writing(2) to raw devices

From The Design and Implementation of the 4.4BSD Operating System, the write(2) system call must go through vn_write(), ffs_write(), ffs_balloc(), cluster(), bio() and finally dev() which performs the actual disk write. Considering all this block-oriented overhead, how can dd(1) which calls

Re: writing(2) to raw devices

That is only if the write is to a file within a partition mounted as an FFS file system. vn_write() contains the VOP_WRITE switch, which will switch to the write implementation based on the vnode type. VOP_WRITE calls through the function hanging off the vnode in the vnode op vector at the