issuing flush to all namespaces

[Christoph Hellwig]

On Thu, Jul 14, 2022 at 10:08:41AM +0200, Klaus Jensen wrote:
> Hi,
> 
> Since the (very reasonable) changes that cause the driver to check that
> the nsid of the command corresponds to the nsid of the namespace being
> targeted it is no longer possible to issue a flush to all namespaces:
> 
>    # nvme flush /dev/nvme0n1 -n 0xffffffff
>    flush: Invalid argument
> 
> Now, I think we can all agree that Flush is the odd one out here, but
> can we do anything about it? The char devices also check the nsid, so
> they can't be used either.

Don't do it.  Sending flush to all namespaces wasn't even clearly
defined until I think NVMe 1.4 with the supported bits.  It doesn't
really make much sense and there is no point in supporting it in Linux.