Re: [PATCH] nvme: change nvme_passthru_cmd64's result field.

[Marta Rybczynska]

----- On 31 Oct, 2019, at 14:39, Christoph Hellwig hch@xxxxxx wrote:

> On Wed, Oct 30, 2019 at 10:03:38PM -0700, Charles Machalow wrote:
>> Changing nvme_passthru_cmd64's result field to be backwards compatible
>> with the nvme_passthru_cmd/nvme_admin_cmd struct in terms of the result
>> field. With this change the first 32 bits of result in either case
>> point to CQE DW0. This allows userspace tools to use the new structure
>> when using the old ADMIN/IO_CMD ioctls or new ADMIN/IO_CMD64 ioctls.
> 
> All that casting is a pretty bad idea.  please just add an explicit
> reserved field before the result, and check that it always is zero
> in the ioctl handler.

That would change the size of a structure in UAPI, won't it? 
I wanted to avoid it when adding the *64 ioctls and that's why
I added separate ones instead of extending the ones that exist.

Marta