Re: bin/43587: stupid error message during boot from sysctl if no COMPAT40 in kernel

[Wolfgang Stukenbrock <Wolfgang.Stukenbrock%nagler-company.com@localhost>]

The following reply was made to PR bin/43587; it has been noted by GNATS.

From: Wolfgang Stukenbrock <Wolfgang.Stukenbrock%nagler-company.com@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: gnats-admin%NetBSD.org@localhost, netbsd-bugs%NetBSD.org@localhost,
        Wolfgang.Stukenbrock%nagler-company.com@localhost
Subject: Re: bin/43587: stupid error message during boot from sysctl if no 
COMPAT40 in kernel
Date: Fri, 09 Jul 2010 14:37:38 +0200

 Hi Robert,
 
 your aproach is good too.
 Perhaps it is better to avoid an additional read of the old value in 
 case it mayy trigger some actions in the kernel.
 remark: I'm not confirmed with the possibilities of the sysctl-interface 
 here. Perhaps this aspect is obsolete, because there may be no actions 
 inside of the kernel after a read.
 
 But if some tries to set a value that does not fit into the variable 
 (e.g. string to long) shouldn't be silently ignored!
 If it would be possible to catch exactly the read-only case of the 
 variable if the write fails, that should be the sollution.
 
 
 W. Stukenbrock
 
 Robert Elz wrote:
 
 > The following reply was made to PR bin/43587; it has been noted by GNATS.
 > 
 > From: Robert Elz <kre%munnari.OZ.AU@localhost>
 > To: gnats-bugs%NetBSD.org@localhost
 > Cc: 
 > Subject: Re: bin/43587: stupid error message during boot from sysctl if no 
 > COMPAT40 in kernel
 > Date: Fri, 09 Jul 2010 18:49:41 +0700
 > 
 >      Date:        Fri,  9 Jul 2010 10:20:01 +0000 (UTC)
 >      From:        Wolfgang.Stukenbrock%nagler-company.com@localhost
 >      Message-ID:  <20100709102001.394E863BAB7%www.NetBSD.org@localhost>
 >  
 >  Your #1 looks like a reasonable thing to do to me (sysctl nodes shouldn't
 >  exist unless the thing they control exists as well).
 >  
 >    |         2. keep sysctl from setting a variable to the same value with 
 > "?="
 >    |        it has before.
 >  
 >  In addition, I'd also fix sysctl, but not as you suggest there.
 >  Rather, just stop it issuing an error message when it attempts to
 >  set a variable (using ?=) and finds that the variable exists but
 >  cannot be set (for any reason, read-only being the most obvious).
 >  
 >  That I think is totally in keeping with the intent of the ?= operator,
 >  and allows the problem you observed to be "fixed" without needing to
 >  worry about testing whether the value being assigned is the same as the
 >  value there already (just doing the read to test that might cause side
 >  effects in some weird case) now worrying whether the write might be a 
 > trigger
 >  in addition to setting the value.
 >  
 >  kre
 >  
 >