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Re: [Xen-devel] How PV frontend and backend initializes?


  • To: tosher 1 <akm2tosher@xxxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Tue, 8 Oct 2019 10:39:11 +0200
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On Sat, Oct 05, 2019 at 10:35:11AM +0000, tosher 1 wrote:
> I was trying to understand the following things regarding the PV driver.
> 
> 1. Who create frontend and backend instances?

That depends on where the frontend and backends run. For example
Linux blkback is implemented as a module of the Linux kernel. Linux
blkfront is also a Linux kernel module. OTOH there's also a block
backend in QEMU called qdisk, which is obviously implemented in QEMU.

I'm however unsure by what you mean with instance, so you might have
to clarify exactly what you mean in order to get a more concise
reply.

> 2. When are these instances created?

The xenstore entries are created at domain creation by the toolstack
(xl/libxl). The connection between the frontend and the backend
happens when the frontend driver loads and initializes the connection.

> 3. How xenbus directories are created? What is the hierarchy of the 
> directories? 

They are created by the toolstack during domain creation: xl/libxl.
There are documents in the public headers that describe the expected
and optional xenstore nodes for each device, see:

http://xenbits.xen.org/gitweb/?p=xen.git;a=tree;f=xen/include/public/io

> 4. What is the role of "vifname" and who sets it?

That's set in the guest config file [0] and then it's the hotplug
script the one in charge of renaming the interface from it's original
name into the desired one [1].

Roger.

[0] 
https://xenbits.xen.org/docs/unstable/man/xl-network-configuration.5.html#vifname
[1] 
http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/hotplug/Linux/vif-common.sh#l67

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