From owner-freebsd-hackers Tue Sep 19 20: 5:11 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from Gloria.CAM.ORG (Gloria.CAM.ORG [205.151.116.34]) by hub.freebsd.org (Postfix) with ESMTP id 75F3337B423 for ; Tue, 19 Sep 2000 20:05:09 -0700 (PDT) Received: from localhost (intmktg@localhost) by Gloria.CAM.ORG (8.9.3/8.9.3) with ESMTP id XAA12502 for ; Tue, 19 Sep 2000 23:08:22 -0400 Date: Tue, 19 Sep 2000 23:08:22 -0400 (EDT) From: Marc Tardif To: freebsd-hackers@freebsd.org Subject: writing(2) to raw devices Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG 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 write(2), perform raw io on devices such as /dev/rwd0? Doesn't write(2) confine the process to block io by its very nature? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message