Path: utzoo!dptcdc!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!uw-june!ka
From: ka@june.cs.washington.edu (Kenneth Almquist)
Newsgroups: comp.unix.wizards
Subject: Re: getcwd() and friends.
Summary: O_NDELAY means don't block *forever*.
Message-ID: <7911@june.cs.washington.edu>
Date: 18 Apr 89 23:51:49 GMT
References: <7882@june.cs.washington.edu> <FLEE.89Apr16010720@shire.cs.psu.edu> <10671@bloom-beacon.MIT.EDU>
Organization: U of Washington, Computer Science, Seattle
Lines: 20

jfc@athena.mit.edu (John F Carr) writes:
] In article <FLEE.89Apr16010720@shire.cs.psu.edu> 
]  flee@shire.cs.psu.edu (Felix Lee) writes:
]
]> 2. The open may block.  Kenneth Almquist suggests O_NDELAY, which is
]> fine.  Another alternative is to say that O_TOKEN doesn't block;
]> blocking is only useful if you open for reading or writing.
]
] Suppose you are using NFS over a slow network?  The directory lookups
] may take time, as will the actual open.  The same problem exists with
] slow local media.  You can't guarantee proper error reporting without
] blocking.

The issue is not blocking temporarily while waiting for disk or network
I/O to take place.  The problem is that the open system call, rather than
succeeding or reporting an error, can simply block forever.  The O_NDELAY
flag prevents this under both System V and BSD.  If you run NFS (which is
not part of either System V or BSD UNIX at this point), then the O_NDELAY
flag won't help you.  My suggestion:  don't use NFS.
					Kenneth Almquist