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 filesystem. 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 ALSO
uiomove(9), vnode(9)

AUTHORS
This man page was written by Doug Rabson.