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References: <20220401110310.611869-1-joshi.k@samsung.com> <CGME20220401110838epcas5p2c1a2e776923dfe5bf65a3e7946820150@epcas5p2.samsung.com>
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From: Kanchan Joshi <joshiiitr@gmail.com>
Date: Tue, 5 Apr 2022 21:19:43 +0530
Message-ID: <CA+1E3rJXrUnmc08Zy3yO=0mGJv1q0CaJez4eUDnTpaJcSh_1FQ@mail.gmail.com>
Subject: Re: [RFC 5/5] nvme: wire-up support for async-passthru on char-device.
To: Christoph Hellwig <hch@lst.de>
Cc: 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>,
=?UTF-8?Q?Javier_Gonz=C3=A1lez?= <javier@javigon.com>,
Anuj Gupta <anuj20.g@samsung.com>
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On Tue, Apr 5, 2022 at 11:32 AM Christoph Hellwig <hch@lst.de> wrote:
>
> 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?
Would be good to have, I suppose.
Helps keeping it simple when user-space wants to use a single-buffer
(otherwise it must carry psuedo iovec for that too).
> 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.
In that case we will base the newer version on its top.