[RFC 5/5] nvme: wire-up support for async-passthru on char-device.

[Kanchan Joshi]

On Sat, Apr 23, 2022 at 07:53:09PM +0200, Christoph Hellwig wrote:
>On Wed, Apr 06, 2022 at 10:50:14AM +0530, Kanchan Joshi wrote:
>> > In that case we will base the newer version on its top.
>> But if it saves some cycles for you, and also the travel from nvme to
>> linux-block tree - I can carry that refactoring as a prep patch in
>> this series. Your call.
>
>FYI, this is what I have so far:
>
>http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/nvme-passthrough-refactor
>
>the idea would be to use these lower level helpers for uring, and
>not really share the higher level function at all.  This does create
>a little extra code, but I think it'll be more modular and better
>maintainable.  Feel free to pull this in if it helps you, otherwise
>I'll try to find some time to do more than just light testing and
>will post it.

Thanks for sharing.
So I had picked your previous version, and this one streamlines meta
handling further. But the problem is bip gets freed before we reach to
this point -

+static int nvme_free_user_metadata(struct bio *bio, void __user *ubuf, int ret)
+{
+       struct bio_integrity_payload *bip = bio_integrity(bio);
+       void *buf = bvec_virt(bip->bip_vec);
+
+       if (!ret && bio_op(bio) == REQ_OP_DRV_IN &&
+           copy_to_user(ubuf, buf, bip->bip_vec->bv_len))

Without bip, we cannot kill current meta/meta_len fields.