Re: [SPDK] BDEV Registration

[Kumaraparameshwaran Rathnavel <krath at cloudsimple.com>]

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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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