Проект OpenNet: MAN VOP_READ (9) Ядро (FreeBSD и Linux)

Интерактивная система просмотра системных руководств (man-ов)

VOP_READ (9)

>> VOP_READ (9) ( FreeBSD man: Ядро )

BSD mandoc

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:

Fa vp: The vnode of the file.
Fa uio: The location of the data to be read or written.
Fa ioflag: Various flags.
Fa cnp: The credentials of the caller.

The Fa ioflag argument is used to give directives and hints to the file system. When attempting a read, the high 16 bits are used to provide a read-ahead hint (in units of file system blocks) that the file system 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 file system;

    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 file system;
    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) {
            /* call private routine to truncate file. */
            your_truncate(vp, osize, ioflag & IO_SYNC, cred, uio->uio_td);
            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

Bq Er EFBIG: An attempt was made to write a file that exceeds the process's file size limit or the maximum file size.
Bq Er ENOSPC: The file system is full.
Bq Er EPERM: An append-only flag is set on the file, but the caller is attempting to write before the current end of file.