linux-kernel - Re: Device mapper support for more than one target ?

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Message-ID: <37d33d830812221054w78fe49f3l6c2896a27c908656@mail.gmail.com>
Date:	Tue, 23 Dec 2008 00:24:49 +0530
From:	"Sandeep K Sinha" <sandeepksinha@...il.com>
To:	"Sandeep K Sinha" <sandeepksinha@...il.com>,
	linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: Device mapper support for more than one target ?

Hey,

On Tue, Dec 23, 2008 at 12:20 AM, Alasdair G Kergon <agk@...hat.com> wrote:
> On Mon, Dec 22, 2008 at 10:52:08PM +0530, Sandeep K Sinha wrote:
>> After looking at the complete implementation of device mappers, I
>> figured out that we can have more than one target for a mapped device
>> then why do we have a check for the number of target to be equal to
>> one , in dm_blk_ioctl ( ) in drivers/md/dm.c
>>
>> http://lxr.linux.no/linux+v2.6.27.10/drivers/md/dm.c#L337
>
> Because whether or not it makes sense to send any specific ioctl to more
> than one target in parallel depends on what that ioctl does.  When we
> added that code we said that we could add hard-coding for specific
> ioctls if the need arose, but so far it hasn't.
>
No, the philosophy should be that we send the ioctl's to the mapped
device and not to the targets underlying that mapped-device.

And doing so, I should be able to access the complete map that belongs
to that mapped device. If I implement an ioctl of my own and try to
serve it, the problem would be that it would never allow me to serve
it if has more than one target.

> Alasdair
> --
> agk@...hat.com
>



-- 
Regards,
Sandeep.





 	
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