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From: Christoph Hellwig <[email protected]>
To: Kanchan Joshi <[email protected]>
Cc: [email protected], [email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], Anuj Gupta <[email protected]>
Subject: Re: [PATCH for-next v7 4/5] block: add helper to map bvec iterator for passthrough
Date: Tue, 20 Sep 2022 14:08:02 +0200	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

> -static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
> +static struct bio *bio_map_get(struct request *rq, unsigned int nr_vecs,
>  		gfp_t gfp_mask)

bio_map_get is a very confusing name.  And I also still think this is
the wrong way to go.  If plain slab allocations don't use proper
per-cpu caches we have a MM problem and need to talk to the slab
maintainers and not use the overkill bio_set here.

> +/* Prepare bio for passthrough IO given an existing bvec iter */
> +int blk_rq_map_user_bvec(struct request *rq, struct iov_iter *iter)

I'm a little confused about the interface we're trying to present from
the block layer to the driver here.

blk_rq_map_user_iov really should be able to detect that it is called
on a bvec iter and just do the right thing rather than needing different
helpers.

> +		/*
> +		 * If the queue doesn't support SG gaps and adding this
> +		 * offset would create a gap, disallow it.
> +		 */
> +		if (bvprvp && bvec_gap_to_prev(lim, bvprvp, bv->bv_offset))
> +			goto out_err;

So now you limit the input that is accepted?  That's not really how
iov_iters are used.   We can either try to reshuffle the bvecs, or
just fall back to the copy data version as blk_rq_map_user_iov does
for 'weird' iters˙

> +
> +		/* check full condition */
> +		if (nsegs >= nr_segs || bytes > UINT_MAX - bv->bv_len)
> +			goto out_err;
> +
> +		if (bytes + bv->bv_len <= nr_iter &&
> +				bv->bv_offset + bv->bv_len <= PAGE_SIZE) {
> +			nsegs++;
> +			bytes += bv->bv_len;
> +		} else
> +			goto out_err;

Nit: This would read much better as:

		if (bytes + bv->bv_len > nr_iter)
			goto out_err;
		if (bv->bv_offset + bv->bv_len > PAGE_SIZE)
			goto out_err;

		bytes += bv->bv_len;
		nsegs++;


  reply	other threads:[~2022-09-20 12:08 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20220909103131epcas5p23d146916eccedf30d498e0ea23e54052@epcas5p2.samsung.com>
2022-09-09 10:21 ` [PATCH for-next v7 0/5] fixed-buffer for uring-cmd/passthru Kanchan Joshi
     [not found]   ` <CGME20220909103136epcas5p38ea3a933e90d9f9d7451848dc3a60829@epcas5p3.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 1/5] io_uring: add io_uring_cmd_import_fixed Kanchan Joshi
     [not found]   ` <CGME20220909103140epcas5p36689726422eb68e6fdc1d39019a4a8ba@epcas5p3.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 2/5] io_uring: introduce fixed buffer support for io_uring_cmd Kanchan Joshi
     [not found]   ` <CGME20220909103143epcas5p2eda60190cd23b79fb8f48596af3e1524@epcas5p2.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 3/5] nvme: refactor nvme_alloc_user_request Kanchan Joshi
2022-09-20 12:02       ` Christoph Hellwig
2022-09-22 15:46         ` Kanchan Joshi
2022-09-23  9:25         ` Kanchan Joshi
     [not found]   ` <CGME20220909103147epcas5p2a83ec151333bcb1d2abb8c7536789bfd@epcas5p2.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 4/5] block: add helper to map bvec iterator for passthrough Kanchan Joshi
2022-09-20 12:08       ` Christoph Hellwig [this message]
2022-09-22 15:23         ` Kanchan Joshi
2022-09-23 15:29           ` Christoph Hellwig
2022-09-23 18:43             ` Kanchan Joshi
2022-09-25 17:46               ` Kanchan Joshi
2022-09-26 14:50               ` Christoph Hellwig
2022-09-27 16:47                 ` Kanchan Joshi
     [not found]   ` <CGME20220909103151epcas5p1e25127c3053ba21e8f8418a701878973@epcas5p1.samsung.com>
2022-09-09 10:21     ` [PATCH for-next v7 5/5] nvme: wire up fixed buffer support for nvme passthrough Kanchan Joshi

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