Xen devel - Mar 2012 - when is the function tdaio_open in block-aio.c called

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 vm‘s start,isn't the
function tdaio_open in /xen-4.1.2/tools/blktap/drivers/block-aio.c called?

hxk


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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 vm‘s
> 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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At 2012-03-15 16:56:22,"Ian Campbell" <Ian.Campbell@citrix.com>
wrote:
>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 vm‘s
>> 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.
>
>
I use linux kernel 3.2.9 as dom0's kernel with xen 4.1.2 installed in fedora
14.My purpose is to trace the process in which the raw format vitual disk image
is read.which file is the qdisk backend provided by qemu implemented in?When the
raw image is read,which file or which function is called?

hxk


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On Thu, 2012-03-15 at 09:14 +0000, hxkhust wrote:
> I use linux kernel 3.2.9 as dom0''s kernel with xen 4.1.2 installed
in
> fedora 14.
Then I think you have no blktap (1 or 2) and will therefore be using
qdisk.
> My purpose is to trace the process in which the raw format vitual disk
> image is read.which file is the qdisk backend provided by qemu
> implemented in?When the raw image is read,which file or which function
> is called?
I don''t know. 2s grepping suggests it will be
tools/qemu-xen-traditional-dir/hw/xen_disk.c.

Ian.