Re: [Xen-devel] Most up to date blktap2 kernel driver

[Roger Pau Monné <roger.pau@xxxxxxxxxxxxx>]

2011/8/24 Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>:
> On Wed, 24 Aug 2011, Ian Campbell wrote:
>> The Xen backend framework in upstream qemu might also be interesting in
>> this context?
>
> Give a look at hw/xen_backend.c and hw/xen_disk.c in upstream qemu: they
> provide the basic infrustructure to run xen backends in userspace and
> the blkback userspace code.

This looks interesting, it provides an example of how to interact with
grant tables from user space.

>> Does NetBSD have an equivalent of (at least) /dev/xen/gntdev
>> and /dev/xen/evtchn? I think they are a requirement to make this work.
>
> You'll need a way to receive event channel notifications and a way to map
> grant references in userspace.


NetBSD has a device related to Xen events I think (/dev/xenevt), but
hasn't got any gntdev, I'm not sure if that's necessary, I saw that
hw/xen_block.c uses xc_gnttab functions to interact with grant tables,
and they work on NetBSD event though it has no gntdev (but has the
necessary hypercall HYPERVISOR_grant_table_op, I still have to figure
out how is that called from user space).

Regarding kernels, xen.git seems to be missing the blktap2 driver:

http://git.eu.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=tree;f=drivers/xen;h=60ce8f2fa68504158843caefdbb8c6f149a37edf;hb=xen/stable-2.6.32.x

I only see a blktap folder, and no blktap2. Now I'm reading the code from:

http://xenbits.xen.org/hg/linux-2.6.18-xen.hg/file/0b8a9b22b70a/drivers/xen/blktap2

I have a couple of books regarding Xen, the most helpful one being
"The Definitive Guide to the Xen Hypervisor" by David Chisnall, it has
been very helpful in understanding grant tables, but it doesn't have
any information regarding blktap/blktap2 driver internals, and I
cannot find any information apart from the code itself. Is there any
book that contains helpful information about the blktap
implementation?

Thanks, Roger.

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