Date: Sat, 22 Jan 2000 14:08:59 -0500 From: Chuck McCrobie <mccrobi@aplcenMP.apl.jhu.edu> To: fs@FreeBSD.ORG Subject: Re: UDF, userfs Message-ID: <388A004B.12203610@apl.jhu.edu> References: <200001220157.SAA25999@usr09.primenet.com>
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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
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