Re: [Xen-devel] [PATCH 0 of 9 RFC v2] blktap3: Introduce a small subset of blktap3 files

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2012-12-04 at 18:19 +0000, Thanos Makatos wrote:
> 2. tapdisk: a user space process that receives block I/O requests from
>    blkfront, translates them to whatever the current backing file format is
>    (i.e. RAW, VHD, qcow etc.), and performs the actual I/O. Apart from block
>    I/O requests, the tapdisk also allows basic management of each virtual
>    block device, e.g. a device may be temporarily paused. tapdisk listens to
>    a loopback socket for such commands. The tap-ctl utility (explained later)
>    can be used for managing the tapdisk.
[...]
> 4. tapback: a user space daemon that acts as the back-end of each virtual
>    block device: it monitors XenStore for the block front-end's state changes,
>    creates/destroys the shared ring, and instructs the tapdisk to connect
>    to/disconnect from the shared ring. It also communicates to the block
>    front-end required parameters (e.g. block device size in sectors) via
>    XenStore.

There is 1 tapdisk per VBD but how many tapbacks are there? One per VBD
as well or one per domain or per driver domain?

Is tapback involved in things after the ring has been setup and it has
instructed tapdisk to use it? i.e. is it on the datapath at all?

Ian.


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