Re: [Xen-users] tap:ram anyone?

[tim benke <tbenke@xxxxxxxxxxxx>]

On Fri, Jan 9, 2009 at 5:42 PM, Dylan Martin <dmartin@xxxxxxxxxxxx> wrote:

Has anyone ever tried the 'ram' driver with blktap for block devices?

It's mentioned here:

http://wiki.xensource.com/xenwiki/blktap

  Fast shareable RAM disk between VMs (requires some form of

cluster-based filesystem support e.g. OCFS2 in the guest kernel)

and poking around the source, in tools/blktap there is a README

(almost identical to the above web page) and the drivers themselves.

I've been trying to get it to work on CentOS 5.2 to no avail.  Specifically:

 block-attach domain 'tap:ram:/path/to/file' hdb w

..makes something appear in the output of block-list, but the domU

doesn't react at all.  (nothing in dmesg, /dev/dhb is not found

etc...)  Sadly, this is exactly the same thing that happens if you

specify a bogus tap driver, (EG tap:wibble:/path/to/file).

I've tried tap:aio and tap:sync and they both work.

I haven't tried it personally.

There has been very little development on it.

see:
http://lxr.mstier.de/Xen/source/xen_3.2.1/tools/blktap/drivers/block_ram.c?v=3.2.1
http://xen.markmail.org/search/?q=block_ram.c

Maybe some hints in the code and/or changes since the CentOS Xen version.

Cheers,
Todd

I haven't tested the driver myself, I've only copied the descriptions from the README.

This line might help in block_ram.c:207         

DPRINTF("Reading %llu bytes.......",(long long unsigned)s->size << SECTOR_SHIFT);

see if that line appears in your /var/log/messages

..Tim

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