blkback name greater than 16 characters issue

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

Hey,

Way back in the past Jan pointed out this issue
http://lists.xenproject.org/archives/html/xen-devel/2015-05/msg03505.html

which is that the device name is "blkback.<domid>.<name>"

for exmaple: blkback.8.xvda, blkback.11.hda

With the multiqueue block backend we add "-%d" for the queue. 
But sadly this is already way past the limit so it gets stripped.


Possible solution had been identified by Ian:
http://lists.xenproject.org/archives/html/xen-devel/2015-05/msg03516.html

	"
	If you are pressed for space then the "xvd" is probably a bit redundant
	in a string which starts blkbk.

	The guest may not even call the device xvdN (iirc BSD has another
	prefix) any how, so having blkback say so seems of limited use anyway.

	Since this seems to not include a partition number how does this work in
	the split partition scheme? (i.e. one where the guest is given xvda1 and
	xvda2 rather than xvda with a partition table)

[It will be 'blkback.8.xvda1', and 'blkback.11.xvda2']

	Perhaps something derived from one of the schemes in
	http://xenbits.xen.org/docs/unstable/misc/vbd-interface.txt might be a
	better fit?
"

[Inline is my answer]

My desire is to easily correlate the name of the thread with the
guest config. And that means preserving the 'xvda' or 'hda' or whatever
the user had in mind.

I believe the domain id is important as well - so we need that.

Which means we are left with the prefix. Should it be 'blkbk' or
should it be completely eliminated? Meaning we have:

 8.xvda
 11.hda

 and
 9.xvda-1
 9.xvda-2
 32100.xvdfg9-5

Or perhaps use 'blk."

blk.32100.xvdfg9-5
(exactly 17, so '5' is gone).

Perhaps in those occassions drop 'blk.' altogether? But I wouldn't want
a special case, so back to:

 32100.xvdfg9-5

? Thoughts?

Or