Re: [dm-devel] block: add a error_count field to struct request

[h...@lst.de]

On Tue, Apr 18, 2017 at 10:57:11PM +, Bart Van Assche wrote:
> Both blk-mq and the traditional block layer support a .cmd_size field to
> make the block layer core allocate driver-specific data at the end of struct
> request. Could that mechanism have been used for the error_count field?

It could, and that's what I did for the modern drivers.  It would have
been a bit of a pain for these old floppy drivers, though.

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Re: [dm-devel] block: add a error_count field to struct request

[Bart Van Assche]

On Tue, 2017-04-18 at 08:52 -0700, Christoph Hellwig wrote:
> From: Christoph Hellwig 
> 
> This is for the legacy floppy and ataflop drivers that currently abuse
> ->errors for this purpose.  It's stashed away in a union to not grow
> the struct size, the other fields are either used by modern drivers
> for different purposes or the I/O scheduler before queing the I/O
> to drivers.
> 
> Signed-off-by: Christoph Hellwig 
> ---
>  include/linux/blkdev.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 5986e1250d7d..e618164462e8 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -175,6 +175,7 @@ struct request {
>   struct rb_node rb_node; /* sort/lookup */
>   struct bio_vec special_vec;
>   void *completion_data;
> + int error_count; /* for legacy drivers, don't use */
>   };
>  
>   /*

Hello Christoph,

Both blk-mq and the traditional block layer support a .cmd_size field to
make the block layer core allocate driver-specific data at the end of struct
request. Could that mechanism have been used for the error_count field?

Thanks,

Bart.

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