Re: ConfigFS + Target Mode Engine API discussion

[Nicholas A. Bellinger]

On Fri, 2008-09-12 at 09:24 -0700, Nicholas A. Bellinger wrote:
> On Thu, 2008-09-11 at 01:58 -0700, Nicholas A. Bellinger wrote:
> > On Wed, 2008-09-10 at 23:38 -0700, Joel Becker wrote:
> > > On Wed, Sep 10, 2008 at 09:29:18PM -0700, Nicholas A. Bellinger wrote:
> > > > On Wed, 2008-09-10 at 19:13 -0700, Joel Becker wrote:
> > > > > On Wed, Sep 10, 2008 at 06:42:46PM -0700, Nicholas A. Bellinger wrote:
> > > > > > So I am thinking about the following question:  What would be the
> > > > > > preferred method for calling ct_group_ops->make_group() in order to
> > > > > > create the $CONFIGFS/target/$FABRIC struct config_item directly from
> > > > > > target_fabric_configfs_register() call?  From there, the config group
> > > > > > hanging off $CONFIGFS/target/$FABRIC will be fabric dependent and
> > > > > > providing their own groups, items, depends, from the passed *fabric_cit.
> > > > > > How do I "simulate" a mkdir(2) configfs -> make_group() call coming from
> > > > > > the fabric module itself..?   This would be assuming that both mkdir(2)
> > > > > 
> > > > > 	That's precisely what you don't do with configfs.  It's a
> > > > > defined "not to be done" thing.  So there's no preferred way, there's no
> > > > > way at all.
> > > > > 	What you want do to is drive this from mkdir().  The
> > > > > make_group() will look up the sub-module it needs and return the
> > > > > appropriate item.
> > > > > 
> > > > 
> > > > Whew, good thing I asked about this case first..  :-)
> > > 
> > > 	Can you give me a more complete description of what you're
> > > trying to do?  that way I can maybe help with some suggestions.
> > > 
> > 
> > Sure, the process to get the things up and running would look like:
> > 
> > # Load in the generic target's configfs infrastructure
> > modprobe target_core_configfs
> > 
> > *) $CONFIGFS/target is created with configfs_register_subsystem()
> > 
> > *) $CONFIGFS/target/core is created as a default group under struct
> > configfs_subsystem->su_group to interact with generic target mode
> > engine's storage objects (eg: SCSI HCTL referenced devices, LVM UUID, MD
> > UUID). 
> > 
> > ...........
> > 
> >  # Load LIO-Target using function symbols from target_core_configfs
> > modprobe iscsi_target_mod
> > 
> > module_init() from iscsi_target_mod (eg: the fabric module) calls
> > target_fabric_configfs_register() in target_core_configfs.ko, which is a
> > small wrapper for calling sys_mkdir($CONFIGFS/target/$FABRIC) to kick
> > off the struct config_group_operations->make_group() to create a struct
> > config_item for /sys/kernel/config/target/iscsi (or whatever the fabric
> > is called).
> > 
> > config_item_get() is also called in target_fabric_configfs_register()
> > and returns the newly allocated struct config_item to
> > iscsi_target_mod.ko code to then create new struct config_groups for
> > iSCSI target fabric specific abstractions and LUN mappings between
> > $CONFIGFS/target/core/$STORAGE_OBJECT and Fabric dependent code. I think
> > the latter would be done with symlinks between $FABRIC <-> Generic
> > Target Core Storage Object.
> > 
> > Anyways, knowing that make_group() and drop_item() will *NEVER* be
> > called internally clears up alot for me.  I will keep working on this
> > setup and let you know if I run into any more head scratchers.
> > 
> > Thanks again Joel!
> > 
> 
> Hi Joel,
> 
> After some more thought and a few hours of effort, I was able to get
> some code up using the model above between a new target_core_configfs.ko
> and iscsi_target_mod.ko (LIO-Target):
> 
> http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=commit;h=1a48fb089e1ee1cff5ef02b401d365fdf206cf69
> 
> The one symbol that I required out of fs/namei.c for vfs_mkdir() that

This should have been vfs_rmdir()..  The commit requires no unexported
functions for vfs_mkdir().

--nab

> was not available was lookup_hash(), and the symbol is exported in the
> commit so that
> drivers/lio-core/transport_core_configfs.c:do_configfs_rmdir() works as
> expected.  There is another version of do_configfs_rmdir() that uses the
> exported lookup_one_len(), but that one is not working just quite yet.
> Perhaps there is value in lookup_hash() being defined as
> EXPORT_SYMBOL_GPL().
> 
> Now that the basic configfs structure between a generic engine <->
> fabric is in place, the next steps will be to enable the LIO-Target  and
> LIO-Core IOCTLs into make_group() and drop_item() calls.
> 
> Have a look and let me know what you think..  I will ping you when the
> first pieces of LIO-Target functionality are up and running..
> 
> :-)
> 
> --nab
> 
> 
> 
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