linux-kernel - Re: [PATCH] SCSI: explain the hidden scsi_wait

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Message-ID: <20090618165926.GA13229@uranus.ravnborg.org>
Date:	Thu, 18 Jun 2009 18:59:26 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Stefan Richter <stefanr@...6.in-berlin.de>,
	Matthew Wilcox <matthew@....cx>,
	Changli Gao <xiaosuo@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH] SCSI: explain the hidden scsi_wait_scan Kconfig variable

On Thu, Jun 18, 2009 at 03:21:26PM +0000, James Bottomley wrote:
> On Wed, 2009-06-17 at 12:07 +0200, Stefan Richter wrote:
> > People keep sending patches to expose CONFIG_SCSI_WAIT_SCAN as a tunable
> > item.  These patches aren't accepted upstream, so let's stop the ongoing
> > irritation of people due to this obscure and strange installed module
> > and its Kconfig option.
> > 
> > Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
> > ---
> >  drivers/scsi/Kconfig |   17 ++++++++++++++++-
> >  1 file changed, 16 insertions(+), 1 deletion(-)
> > 
> > Index: b/drivers/scsi/Kconfig
> > ===================================================================
> > --- a/drivers/scsi/Kconfig
> > +++ b/drivers/scsi/Kconfig
> > @@ -259,10 +259,25 @@ config SCSI_SCAN_ASYNC
> >  	  or async on the kernel's command line.
> >  
> >  config SCSI_WAIT_SCAN
> > -	tristate
> > +	tristate  # No prompt here, this is a hidden option.
> 
> Adding comments explaining this is good, I think.
> 
> >  	default m
> >  	depends on SCSI
> >  	depends on MODULES
> > +	help
> > +	  Wait until all the async scans are complete.  The idea is to use
> > +	  it in initrd/ initramfs scripts.  You modprobe it after all the
> > +	  modprobes of the root SCSI drivers and it will wait until they
> > +	  have all finished scanning their buses before allowing the boot
> > +	  to proceed.
> > +
> > +	  Of course this does not work if targets boot independently of and
> > +	  in parallel with the initiator, and/ or with transports with non-
> > +	  deterministic target discovery schemes, and/ or if a transport
> > +	  driver does not support scsi_wait_scan.
> > +
> > +	  Still, this option is not exposed as a prompt because little is
> > +	  to be gained by disabling it, whereas people who accidentally
> > +	  switch it off may wonder why their mkinitrd gets into trouble.
> 
> But not a help text that can never be shown.  Turn this into a comment
> and I'll apply the patch.
> 
> The reason is the fact that this could be construed as a detectable bug
> (option with help that can never be displayed) and someone with too much
> time on their hands someday might make a static checker for it.

In another thread we discussed that the help text should be visible when
searching for an invisible symbol.
There are arguments both ways.

Personally I like the help syntax that we one day can benefit from
and would not accept a warning for help text on symbols with no prompt.

	Sam
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