i'm well aware of Plan 9's decisions in this area.
having had this discussion with Rob and others in what was still 1127 at Murray Hill, my conclusion is that the decision hinged less on the desirability of the semantics than the complexity of sorting out correct behavior in the presence of snapshots or logs in the file server.
not everyone in 1127 was thrilled by the omission.
others have shown one can solve those problems quite nicely so sacrificing the capabilities is unnecessary. eg Network Appliances filesystem services with snapshots, various log-based filesystems for Linux, XFS from SGI, and ZFS from Sun.
what is true is that relaxing those semantics makes it easier to map "unix file semantics" onto more systems - ie, it increases portability. the clever hack pulled by NFS recognizes that the most common use of creat()/unlink()/use is in fact, mk*temp() kind of things and hence it's worth the trouble to make that work.
however, the various complaints about "never put mailboxes on NFS" also arise precisely because the semantics have been blurred to allow assorted significantly different filesystem implementations to be vended by NFS. that means precise locking and sequencing behavior cannot be guaranteed with NFS. it's not the fault of NFS - that's what comes with the increased portability (note i've avoided saying "improved" portability).
According to Rusty Sandberg, I was the first person outside of the authors of VFS first done in SunOS 3.5 to write a filesystem which plugged into the system and supported an alien filesystem format. and they had not written a new one, just put a VFS front-end on the existing UFS code to keep it working.
That was quite a shake-down cruise and more than a few of these issues got discussed at considerable length.
cheers,
-moRalph Corderoy wrote:
Hi mo,
the reference-count semantics are immensely useful, but not without cost. it complicates the design of NFS no small amount and is why hard links cannot cross demountable volumes. however, doing without those semantics is very difficult to imagine.
What you say is true, but it may be of interest that Bell Labs dropped the link count IIRC in Plan 9, Unix's successor.
http://plan9.bell-labs.com/magic/man2html/2/stat
Cheers,
Ralph.
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