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[dm-devel] Re: Device mapper support for more than one target ?


On Tue, Dec 23, 2008 at 12:20 AM, Alasdair G Kergon <agk redhat 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 redhat com


"To learn is to change. Education is a process that changes the learner."

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