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Date:   Tue, 5 Apr 2022 08:02:24 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Kanchan Joshi <joshiiitr@gmail.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Kanchan Joshi <joshi.k@samsung.com>,
        Jens Axboe <axboe@kernel.dk>, io-uring@vger.kernel.org,
        linux-nvme@lists.infradead.org,
        Pavel Begunkov <asml.silence@gmail.com>,
        Ming Lei <ming.lei@redhat.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Pankaj Raghav <pankydev8@gmail.com>,
        Javier =?iso-8859-1?Q?Gonz=E1lez?= <javier@javigon.com>,
        Anuj Gupta <anuj20.g@samsung.com>
Subject: Re: [RFC 5/5] nvme: wire-up support for async-passthru on
 char-device.
Message-ID: <20220405060224.GE23698@lst.de>
References: <20220401110310.611869-1-joshi.k@samsung.com> <CGME20220401110838epcas5p2c1a2e776923dfe5bf65a3e7946820150@epcas5p2.samsung.com> <20220401110310.611869-6-joshi.k@samsung.com> <20220404072016.GD444@lst.de> <CA+1E3rJ+iWAhUVzVrRDiFTUmp5sNF7wqw_7oVqru2qLCTBQrqQ@mail.gmail.com>
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On Mon, Apr 04, 2022 at 07:55:05PM +0530, Kanchan Joshi wrote:
> > Something like this (untested) patch should help to separate
> > the much better:
> 
> It does, thanks. But the only thing is - it would be good to support
> vectored-passthru too (i.e. NVME_IOCTL_IO64_CMD_VEC) for this path.
> For the new opcode "NVME_URING_CMD_IO" , either we can change the
> cmd-structure or flag-based handling so that vectored-io is supported.
> Or we introduce NVME_URING_CMD_IO_VEC also for that.
> Which one do you prefer?

I agree vectored I/O support is useful.

Do we even need to support the non-vectored case?

Also I think we'll want admin command passthrough on /dev/nvmeX as
well, but I'm fine solving the other items first.

> > +static int nvme_ioctl_finish_metadata(struct bio *bio, int ret,
> > +               void __user *meta_ubuf)
> > +{
> > +       struct bio_integrity_payload *bip = bio_integrity(bio);
> > +
> > +       if (bip) {
> > +               void *meta = bvec_virt(bip->bip_vec);
> > +
> > +               if (!ret && bio_op(bio) == REQ_OP_DRV_IN &&
> > +                   copy_to_user(meta_ubuf, meta, bip->bip_vec->bv_len))
> > +                       ret = -EFAULT;
> 
> Maybe it is better to move the check "bio_op(bio) != REQ_OP_DRV_IN" outside.
> Because this can be common, and for that we can avoid entering into
> the function call itself (i.e. nvme_ioctl_finish_metadata).

Function calls are pretty cheap, but I'll see what we can do.  I'll try
to come up with a prep series to refactor the passthrough support for
easier adding of the io_uring in the next days.