[PATCH V2 05/13] block: only account passthrough IO from userspace

[Christoph Hellwig]

On Wed, Jan 26, 2022 at 03:21:04PM +0800, Ming Lei wrote:
> > I think the right way would be to just remove this branch entirely.
> > This means we only account bios with a block_device, which implies
> > they have a gendisk.
> 
> That will not account userspace IO, and people may complain.
> 
> We can just account passthrough request from userspace by the patch
> in my last email.

Let's take a step back:  what I/O do we want to account, and how
do we want to archive that?

Assuming accounting is enabled:

 - current mainline accounts all I/O one queues that have a gendisk
 - your original patch accounts file system I/O and some passthrough I/O
   that has a special flag set

Dropping the conditional to grab a bdev from the queue leaves us with
the following rule:

 - all I/O that has a bio and bdev is accounted.  This requires
   passthrough I/O to explicitly set the bdev in case we haven't
   done so, and it requires them to have a bio at all

I guess you are worried about the latter conditionin that we stop
accounting for no data transfer passthrough commands?