Re: [SPDK] BDEV Registration

[Kumaraparameshwaran Rathnavel <krath at cloudsimple.com>]

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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 configuration 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 lib/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(bdev, spdk_bdev_initialize, spdk_bdev_finish, spdk_bdev_config_text))
> 
> SPDK_SUBSYSTEM_REGISTER  in bdev will be executed before main, and add the bdev subsystem.
> 
> It will finally call spdk_bdev_initialize   ->  spdk_bdev_module_initialize  ->  call  module_init.
> Thanks.
> 
> Best Regards,
> Ziye Yang
> 
> -----Original Message-----
> From: SPDK [mailto:spdk-bounces(a)lists.01.org] On Behalf Of Kumaraparameshwaran 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 handles 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 target implementation using SPDK. I need to use the Virtual Subsystem. I see that there is support for RAM disks and I am using it as reference to my Virtual implementation .
>>> 
>>> There is a function called SPDK_BDEV_MODULE_REGISTER in the file lib/bdev/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 defined.  This macro creates a constructor function that adds your bdev module's function pointer table (defined using a spdk_bdev_module_if) to a global list.
>> 
>> Later, when the bdev subsystem is initialized, each bdev module will have its module_init function called, where it should create its bdevs and register 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 determining 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 pointers in fn_table which perform operations on the individual bdevs, like creating 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 also 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 API is still somewhat in flux and not well documented.
>> 
>> Thanks,
>> -- Daniel
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