blktap2 questions

blktap2 questions

[Dan Magenheimer]

1) Are there any blkfront version dependencies for blktap2?
Or should I be able to use any existing blkfront that works
today with blktap1 or file: ?

2) Assuming I build and install new dom0 and tools from
xen-unstable, do I need to do anything else to use blktap2?
(The hg log says "Blktap devices are now created directly
on the linux dom0 command line".)  Or is it entirely
transparent (other than ensuring my vhd's use "tap:aio:")?

3) The (ancient?) README says: "will cooperate fine with the
existing backend driver, so you can experiment with tap disks
without breaking existing VM configs"  I assume this means it
cooperates with "file:" backed vhds, not with blktap1?  In
other words, will I be able to use blktap1 with some domains
and blktap2 with others?

Suggestion: Augment the README with the bullets in
the changeset log, and perhaps expand on them (and/or
provide URLs for additional documentation).

Thanks,
Dan

Re: blktap2 questions

[Dutch Meyer]

> 1) Are there any blkfront version dependencies for blktap2?
> Or should I be able to use any existing blkfront that works
> today with blktap1 or file: ?

I'm pretty sure that (a) nobody has tried this and (b) it should work (at 
least in theory).

> 2) Assuming I build and install new dom0 and tools from
> xen-unstable, do I need to do anything else to use blktap2?
> (The hg log says "Blktap devices are now created directly
> on the linux dom0 command line".)  Or is it entirely
> transparent (other than ensuring my vhd's use "tap:aio:")?

It's transparent, we modified the tools to launch the appropriate process. 
Launching it yourself from the command line is just an option, not a 
requirement.

> 3) The (ancient?) README says: "will cooperate fine with the
> existing backend driver, so you can experiment with tap disks
> without breaking existing VM configs"  I assume this means it
> cooperates with "file:" backed vhds, not with blktap1?  In
> other words, will I be able to use blktap1 with some domains
> and blktap2 with others?

blktap1 is still intact and can be used in conjunction with blktap2; 
however, blktap2 takes over most of the tapdisk drivers (like aio), while 
a few others (qcow) still operate in blktap1.  So nothing should keep you 
from using both at once, except that the selection of blktap1 vs blktap2 
is based on the driver you specify.

> Suggestion: Augment the README with the bullets in
> the changeset log, and perhaps expand on them (and/or
> provide URLs for additional documentation).

A good suggestion- the READMEs is embarrasingly out of date (though that 
was to some extent true previously).  We will update soon.

--Dutch

Re: blktap2 questions

[Stefano Stabellini]

Dutch Meyer wrote:

>> 1) Are there any blkfront version dependencies for blktap2?
>> Or should I be able to use any existing blkfront that works
>> today with blktap1 or file: ?
> 
> I'm pretty sure that (a) nobody has tried this and (b) it should work (at 
> least in theory).


I tried with stubdoms and gpl windows pv drivers and it works.