uio->uio_offset / size;
blkoffset = uio->uio_offset - lbn * size;
xfersize = size - blkoffset;
if (uio->uio_resid < xfersize)
xfersize = uio->uio_resid;
if (uio->uio_offset + xfersize > size of file)
vnode_pager_setsize(vp, uio->uio_offset + xfersize);
if (size > xfersize)
flags |= B_CLRBUF;
else
flags &= ~B_CLRBUF;
error = find_block_in_file(vp, lbn, blkoffset + xfersize,
cred, &bp, flags);
if (error)
break;
if (uio->uio_offset + xfersize > size of file)
set size of file to uio->uio_offset + xfersize;
error = uiomove((char *)bp->b_data + blkoffset, (int) xfersize, uio);
/* XXX ufs does not check the error here. Why? */
if (ioflag & IO_VMIO)
bp->b_flags |= B_RELBUF; /* ??? */
if (ioflag & IO_SYNC)
bwrite(bp);
else if (xfersize + blkoffset == size)
bawrite(bp);
else
bdwrite(bp);
if (error || xfersize == 0)
break;
}
if (error) {
if (ioflag & IO_UNIT) {
VOP_TRUNCATE(vp, osize, ioflag & IO_SYNC, cred, uio->uio_procp);
uio->uio_offset -= resid - uio->uio_resid;
uio->uio_resid = resid;
}
} else if (resid > uio->uio_resid && (ioflag & IO_SYNC)) {
struct timeval tv;
error = VOP_UPDATE(vp, &tv, &tv, 1); /* XXX what does this do? */
}
return error;
}
ERRORS
[ENOSPC] The filesystem is full.
SEE ALSOuiomove(9), vnode(9)AUTHORS
This man page was written by Doug Rabson.
BSD July 24, 1996 BSD
