Path: utzoo!attcan!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.wizards
Subject: Re: Tail
Keywords: Tail, Wait, Length
Message-ID: <1616@auspex.auspex.com>
Date: 12 May 89 08:59:23 GMT
References: <11701@eddie.MIT.EDU> <1605@auspex.auspex.com> <4567@psuvax1.cs.psu.edu>
Reply-To: guy@auspex.auspex.com (Guy Harris)
Organization: Auspex Systems, Santa Clara
Lines: 20


 >>>Is there an IOCTL or FCNTRL parameter which allows one to wait for some
 >>>sort of status event (like size change),
 >
 >>Not on any UNIX system with which I'm familiar with 
 >
 >Doesn't the Andrew File System implement callbacks of some sort?

Yes, but - at least according to the USENIX paper - that's only a
notification sent from the server saying that *it* has modified the file
(presumably, either due to a local modification or a remote "pushback");
it says nothing about *local* size changes.

Furthermore, there's no indication that this information is passed up to
userland, and that's the crux of the matter; there's no way for
user-mode code to block waiting for a file to change.  Without that, the
callbacks don't make any difference; with that, the callbacks can be
used, but they'd just be another source of "file changed" notifications
- good old "write", for example, would be another source, and possibly a
more likely one.