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From: Kumaraparameshwaran Rathnavel <krath at cloudsimple.com>
Subject: Re: [SPDK] BDEV Registration
Date: Fri, 21 Oct 2016 11:39:17 +0530
Message-ID: <1DB89603-65B0-4308-8B49-507CFC7A4451@cloudsimple.com>
In-Reply-To: FA6C2217B01E9D48A581BB4866021014376507F7@shsmsx102.ccr.corp.intel.com
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To: spdk@lists.01.org

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Thanks for the update.

I am still not clear who should call the function SPDK_SUBSYSTEM_REGISTER. =
I just wanted to add virtual mode subsystem as the NVMe/F target. In config=
uration the Virtual has two Malloc drives. So even before the main function=
 I should create these devices and add. I find SPDK_SUBSYSTEM_REGISTER in l=
ib/bdev/malloc/blocdev_malloc.c . So who should call this function? Should =
I call it by writing a separate program.

Thanking You,
Param =

> =

> Hi Param,
> =

> In the iscsi_tgt's main:
> =

> spdk_app_init  -> spdk_subsystem_init   ->   subsystem->init()
> =

> (bdev is also a subsystem:   registered with  SPDK_SUBSYSTEM_REGISTER(bde=
v, spdk_bdev_initialize, spdk_bdev_finish, spdk_bdev_config_text))
> =

> SPDK_SUBSYSTEM_REGISTER  in bdev will be executed before main, and add th=
e bdev subsystem.
> =

> It will finally call spdk_bdev_initialize   ->  spdk_bdev_module_initiali=
ze  ->  call  module_init.
> Thanks.
> =

> Best Regards,
> Ziye Yang
> =

> -----Original Message-----
> From: SPDK [mailto:spdk-bounces(a)lists.01.org] On Behalf Of Kumaraparame=
shwaran Rathnavel
> Sent: Friday, October 21, 2016 12:09 PM
> To: Storage Performance Development Kit <spdk(a)lists.01.org>
> Subject: Re: [SPDK] BDEV Registration
> =

> Thanks Daniel.
> =

> When will the bdev subsystem get initialised? Which part of the code hand=
les the bdev subsystem initialisation.
> =

> Thanking You,
> Param
>> On 21-Oct-2016, at 3:29 AM, Daniel Verkamp <daniel.verkamp(a)intel.com> =
wrote:
>> =

>> On 10/20/2016 01:11 PM, Kumaraparameshwaran Rathnavel wrote:
>>> Hi All,
>>> =

>>> I have just started using SPDK. I am in need to implement a NVMe/F targ=
et implementation using SPDK. I need to use the Virtual Subsystem. I see th=
at there is support for RAM disks and I am using it as reference to my Virt=
ual implementation .
>>> =

>>> There is a function called SPDK_BDEV_MODULE_REGISTER in the file lib/bd=
ev/malloc/blockdev_malloc.c.
>>> =

>>> How is this function getting called? Who calls this function
>>> =

>>> Regards
>>> Param
>> =

>> Hi Param,
>> =

>> You can find the interface for writing new bdev modules in the header =

>> lib/bdev/bdev_module.h - this is where SPDK_BDEV_MODULE_REGISTER() is de=
fined.  This macro creates a constructor function that adds your bdev modul=
e's function pointer table (defined using a spdk_bdev_module_if) to a globa=
l list.
>> =

>> Later, when the bdev subsystem is initialized, each bdev module will hav=
e its module_init function called, where it should create its bdevs and reg=
ister them using spdk_bdev_register().  Currently, all of the bdevs in SPDK=
 use our configuration file library to read from a common conf file when de=
termining which bdevs are created and what options to use (e.g. the malloc =
bdev uses the [Malloc] section of the configuration file).
>> =

>> When registering a bdev, you must provide another set of function pointe=
rs in fn_table which perform operations on the individual bdevs, like creat=
ing a new I/O channel and submitting I/O requests on a channel.
>> =

>> To hook up your bdev module in the NVMe over Fabrics target, you will al=
so want to modify mk/spdk.modules.mk to add your new module to the BLOCKDEV=
_MODULES list.  This adds linker options to all of the applications in the =
SPDK tree that use bdev modules.
>> =

>> Please let us know if you have any further questions - the bdev module A=
PI is still somewhat in flux and not well documented.
>> =

>> Thanks,
>> -- Daniel
>> _______________________________________________
>> SPDK mailing list
>> SPDK(a)lists.01.org
>> https://lists.01.org/mailman/listinfo/spdk
> =

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