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- From: barmar@think.uucp (Barry Margolin)
-
- In article <496@usenix.ORG> cowan@marob.masa.com (John Cowan) writes:
- >The difference between unlinking before opening and opening with O_TRUNC is,
- >of course, that the former course of action can change the file's owner,
- >group, and mode settings, whereas the latter course of action cannot.
-
- Does POSIX have the O_CREAT mode flag?
-
- This is related to my favorite complaint as a user of an unusual NFS
- server. We have Symbolics Lisp Machines that run their NFS server, and the
- Symbolics file system has files with version numbers.
-
- When a client is opening an existing file for output there are two ways it
- can do it. It can call the NFS Create entry, or it can call NFS Lookup
- followed by NFS SetAttr to set the length to 0. These two operations have
- equivalent results with a Unix server (although the second requires more
- network operations), but the Symbolics server treats the Create operation
- as a request to create a new version of the file. I thought of having
- SetAttr create a new version when asked to truncate to zero length, but
- this wouldn't help because the client already has a file handle on the
- previous version, and it wouldn't be correct to change the association
- between a file handle and the actual file (a second client might be using
- that file handle).
-
- The SunOS client uses the Create method, and most of our NFS clients are
- Suns, so it's not a major problem. However, Ultrix 3.1 uses the
- Lookup/SetAttr method. We complained to DEC a year or two ago about this
- but they were unsympathetic. The most surprising thing, to me, about this
- lack of sympathy is that DEC's proprietary OS, VMS, has version numbers, so
- I would imagine that this would be a problem for Ultrix clients using VMS
- servers.
- --
- Barry Margolin, Thinking Machines Corp.
-
- barmar@think.com
- {uunet,harvard}!think!barmar
-
- Volume-Number: Volume 21, Number 94
-
-