Function vn_write

freebsd/kern/vfs_vnops.c:1047–1127

* File table vnode write routine. */

 * File table vnode write routine.
 */
static int
vn_write(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags,
    struct thread *td)
{
	struct vnode *vp;
	struct mount *mp;
	off_t orig_offset;
	int error, ioflag, lock_flags;
	int advice;

	KASSERT(uio->uio_td == td, ("uio_td %p is not td %p",
	    uio->uio_td, td));
	KASSERT(flags & FOF_OFFSET, ("No FOF_OFFSET"));
	vp = fp->f_vnode;
	if (vp->v_type == VREG)
		bwillwrite();
	ioflag = IO_UNIT;
	if (vp->v_type == VREG && (fp->f_flag & O_APPEND))
		ioflag |= IO_APPEND;
	if (fp->f_flag & FNONBLOCK)
		ioflag |= IO_NDELAY;
	if (fp->f_flag & O_DIRECT)
		ioflag |= IO_DIRECT;
	if ((fp->f_flag & O_FSYNC) ||
	    (vp->v_mount && (vp->v_mount->mnt_flag & MNT_SYNCHRONOUS)))
		ioflag |= IO_SYNC;
	/*
	 * For O_DSYNC we set both IO_SYNC and IO_DATASYNC, so that VOP_WRITE()
	 * implementations that don't understand IO_DATASYNC fall back to full
	 * O_SYNC behavior.
	 */
	if (fp->f_flag & O_DSYNC)
		ioflag |= IO_SYNC | IO_DATASYNC;
	mp = NULL;
	if (vp->v_type != VCHR &&
	    (error = vn_start_write(vp, &mp, V_WAIT | PCATCH)) != 0)
		goto unlock;

	advice = get_advice(fp, uio);

	if (MNT_SHARED_WRITES(mp) ||
	    (mp == NULL && MNT_SHARED_WRITES(vp->v_mount))) {
		lock_flags = LK_SHARED;
	} else {
		lock_flags = LK_EXCLUSIVE;
	}

	vn_lock(vp, lock_flags | LK_RETRY);
	switch (advice) {
	case POSIX_FADV_NORMAL:
	case POSIX_FADV_SEQUENTIAL:
	case POSIX_FADV_NOREUSE:
		ioflag |= sequential_heuristic(uio, fp);
		break;
	case POSIX_FADV_RANDOM:
		/* XXX: Is this correct? */
		break;
	}