Re: [PATCH 1/1] block: add default clause for unsupported T10_PI types

[Jens Axboe <axboe@kernel.dk>]

On 9/21/19 4:54 PM, Martin K. Petersen wrote:
> 
> Jens,
> 
>>> block/t10-pi.c: In function 't10_pi_verify':
>>> block/t10-pi.c:62:3: warning: enumeration value 'T10_PI_TYPE0_PROTECTION'
>>>                        not handled in switch [-Wswitch]
>>>         switch (type) {
>>>         ^~~~~~
>>
>> This commit message is woefully lacking. It doesn't explain
>> anything...?  Why aren't we just flagging this as an error? Seems a
>> lot saner than adding a BUG().
> 
> The fundamental issue is that T10_PI_TYPE0_PROTECTION means "no attached
> protection information". So it's a block layer bug if we ever end up in
> this function and the protection type is 0.
> 
> My main beef with all this is that I don't particularly like introducing
> a nonsensical switch case to quiesce a compiler warning. We never call
> t10_pi_verify() with a type of 0 and there are lots of safeguards
> further up the stack preventing that from ever happening. Adding a Type
> 0 here gives the reader the false impression that it's valid input to
> the function. Which it really isn't.
> 
> Arnd: Any ideas how to handle this?

Why not just add the default catch, that logs, and returns the error?
Would seem like the cleanest way to handle it to me. Since the
compiler knows the type, it'll complain if we have missing cases.

-- 
Jens Axboe