Device Mapper Query

Device Mapper Query

[Satyajeet]

Does the dmsetup <dm-dev> <table-file> command, calls the constructor* *
dm_ctr_fn??

If yes what are the argv passed in the dm_ctr_fn, are they the args you
pass to dmsetup??

Is this constructor a callback from dm layer? when it is invoked and how it
is invoked?

Replies will be appreciated.

Regards,
satyajeet
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Device Mapper Query

[Gaurav Mahajan]

Hi  Satyajeet,

On Fri, Jul 20, 2012 at 7:52 PM, Satyajeet <satya.unplugged@gmail.com>wrote:

> Does the dmsetup <dm-dev> <table-file> command, calls the constructor* *
> dm_ctr_fn??

Yes.

> If yes what are the argv passed in the dm_ctr_fn, are they the args you
> pass to dmsetup??
>
True

> Is this constructor a callback from dm layer? when it is invoked and how
> it is invoked?
>

Dm layer registers a fops when ever a new device mapper target is
registered.
So whenever a new device is created then dm refer the fops and call the
respective functions.

To start learning more you can start looking into linear target's code.

Regards,
Gaurav Mahajan.


> Replies will be appreciated.
>
> Regards,
> satyajeet
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
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>
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Device Mapper Query

[Vineet Agarwal]

Hello Satyajeet,

On Fri, Jul 20, 2012 at 7:52 PM, Satyajeet <satya.unplugged@gmail.com>wrote:

> Does the dmsetup <dm-dev> <table-file> command, calls the constructor* *
> dm_ctr_fn??


>
If yes what are the argv passed in the dm_ctr_fn, are they the args you
> pass to dmsetup??
>
> Is this constructor a callback from dm layer? when it is invoked and how
> it is invoked?
>
>
As i understand, dmsetup create calls DM_DEVICE_CREATE which fire two ioctls
1) DM_DEV_CREATE
2) DM_TABLE_LOAD

This first ioctl basically create the dev mapper device.
dev_create ()
|
 -> dm_create ()

The second ioctl basically first creates an empty dm_table and later
populate it. During the population it calls the target constructor.
table_load ()
| dm_table_create ()
| populate_table ()
 |
->dm_table_add_target ()
|
                        -> ctr ()

For further details i would suggest you refer to dm-ioctl.c, dm.c and
dm-table.c

Hope it helps.

-- 
Regards:
Vineet Agarwal


> Replies will be appreciated.
>
> Regards,
> satyajeet
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
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