Re: fifo and [acm]time

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

   Date: Mon, 26 Dec 2011 07:50:41 +0000
   From: Mouse <mouse%Rodents-Montreal.ORG@localhost>

   You don't say whether the socket case is SOCK_STREAM or SOCK_DGRAM
   sockets.

For neither type is the socket's [acm]time updated on connect,
write/send, or read/recv.

   The only value I can see in the [acm]time of either a FIFO or an
   AF_LOCAL socket "file" is to see when the relevant software last did
   anything with it.  This is less a matter of an application proper using
   the timestamp and more one of a human who's investigating something
   looking for relevant (or possibly-relevant) data.

Diagnostic information is useful, but is it useful to store on disk?

It seems to me that for the investigation you describe, systems such
as ktrace, dtrace, and filemon would be more appropriate than the
[acm]time of the inode.  However, I suppose they monitor processes,
rather than inodes, and I don't think we have a nice way to monitor an
inode and to be informed of who is doing what to it.

   Is one inode update per minute enough to be a significant issue?

It means the disk must continue spinning and, e.g., will continue to
draw power from a laptop battery to do so, even when the system is
functionally idle.