linux-kernel - Re: [PATCH] configfs: change depends -> select SYSFS

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Date:	Mon, 17 Jan 2011 10:24:20 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
Cc:	James Bottomley <James.Bottomley@...e.de>,
	Stefan Richter <stefanr@...6.in-berlin.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Joel Becker <jlbec@...lplan.org>,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: [PATCH] configfs: change depends -> select SYSFS

On Sun, 16 Jan 2011 22:05:54 -0800 Nicholas A. Bellinger wrote:

> On Sun, 2011-01-16 at 18:22 -0600, James Bottomley wrote:
> > On Mon, 2011-01-17 at 00:06 +0100, Stefan Richter wrote:
> > > On Jan 16 Nicholas A. Bellinger wrote:
> > > > On Sun, 2011-01-16 at 14:11 +0100, Stefan Richter wrote:
> > > > > On Jan 15 Nicholas A. Bellinger wrote:
> > > > > > This patch changes configfs to select SYSFS to fix the following:
> > > > > > 
> > > > > > warning: (TARGET_CORE && GFS2_FS) selects CONFIGFS_FS which has unmet direct dependencies (SYSFS)
> > > > > 
> > > > > Why don't you fix target-core's Kconfig instead?
> > > > 
> > > > The thought here was that since modern configfs is mounted
> > > > at /sys/kernel/config/, selecting SYSFS by default when building
> > > > CONFIGFS_FS made the most sense for existing configfs consumers.
> > > 
> > > I for one think that layered "select" directives will open too many cans
> > > of worms.
> > 
> > select, since we have it, should be clean ... as in if you select
> > something, you don't have to expose yourself to a huge pile of missing
> > depends that only show up in obscure configurations.
> > 
> > 
> > > Best don't use select at all.
> > 
> > The object of select is not to trip up the user.  If we used a purely
> > depend based configuration, the user would have to know to select, say,
> > the right SCSI transport classes before they get presented with drivers.
> > It's completely correct, since transport classes are internal
> > implementations, to have the user select drivers and Kconfig work out
> > via the select directive what transport classes are needed.
> > 
> > > If you use it, select only options that don't depend on anything else.
> > > 
> > > If you feel that people really want you to provide a select for them which
> > > selects something that in turn depends on other things, then I suggest you
> > > rather let your own option depend on these lower dependencies:
> > > 
> > > config HIGHLEVEL_FEATURE
> > > 	tristate "some driver"
> > > 	depends on SYSFS  # because CONFIGFS depends on it
> > > 	select CONFIGFS
> > 
> > This is what I don't understand.
> > 
> > Actually I think the whole premise of the patch (to get back to the
> > original topic) is wrong.
> > 
> > TARGET_CORE depends on SCSI; SCSI has to have sysfs to survive ... we
> > just don't work without it yet we neither select nor depend on it.
> > SYSFS is only deselectable for embedded anyway, so I think the
> > configuration which generated this whole argument was likely a bogus one
> > and consequently, none of the patches are needed (or if they are,
> > they're the tip of the iceberg).
> > 
> 
> This sounds fine for TARGET_CORE, but would still leave GFS2_FS with an
> unmet direct dependency according to the original warning above.
> Unfortuately I do not recall which exactly linux-next build
> configuration was causing this warning to occur from the original post:
> 
> http://marc.info/?l=linux-next&m=129355383112997&w=2
> 
> Any more thoughts here Randy..?


I've looked at GFS2 a bit now and I think that the warning is bogus:

kconfig complains with:
warning: (TARGET_CORE && GFS2_FS) selects CONFIGFS_FS which has unmet direct dependencies (SYSFS)

but the "select" is conditional:
config GFS2_FS
	tristate "GFS2 file system support"
	depends on (64BIT || LBDAF)
	select DLM if GFS2_FS_LOCKING_DLM
	select CONFIGFS_FS if GFS2_FS_LOCKING_DLM
	select SYSFS if GFS2_FS_LOCKING_DLM

and the same condition selects both SYSFS and CONFIGFS_FS.  Furthermore, the
conditional is not true, so neither of them is being selected/enabled.
Looks like a minor kconfig buglet to me.


---
~Randy
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