Re: [SPDK] BDEV Registration

[Daniel Verkamp <daniel.verkamp at intel.com>]

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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