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Date: Wed, 1 Dec 2010 12:08:15 -0800 (PST)
From: Sage Weil <sage@newdream.net>
To: Greg KH <greg@kroah.com>
cc: Yehuda Sadeh <yehuda@hq.newdream.net>, ceph-devel@vger.kernel.org,
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Subject: Re: [PATCH] rbd: replace the rbd sysfs interface
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On Wed, 1 Dec 2010, Greg KH wrote:
> >  /sys/bus/rbd/{add,remove}
> >  /sys/bus/rbd/devices/<devid>/                 <-- struct device
> >  /sys/bus/rbd/devices/<devid>/{some dev attrs}
> >  /sys/bus/rbd/devices/<devid>/snap_<snapid>/   <-- struct device
> >  /sys/bus/rbd/devices/<devid>/snap_<snapid>/{some snap attrs}
> > 
> > This works, and I is (I hope) using struct device properly.  The only 
> > problem, purely from a user interface standpoint, is that the snaps are 
> > mixed in with attributes, so anybody wanting to iterate over snaps needs 
> > to do something crufty like
> > 
> >  $ for snap in `ls /sys/bus/rbd/devices/$id | grep ^snap_ | cut -c 6-`; do ...
> 
> What's wrong with:
> 	for snap in `ls /sys/bus/rbd/devices/$id/snap_*`; do ...
> instead?

Yeah, it's really the 'cut -c 6-' bit that I was hoping to avoid.  But it 
snaps/ simply doesn't map onto the sysfs paradigm cleanly, that's fine.

That being the case, can we get an Acked-by on the current approach/patch?  
Then I can send something Linus and let him decide what to do for .37.

Thanks!
sage




> 
> And you would be using libudev ideally for a .c file, and iterating over
> the devices is pretty trivial that way from what I have seen.
> 
> > Adding an intermediate snaps/ subdir would let them instead do
> > 
> >  $ for snap in `ls /sys/bus/rbd/devices/$id/snaps/`; do ...
> > 
> > without worrying about the (arbitrarily named) snaps from colliding with 
> > device attributes.  Assuming that is a preferable interface, is the 
> > "right" way to do that to make "snaps" a struct device?  Or is there a 
> > good reason why that is not preferable?
> 
> It's not preferable as that "snaps" directory is a "blank" in the device
> tree, not showing the heiarchy properly.  You can't walk the devices
> back from the devices in snaps/ to the parent properly (i.e. you would
> get stuck at the snaps/ directory as it's not a struct device, but a
> random kobject.
> 
> Hope this helps,
> 
> greg k-h
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