Re: [PATCH v2] block: Use enum for blk-mq tagset flags

[John Garry <john.g.garry@oracle.com>]

On 03/01/2025 06:44, Christoph Hellwig wrote:
> On Thu, Jan 02, 2025 at 02:44:26PM +0000, John Garry wrote:
>> Use an enum for tagset flags, so that they are automatically
>> renumbered when modified and we don't potentially leave
>> unused gaps. Some may find this neater.
> 
> Just as last time around I think this is a bad idea that just creates
> more boilerplate. 

Pros:
- better to not have unused gaps
- catch missing blk-mq debugfs array names
	- this has been a problem in the past

Cons:
- boilerplate

A compromise could be to use some macro to evaluate the flags, like:
#define BLK_MQ_F(flag) (1 << BLK_MQ_B_##flag)

And have, for example:

.flags = BLK_MQ_F(STACKING) | BLK_MQ_F(BLOCKING);

But that will lead to churn in swapping the flag throughout the code and 
maybe also obfuscate, so I highly doubt whether it is even better.

Anyway, I've made my pitch.

> I actually wrote a series before my vacation to
> drop another unused flag, remove the weirdo policy indiretion and
> add better max flag checking while removing code.  Let me rebase
> that, finish writing commit log and send it out.
>