On 9/8/22 4:52 AM, Kanchan Joshi wrote:
> 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@xxxxxxxxxxx>
>>> Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
>>> ---
>>> 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.
Agree - if you have to think about operator precedence, then that's a
sign that the code is less readable and more fragile.
--
Jens Axboe
