On 01/13/2011 03:11 PM, Tejun Heo wrote:

So, as a general rule, when in doubt, just create an attribute.  Let's
refrain from custom symlinkery in sysfs, please.  In this case too, a
holder attribute containing strings like ext[3|4], md, dm or whatnot
would have been _much_ simpler and actually more useful.

Maybe, but this was not invented in DM/MD camp:-)
Probably Kay or Greg can answer why it was done this way?

For DM it just added links to be proper user of it, see
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=f165921df46a977e3561f1bd9f13a348441486d1

Anyway, it is /sys/block - so it represents block devices.

If btrfs internally creates some virtual _block_ device for its pool, it should
present it here too with slaves/holders. If not, why it should create any links there?

Milan