Subject: Re: [PATCH] [ConfigFS]: Allow symbolic links from a SysFS struct
	kobject source.
From: "Nicholas A. Bellinger" <nab@linux-iscsi.org>
To: Greg KH <greg@kroah.com>
Cc: Joel Becker <joel.becker@oracle.com>, LKML <linux-kernel@vger.kernel.org>,
       Linux-fsdevel <linux-fsdevel@vger.kernel.org>,
       linux-scsi <linux-scsi@vger.kernel.org>,
       "Linux-iSCSI.org Target Dev" 
	<linux-iscsi-target-dev@googlegroups.com>,
       SCST-Devel <scst-devel@lists.sourceforge.net>,
       Alan Stern <stern@rowland.harvard.edu>, Andrew Morton <akpm@osdl.org>,
       Christoph Hellwig <hch@infradead.org>
In-Reply-To: <20081017201017.GA10613@kroah.com>
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	 <20081017173959.GC2221@kroah.com>
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	 <20081017201017.GA10613@kroah.com>
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Date: Fri, 17 Oct 2008 19:41:56 -0700
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On Fri, 2008-10-17 at 13:10 -0700, Greg KH wrote:
> On Fri, Oct 17, 2008 at 12:19:33PM -0700, Nicholas A. Bellinger wrote:
> > On Fri, 2008-10-17 at 10:39 -0700, Greg KH wrote:
> > > On Fri, Oct 17, 2008 at 01:22:18AM -0700, Nicholas A. Bellinger wrote:
> > > > On Fri, 2008-10-17 at 00:44 -0700, Greg KH wrote:
> > > > > On Thu, Oct 16, 2008 at 11:55:55PM -0700, Nicholas A. Bellinger wrote:
> > > > > > Hi Joel, Greg and Co,
> > > > > > 
> > > > > > Here is the the first working code for allowing configfs to handle
> > > > > > symlinks from sysfs struct kobject based code.  Here is the commit:
> > > > > > passing struct kobject into generic target_core_mod subsystem plugins
> > > > > > for locating struct block_device and struct scsi_device..  
> > > > > 
> > > > > Um, no.
> > > > > 
> > > > > You are trying to create symlinks dynamically across superblocks and
> > > > > mount points?  As one of your #warning states, this isn't possible to do
> > > > > correctly, nor is it even a good idea.
> > > > > 
> > > > > So I'd have to reject this patch, sorry.
> > > > > 
> > > > > What is the problem you are attempting to solve here?
> > > > > 
> > > > 
> > > > So, the generic target_core_mod engine that lives
> > > > under /sys/kernel/config/target/core needs a method to locate struct
> > > > block_device and struct scsi_device for access via bio_submit() and
> > > > scsi_execute_() respectively.
> > > 
> > > Then just pass the "name" of the block device into a configfs file,
> > > nothing more is needed, right?
> > > 
> > 
> > What are the preferred methods for accessing struct block_device and
> > struct scsi_device from "name"..?
> 
> call "find_by_name" for a type (this would be block type) and get the
> return value?  Can't remember the actual function call, but it's obvious
> if you look at device.h.
> 

Got it, thanks..

> > > > Originally, target_core_mod used key echoed through configfs attributes
> > > > like so:
> > > > 
> > > > export TARGET=/sys/kernel/config/target/core/
> > > > 
> > > > # Create $STORAGE_OBJECT of type Linux/BLOCK in generic target_core_mod
> > > > mkdir -p $TARGET/iblock_0/lvm_test0
> > > > # OLD METHOD to reference struct block_device
> > > > echo iblock_major=254,iblock_minor=2 > $TARGET/iblock_0/lvm_test0/control
> > > > echo 1 > $TARGET/iblock_0/lvm_test0/enable
> > > > # NEW METHOD using sysfs ->configfs symlinks to reference struct block_device
> > > > ln -s /sys/block/dm-2 $TARGET/iblock_0/lvm_test0/dm-2
> > > 
> > > No, you can't do a symlink across superblocks and expect it to work like
> > > you are thinking internally.
> > > 
> > 
> > <nod>  As I am coding configfs_follow_symlink() to work with sysfs
> > source symlinks I am starting to see that.. :-)  I am still going to
> > hack on it for a bit and see if I can get it running so that it works..
> 
> Even if you get it "to work", it's not going to be able to be accepted,
> sorry.
> 

<nod> not a problem, it was just something that I wanted to see if it
was even possible.  I will refocus on using the method to locate what
Linux storage objects can be used for target_core_mod that Joel
mentioned and your recommendations.

Thanks,

--nab

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