On 6/1/18 12:27 AM, Ladvine D Almeida wrote:

On Thursday 31 May 2018 04:46 PM, Jens Axboe wrote:

quoted

On 5/31/18 1:47 AM, Ladvine D Almeida wrote:

quoted

On Monday 28 May 2018 04:54 PM, Jens Axboe wrote:

quoted

On 5/28/18 7:43 AM, Ladvine D Almeida wrote:

quoted

This patch introduces new variable under bio structure to
facilitate inline encryption. This variable is used to
associate I/O requests to crypto information.

Hard no on this, for two reasons:

1) Any additions to struct bio are scrutinized heavily and
   need strong justification.

Thanks for sharing your feedback on the patch.
I am providing reference to an earlier article related to inline encryption support below:
https://urldefense.proofpoint.com/v2/url?u=https-3A__lwn.net_Articles_717754_&d=DwICaQ&c=DPL6_X_6JkXFx7AXWqB0tg&r=z00zRD9ARrwHpe-XSl1OtUp1uNKGYoXI1G2DhOaDDBI&m=m8U0bg9QiswO2oVJgJKq3MmJpqPPK_tN667XwsjojcM&s=9VPcl80YTKwbf8T-oCxWTRahYzS2xNDHZMexpFbuepY&e=

Took a quick look, and this looks like a classic case of something
that should just be a cloned bio. If you clone, you own the bi_private
field, which is what you need.

Cloning the bio gives ownership of the bi_private variable which i can
use to refer to the crypto context.  But i have the following problem
here:
1. In the dm-crypt subsystem, we clone the bio and assign the
bi_private variable. Afterwards, generic_make_request() is done to
submit I/O request to block device.
2. The bio will be cloned further in the below layers. The reference
in the bi_private variable is now lost as the bio_clone function will
not copy the bi_private variable.

Also, the bi_private variable is already used in the dm-crypt layer
for storing its private data. This prevents me from using the same.

If you clone or allocate a bio, you are the owner of bi_private. If
someone further down the stack clones it again, then they own the NEW
bi_private of the newly returned cloned. Nobody will mess with yours,
that would be a layering violation. That is the way to store data on a
per bio basis, not by adding a new random field to the bio structure.

-- 
Jens Axboe