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List:       linux-kernel
Subject:    Re: DEVFSv50 and /dev/fb? (or /dev/fb/? ???)
From:       "Andrew J. Anderson" <andrew () db ! erau ! edu>
Date:       1998-08-12 0:15:47
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On Wed, 12 Aug 1998, Chris Wedgwood wrote:

> Arguably, we could just drop backwards compatibility, as /etc/fstab 
> and getmntent(3) aren't defined by Unix98, but since most unix like 
> OSs have this in some shape of form I don't know how reasonable that is.

Take a look at a snippet from the AIX equivalent of /etc/fstab 
(/etc/filesystems):

/usr:
	dev	= /dev/hd2
	vfs	= jfs
	log	= /dev/hd8
	mount	= automatic
	check	= false
	type	= bootfs
	vol	= /usr
	free	= false

So there is precedence for a "different" format for filesystem
information.  (Even though I would call AIX more "like-unix" than 
"unix-like". ;-)

> I was about to as how often to devices actually get opened anyhow? I
> would thing even on busy systems you could count the number of times
> you access by device per hour on one hand. On most systems, only a
> limited number of users and applications will use device inodes.

I know of a busy POP server that had to increase their connection rate
above 40/sec, and their daemon syslog's every connection (via /dev/log),
so there's at least one documented case.  And let's not forget sendmail
and ftp (in some setups), as well. 

My other thought is a busy telnet server and pty's.  Once you get up there
in users, it may be quite often, perhaps as much as several times a
minute.  Not to mention utilties such as expect that use pty pairs, etc. 
Next would be modem/terminal servers, /dev/log, and perhaps the iBCS
devices when running SCO and Xenix binaries (/dev/inet/tcp and such). 

So if sorting though the /dev directory becomes unreasonable with many
devices, then it truely could become an issue for some applications.  I
believe that I saw a time of up to 0.5 seconds wall clock posted earlier
for an 'ls' on /dev (just tried it here -- 0.47 for 'ls', 3.94 for 'ls
-l'). Consider a 0.5 second delay for a busy mail hub or pop server or ftp
site per message syslog'ed.  Store and forward, anyone? :)

> One last comment... devfs aside, if your are running off RO media,
> how would you handle PCMCIA/USB/1384? (Or is this a silly question?)

Or things like updating /etc/mnttab, and other /etc files are what I
wondered about.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 Andrew Anderson                       http://amelia.db.erau.edu/~andrew/
               if(!(family_tree=fork())){redneck=TRUE;}


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