From owner-freebsd-current Mon Oct 19 20:59:33 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id UAA01847 for freebsd-current-outgoing; Mon, 19 Oct 1998 20:59:33 -0700 (PDT) (envelope-from owner-freebsd-current@FreeBSD.ORG) Received: from firewall.scitec.com.au (fgate.scitec.com.au [203.17.180.68]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id UAA01834 for ; Mon, 19 Oct 1998 20:59:29 -0700 (PDT) (envelope-from john.saunders@scitec.com.au) Received: by firewall.scitec.com.au; id NAA18254; Tue, 20 Oct 1998 13:59:03 +1000 (EST) Received: from mailhub.scitec.com.au(203.17.180.131) by fgate.scitec.com.au via smap (3.2) id xma018232; Tue, 20 Oct 98 13:58:50 +1000 Received: from saruman (saruman.scitec.com.au [203.17.182.108]) by mailhub.scitec.com.au (8.6.12/8.6.9) with SMTP id NAA05981 for ; Tue, 20 Oct 1998 13:58:41 +1000 From: "John Saunders" To: Subject: RE: packet writing Date: Tue, 20 Oct 1998 13:58:39 +1000 Message-ID: <003101bdfbdd$ebed17d0$6cb611cb@saruman.scitec.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook 8.5, Build 4.71.2173.0 Importance: Normal In-Reply-To: <199810192330.RAA26343@panzer.plutotech.com> X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2106.4 Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > > cdrecord-1.6 documents an "experimental" packet writing interface. Can > > someone clue me in as to what this is and the advantages/drawbacks of it? > > All I've heard about it is my cousin's rant about dragging and dropping > > to the CD in lose9x > > I dunno anything about it. Basically packet writing allows you to stop, then re-start, the burn mid track. However when you do this you end up with a few sectors of junk while the laser is stopping and starting. You can then use this feature however you like. Most Windows software are split into fixed packet length and variable packet length methods. The variable packet length writes data continuously until there is no more to write. The fixed packet method breaks all writes up into packets equal to the size of the CDR drives buffer. With fixed size packets you can never underrun, with variable sized packets you can. With fixed sized packets you end of with "junk" sectors mid file, with variable length packets the "junk" sectors are between the files. However to make use of this you need a filesystem able to deal with WORM like media. Each time a file is written or modified a new copy of the file is written to the end of the media. Then a new copy of the directory structure is written to the end of the disk that links to the new file. If a file is deleted then only the directory structure is re-written. The "standard" filesystem for packet writing is called UDF. The spec for it is available from the usual standards bodies. However it's likely that a filesystem supporting a WORM drive will work just as well. > > I fail to see a good reason for an OS-specific in-kernel CD-R driver, > > when the cdrecord package works on plenty of systems that have SCSI > > generic devices (passthrough). Unless I am missing some advantage of > > having CD burning code in the kernel, this strikes me as a horrible > > duplication of effort. So, what am I missing and why is this a good > > idea? :) > > Well, in many ways it is a duplication of effort. It would be > nice to have > the capability to write CD-RW and DVD disks incrementally through a > filesystem-type interface. To do that, you'd need filesystem support > (probably), but also driver-level support for writing to CDs or DVDs. My > guess is that "packet writing" lets you write incrementally to CDs, and > that your cousin's Win95 box is doing it through a filesystem type > interface. For packet writing you could probably get away with just supporting SCSI3/mmc compatible drives. But unless there is some ability to have a user space filesystems (like GNU Hurd) then it will have to be in the kernel. Cheers. -- . +-------------------------------------------------------+ ,--_|\ | John Saunders mailto:John.Saunders@scitec.com.au | / Oz \ | SCITEC LIMITED Phone +61294289563 Fax +61294289933 | \_,--\_/ | "By the time you make ends meet, they move the ends." | v +-------------------------------------------------------+ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message