From owner-freebsd-fs Sat Jan 22 11: 4:57 2000 Delivered-To: freebsd-fs@freebsd.org Received: from aplcenMP.apl.jhu.edu (apl.jhu.edu [128.220.101.100]) by hub.freebsd.org (Postfix) with ESMTP id D206A14EB5 for ; Sat, 22 Jan 2000 11:04:53 -0800 (PST) (envelope-from mccrobi@aplcenMP.apl.jhu.edu) Received: from apl.jhu.edu (kslip13.apl.jhu.edu [128.220.108.23]) by aplcenMP.apl.jhu.edu (8.9.3/8.9.1) with ESMTP id OAA14223 for ; Sat, 22 Jan 2000 14:05:55 -0500 (EST) Message-ID: <388A004B.12203610@apl.jhu.edu> Date: Sat, 22 Jan 2000 14:08:59 -0500 From: Chuck McCrobie X-Mailer: Mozilla 4.51 [en] (X11; I; FreeBSD 3.3-RELEASE i386) X-Accept-Language: en MIME-Version: 1.0 To: fs@FreeBSD.ORG Subject: Re: UDF, userfs References: <200001220157.SAA25999@usr09.primenet.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org There are some file systems in the commerical world that "uplink" to a user mode daemon that does the actual on-disk work. Without naming names, I can think of at least two that actually do this... They present a pseudo-device which the end-user mounts. This pseudo-device catches all the file system requests and "up calls" the user mode daemon. The user mode daemon than talks to the real device to perform the i/o. I may be able to provide details of the process from another Unix system, but not actual code. This approach seems to handle many o/s'es in that the daemon can be made somewhat portable. The pseudo-device, however, is of necessity o/s specific. One may send flames this way, but I'm also wondering about doing this for NT also. A pseudo-device to catch the file system IRP's, up call some "NT Service" which actually does the on-disk managment and I/O to the real device. Please note that I'm not interested in placing more than one slice on a disk. My background is optical where, typically, one file system slice is laid down on the entire surface. I'm wondering about the actual performance of such a file system. The user mode daemon would have to compete for disk/page with other user mode programs. Perhaps this is not too bad. Chuck McCrobie (** MAD VAX **) To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message