Re: blkback name greater than 16 characters issue

[Wei Liu <wei.liu2@citrix.com>]

On Mon, Dec 14, 2015 at 11:46:35AM -0500, Konrad Rzeszutek Wilk wrote:
> 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 
> 

? Or enlarge TASK_COMM_LEN? :-)

Jokes aside, 'git grep blkback' in tools directory doesn't show any
reference to "blkback" in code (as I would expect), so there is no risk
in breaking tookstack should you change the name.

I don't really have a preference whatsoever on this.

Wei.