# Re: \[PATCH\] block: add a bi\_error field to struct bio

- From: Jens Axboe \<axboe@kernel.dk\>
- Date: 2015-07-22 19:07:44 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2015/07/4540774
- Thread: https://ratatoskr.run/linux-raid/2015/07/4538817/t.md

```text
On 07/20/2015 07:29 AM, Christoph Hellwig wrote:
> Currently we have two different ways to signal an I/O error on a BIO:
>
>   (1) by clearing the BIO_UPTODATE flag
>   (2) by returning a Linux errno value to the bi_end_io callback
>
> The first one has the drawback of only communicating a single possible
> error (-EIO), and the second one has the drawback of not beeing persistent
> when bios are queued up, and are not passed along from child to parent
> bio in the ever more popular chaining scenario.  Having both mechanisms
> available has the additional drawback of utterly confusing driver authors
> and introducing bugs where various I/O submitters only deal with one of
> them, and the others have to add boilerplate code to deal with both kinds
> of error returns.
>
> So add a new bi_error field to store an errno value directly in struct
> bio and remove the existing mechanisms to clean all this up.

I think this is a good change, the only part I _really_ dislike is that this now bumps a struct bio from 2 cache lines to 3. Have you done any perf testing?

-- 
Jens Axboe
```