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From: Daniel Verkamp <daniel.verkamp at intel.com>
Subject: Re: [SPDK] BDEV Registration
Date: Thu, 20 Oct 2016 14:59:49 -0700
Message-ID: <c22353ee-7e25-ff66-d9b9-085528f3aa84@intel.com>
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To: spdk@lists.01.org

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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 Virtua=
l 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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