NetBSD Problem Report #6434

Received: (qmail 788 invoked from network); 13 Nov 1998 11:58:00 -0000
Message-Id: <199811131156.WAA06033@zen.quick.com.au>
Date: Fri, 13 Nov 1998 22:56:50 +1100 (EST)
From: "Simon J. Gerraty" <sjg@quick.com.au>
Reply-To: sjg@netbsd.org
To: gnats-bugs@gnats.netbsd.org
Subject: compress/nocompress bit for tapes
X-Send-Pr-Version: 3.95

>Number:         6434
>Category:       kern
>Synopsis:       compress/nocompress bit for tapes
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    kern-bug-people
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Fri Nov 13 04:05:00 +0000 1998
>Closed-Date:    
>Last-Modified:  Fri May 05 19:32:43 +0000 2000
>Originator:     Simon J. Gerraty
>Release:        1.3.2
>Organization:
Zen Programming...
>Environment:

System: NetBSD zen.quick.com.au 1.3.2 NetBSD 1.3.2 (ZEN-PUC) #2: Sun Oct 18 18:37:34 EST 1998 sjg@zen.quick.com.au:/u3/NetBSD/1.3.2/src/sys/arch/i386/compile/ZEN-PUC i386


>Description:

This is a request for enhancment (at Matthew Jacob's suggestion).

Just as there is a reserved bit in the tape device minor number to
control rewind/norewind, it would be very handy to have a bit that
controls whether compression is enabled or not.

--sjg
>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:

From: Todd Vierling <tv@pobox.com>
To: "Simon J. Gerraty" <sjg@quick.com.au>
Cc: gnats-bugs@gnats.netbsd.org, netbsd-bugs@netbsd.org
Subject: Re: kern/6434: compress/nocompress bit for tapes
Date: Fri, 13 Nov 1998 12:02:20 -0500 (EST)

 On Fri, 13 Nov 1998, Simon J. Gerraty wrote:

 : Just as there is a reserved bit in the tape device minor number to
 : control rewind/norewind, it would be very handy to have a bit that
 : controls whether compression is enabled or not.

 What's wrong with "mt compress 1"/"mt compress 0"?

 The problem, of course, now lies in the fact that mt already has this
 capability, and what would mt's actions mean on a device which has a
 "compression enabled" bit as opposed to a "compression disabled" bit?

 -- 
 -- Todd Vierling (Personal tv@pobox.com; Bus. todd_vierling@xn.xerox.com)


From: "Perry E. Metzger" <perry@piermont.com>
To: Todd Vierling <tv@pobox.com>
Cc: "Simon J. Gerraty" <sjg@quick.com.au>, gnats-bugs@gnats.netbsd.org,
        netbsd-bugs@netbsd.org
Subject: Re: kern/6434: compress/nocompress bit for tapes 
Date: Fri, 13 Nov 1998 13:11:36 -0500

 Todd Vierling writes:
 > On Fri, 13 Nov 1998, Simon J. Gerraty wrote:
 > 
 > : Just as there is a reserved bit in the tape device minor number to
 > : control rewind/norewind, it would be very handy to have a bit that
 > : controls whether compression is enabled or not.
 > 
 > What's wrong with "mt compress 1"/"mt compress 0"?

 Why do we need rewinding devices when we have mt rew?

 Perry

From: Todd Vierling <tv@pobox.com>
To: "Perry E. Metzger" <perry@piermont.com>
Cc: "Simon J. Gerraty" <sjg@quick.com.au>, gnats-bugs@gnats.netbsd.org,
        netbsd-bugs@netbsd.org
Subject: Re: kern/6434: compress/nocompress bit for tapes 
Date: Fri, 13 Nov 1998 20:23:07 -0500 (EST)

 On Fri, 13 Nov 1998, Perry E. Metzger wrote:

 : > : Just as there is a reserved bit in the tape device minor number to
 : > : control rewind/norewind, it would be very handy to have a bit that
 : > : controls whether compression is enabled or not.
 : > 
 : > What's wrong with "mt compress 1"/"mt compress 0"?
 : 
 : Why do we need rewinding devices when we have mt rew?

 Good point, but the semantics are a little bit different.  You can "mt rew"
 a rewinding device with well defined behavior.

 What "mt compress 0/1" does on the compress/nocompress device is a little
 more vague; should it keep state on a device declared with a given
 compression state?

 -- 
 -- Todd Vierling (Personal tv@pobox.com; Bus. todd_vierling@xn.xerox.com)


From: "Perry E. Metzger" <perry@piermont.com>
To: Todd Vierling <tv@pobox.com>
Cc: "Perry E. Metzger" <perry@piermont.com>,
        "Simon J. Gerraty" <sjg@quick.com.au>, gnats-bugs@gnats.netbsd.org,
        netbsd-bugs@netbsd.org
Subject: Re: kern/6434: compress/nocompress bit for tapes 
Date: Fri, 13 Nov 1998 20:50:29 -0500

 Todd Vierling writes:
 > On Fri, 13 Nov 1998, Perry E. Metzger wrote:
 > : > What's wrong with "mt compress 1"/"mt compress 0"?
 > : 
 > : Why do we need rewinding devices when we have mt rew?
 > 
 > Good point, but the semantics are a little bit different.  You can "mt rew"
 > a rewinding device with well defined behavior.
 > 
 > What "mt compress 0/1" does on the compress/nocompress device is a little
 > more vague; should it keep state on a device declared with a given
 > compression state?

 Either way is fine so long as it is documented.

From: "Simon J. Gerraty" <sjg@quick.com.au>
To: Todd Vierling <tv@pobox.com>
Cc: "Simon J. Gerraty" <sjg@quick.com.au>, gnats-bugs@gnats.netbsd.org,
        netbsd-bugs@netbsd.org
Subject: Re: kern/6434: compress/nocompress bit for tapes 
Date: Mon, 16 Nov 1998 10:50:22 +1100

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 > From: Todd Vierling <tv@pobox.com>
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 > To: "Simon J. Gerraty" <sjg@quick.com.au>
 > cc: gnats-bugs@gnats.netbsd.org, netbsd-bugs@netbsd.org
 > Subject: Re: kern/6434: compress/nocompress bit for tapes
 > In-Reply-To: <199811131156.WAA06033@zen.quick.com.au>
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 > 
 > On Fri, 13 Nov 1998, Simon J. Gerraty wrote:
 > 
 > : Just as there is a reserved bit in the tape device minor number to
 > : control rewind/norewind, it would be very handy to have a bit that
 > : controls whether compression is enabled or not.
 > 
 > What's wrong with "mt compress 1"/"mt compress 0"?

 Nothing.  But it requires that everytime I feed a tape to Amanda
 I need to run mt(1).  If /dev/nrst0c0 were a norewind,nocompress device
 I could just configure Amanda to use that, and be sure that hw/
 compression would not be used.

 I agree that having a nocompress bit in the minor number might make 
 "mt compress" less interesting, but that does not mean that a
 nocompress bit is not the right thing.  Compression is the sort of
 thing you turn on/off at the start of a mount session, so a minor bit
 controll is quite applicable. 

 In the interests of least surprise, it might be better to use two
 bits in the minor number.

 00 - nothing implied - use mt(1)
 10 - compress off
 11 - compress on

 Thus /dev/nrst0 would continue to be have as it does.

 --sjg



>Unformatted:

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