geoff@eagle_snax.UUCP ( R.H. coast near the top) (12/19/88)
In article <8812161645.AA10438@monk.proteon.com> jas@proteon.com ("John A. Shriver") writes: >The lack of a public domain PC NFS has very little to do with the >issues of NFS/RPC/UDP/IP/... It has to do with the fact that the >interface to the MS-DOS redirector is essentially a highly-guarded >trade secret of Microsoft, available only if you sign up as a >MS-Networks OEM. This is not cheap, last I knew you had to pay by the >year. There are people who have sucessfully reverse-engineered this >interface (eg. Locus), but they consider it highly valuable >information, and also sell it for a pretty penny. > Actually, there are two ways to implement a redirector under (on top of?) DOS. [And no, I'm not giving away any valuable secrets: anybody with a copy of IBM's PC Watch or a good debugger could figure this out in a moment.] The first, employed by Locus and (by derivation) PC-NFS emulates the DOS system call interface itself by intercepting int21 and a bunch of additional hooks. A definition of this interface has been published in the DOS Technical Reference and other sources; what makes the task hard (and why people guard their implementations jealously) is the fact that the definition is incomplete (there are a couple of critical undocumented calls) and the semantics are inadequately described (e.g. under what circumstances does DOS zero out the rest of a buffer following an incomplete read?). The second way to build a redirector is to intercept the internal int2f multiplex interface used by DOS itself. This is the interface used by the Microsoft redirector for which they charge the big bucks: it has been successfully reverse-engineered, but since the interface is modified at major DOS releases any implementors will be kept busy just staying up to date. >I have no idea what would happen if someone did the reverse >engineering and then put the results in the public domain. Lawsuits? I don't see why there should be any lawsuit. However, the level of effort is such that a successful implementation would become a very valuable asset, and the lure of profit, etc. etc. In addition to PC-NFS, I know of three ongoing efforts to develop PC DOS NFS clients. One (Beame & Whiteside's BW-NFS) was discussed in this newgroup a few months back. The others are still under wraps. As the architect of PC-NFS, I wish them well, with just a touch of pity: after shipping PC-NFS for two and a half years, we are still encountering subtle nuances within DOS which we need to emulate. I know just how busy - and frustrated - they're all going to be! >Oh yes, it would not be hard to make a PC do NFS file service. stan@lbl-csam.arpa (See-Mong Tan) has done a nice job in developing a server at Lawrence Berkeley Laboratory, and as he mentioned in <1485@helios.ee.lbl.gov> LBL and Sun are discussing its possible distribution. >Unfortunately, a PC, it's BIOS, and DOS offer pretty abysmal file >performance, so it would not be a good file server. (Interrupts off >during disk I/O does not help the NFS side of things.) Absolutely - give me a Sun 4/280 with a couple of Super Eagles any day :-) -- Geoff Arnold, Sun Microsystems Inc. +--------------------------------------+ PC Dist. Sys. Group (home of PC-NFS) |When you're fresh out of lawyers, you | UUCP: {hplabs,decwrl...}!sun!garnold |don't know how good it's going to feel| ARPA: garnold@sun.com +--------------------------------------+