Re: [Xen-devel] when is the function tdaio_open in block-aio.c called

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-03-15 at 03:33 +0000, hxkhust wrote:
>  Hi,
> 
> I configure my virtual disk like this:
> disk="tap:aio:/path/to/image,hda,w"
> And I add some statements about file operation
> in /xen-4.1.2/tools/blktap/drivers/block-aio.c.
> Then I use "xl create mycfg.hvm" to start the vm.However,my statements
> have not been executed.
> My statements is in the function tdaio_open.During the vmâs
> start,isn't the function tdaio_open
> in /xen-4.1.2/tools/blktap/drivers/block-aio.c called? 

You seem to have patched tools/blktap (AKA blktap1) whereas xl will only
use tools/blktap2.

You don't say which kernel you are running so it is hard to say which
blktap you need.

The xen.git 2.6.32 tree only has blktap2 in it. blktap1 and 2 are both
supported by classic-Xen patchsets (e.g. SuSE forward ports), some
really old kernels support only blktap1. xl will only ever try to use
blktap2 though.

Newer kernels (e.g. mainline 3.0+) do not have any blktap at all, In
this case xl will fallback automatically to using the "qdisk" backend
provided by qemu (be aware that the performance of this is not great)

Ian.



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