[PATCH for-next v5 3/4] block: add helper to map bvec iterator for passthrough

[Kanchan Joshi]

On Wed, Sep 07, 2022 at 03:32:26PM +0000, Chaitanya Kulkarni wrote:
>On 9/5/22 23:27, Kanchan Joshi wrote:
>> Add blk_rq_map_user_bvec which maps the bvec iterator into a bio and
>> places that into the request. This helper will be used in nvme for
>> uring-passthrough with fixed-buffer.
>> While at it, create another helper bio_map_get to reduce the code
>> duplication.
>>
>> Signed-off-by: Kanchan Joshi <joshi.k at samsung.com>
>> Signed-off-by: Anuj Gupta <anuj20.g at samsung.com>
>> ---
>>   block/blk-map.c        | 94 +++++++++++++++++++++++++++++++++++++-----
>>   include/linux/blk-mq.h |  1 +
>>   2 files changed, 85 insertions(+), 10 deletions(-)
>>
>> diff --git a/block/blk-map.c b/block/blk-map.c
>> index f3768876d618..e2f268167342 100644
>> --- a/block/blk-map.c
>> +++ b/block/blk-map.c
>> @@ -241,17 +241,10 @@ static void bio_map_put(struct bio *bio)
>>   	}
>>   }
>>
>> -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)
>>   {
>> -	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
>> -	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
>>   	struct bio *bio;
>> -	int ret;
>> -	int j;
>> -
>> -	if (!iov_iter_count(iter))
>> -		return -EINVAL;
>>
>>   	if (rq->cmd_flags & REQ_POLLED) {
>>   		blk_opf_t opf = rq->cmd_flags | REQ_ALLOC_CACHE;
>> @@ -259,13 +252,31 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
>>   		bio = bio_alloc_bioset(NULL, nr_vecs, opf, gfp_mask,
>>   					&fs_bio_set);
>>   		if (!bio)
>> -			return -ENOMEM;
>> +			return NULL;
>>   	} else {
>>   		bio = bio_kmalloc(nr_vecs, gfp_mask);
>>   		if (!bio)
>> -			return -ENOMEM;
>> +			return NULL;
>>   		bio_init(bio, NULL, bio->bi_inline_vecs, nr_vecs, req_op(rq));
>>   	}
>> +	return bio;
>> +}
>> +
>> +static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
>> +		gfp_t gfp_mask)
>> +{
>> +	unsigned int max_sectors = queue_max_hw_sectors(rq->q);
>> +	unsigned int nr_vecs = iov_iter_npages(iter, BIO_MAX_VECS);
>> +	struct bio *bio;
>> +	int ret;
>> +	int j;
>> +
>> +	if (!iov_iter_count(iter))
>> +		return -EINVAL;
>> +
>> +	bio = bio_map_get(rq, nr_vecs, gfp_mask);
>> +	if (bio == NULL)
>> +		return -ENOMEM;
>>
>>   	while (iov_iter_count(iter)) {
>>   		struct page **pages, *stack_pages[UIO_FASTIOV];
>> @@ -612,6 +623,69 @@ int blk_rq_map_user(struct request_queue *q, struct request *rq,
>>   }
>>   EXPORT_SYMBOL(blk_rq_map_user);
>>
>> +/* Prepare bio for passthrough IO given an existing bvec iter */
>> +int blk_rq_map_user_bvec(struct request *rq, struct iov_iter *iter)
>> +{
>> +	struct request_queue *q = rq->q;
>> +	size_t iter_count, nr_segs;
>> +	struct bio *bio;
>> +	struct bio_vec *bv, *bvec_arr, *bvprvp = NULL;
>> +	struct queue_limits *lim = &q->limits;
>> +	unsigned int nsegs = 0, bytes = 0;
>> +	int ret, i;
>> +
>
>consider this (untested), it also sets the variable i data type same
>as it comparison variable in nr_segs the loop i.e. size_t :-
>
>+       struct bio_vec *bv, *bvec_arr, *bvprvp = NULL;
>+       struct request_queue *q = rq->q;
>+       struct queue_limits *lim = &q->limits;
>+       unsigned int nsegs = 0, bytes = 0;
>+       size_t iter_count, nr_segs, i;
>+       struct bio *bio;
>+       int ret;
>
>
>> +	iter_count = iov_iter_count(iter);
>> +	nr_segs = iter->nr_segs;
>> +
>> +	if (!iter_count || (iter_count >> 9) > queue_max_hw_sectors(q))
>> +		return -EINVAL;
>
>can we remove braces for iter_count >> 9 without impacting the intended
>functionality?

I think removing that make it hard to read.
I will fold all other changes you mentioned in v6.