Device Mapper Query

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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Hi  Satyajeet,

On Fri, Jul 20, 2012 at 7:52 PM, Satyajeet [off-list ref]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

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Hello Satyajeet,

On Fri, Jul 20, 2012 at 7:52 PM, Satyajeet [off-list ref]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

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