[dm-devel] [PATCH] dm-mirror: do not degrade the mirror on discard error

[Mikulas Patocka]

On Mon, 16 Feb 2015, James Bottomley wrote:

> I already said this in the first sentence of the last paragraph of my
> email.  The point isn't what it does today it's what might happen
> tomorrow and the principle of least surprise.  One day, someone might
> propagate the error.  When that happens, they'll be surprised to find
> every discard failure reported as -ENOTSUPP and it will cost someone
> time and effort to investigate and fix.  If you just propagate the error
> today, you save all that work in the future.
> 
> James

The question is if this case is so important that it justifies dm-io 
change.

The SSD may ignore discards and report them as sucesfully completed, so no 
one should depend on the return code anyway. The error code may be used as 
a hint that it is futile to send more discards in the future, but relying 
on the return code is already not correct.

Mikulas