diff mbox series

[for-next,v4,3/4] block: add helper to map bvec iterator for passthrough

Message ID 20220905134833.6387-4-joshi.k@samsung.com (mailing list archive)
State New, archived
Headers show
Series [for-next,v4,1/4] io_uring: introduce io_uring_cmd_import_fixed | expand

Commit Message

Kanchan Joshi Sept. 5, 2022, 1:48 p.m. UTC 
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@samsung.com>
Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
---
 block/blk-map.c        | 94 +++++++++++++++++++++++++++++++++++++-----
 include/linux/blk-mq.h |  1 +
 2 files changed, 85 insertions(+), 10 deletions(-)

Comments

Christoph Hellwig Sept. 6, 2022, 6:25 a.m. UTC | #1 
On Mon, Sep 05, 2022 at 07:18:32PM +0530, Kanchan Joshi wrote:
> +static struct bio *bio_map_get(struct request *rq, unsigned int nr_vecs,
>  		gfp_t gfp_mask)
>  {
> @@ -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;

This context looks weird?  That bio_alloc_bioset should not be there,
as biosets are only used for file system I/O, which this is not.
Kanchan Joshi Sept. 6, 2022, 6:33 a.m. UTC | #2 
On Tue, Sep 06, 2022 at 08:25:22AM +0200, Christoph Hellwig wrote:
>On Mon, Sep 05, 2022 at 07:18:32PM +0530, Kanchan Joshi wrote:
>> +static struct bio *bio_map_get(struct request *rq, unsigned int nr_vecs,
>>  		gfp_t gfp_mask)
>>  {
>> @@ -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;
>
>This context looks weird?  That bio_alloc_bioset should not be there,
>as biosets are only used for file system I/O, which this is not.

if you think it's a deal-breaker, maybe I can add a new bioset in nvme and
pass that as argument to this helper. Would you prefer that over the
current approach.
Kanchan Joshi Sept. 6, 2022, 6:47 a.m. UTC | #3 
On Tue, Sep 06, 2022 at 12:03:29PM +0530, Kanchan Joshi wrote:
>On Tue, Sep 06, 2022 at 08:25:22AM +0200, Christoph Hellwig wrote:
>>On Mon, Sep 05, 2022 at 07:18:32PM +0530, Kanchan Joshi wrote:
>>>+static struct bio *bio_map_get(struct request *rq, unsigned int nr_vecs,
>>> 		gfp_t gfp_mask)
>>> {
>>>@@ -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;
>>
>>This context looks weird?  That bio_alloc_bioset should not be there,
>>as biosets are only used for file system I/O, which this is not.
>
>if you think it's a deal-breaker, maybe I can add a new bioset in nvme and
>pass that as argument to this helper. Would you prefer that over the
>current approach.

seems I responded without looking carefully. The bioset addition is not
part of this series. It got added earlier [1] [2], as part of optimizing
polled-io on file/passthru path.

[1] https://lore.kernel.org/linux-block/20220806152004.382170-3-axboe@kernel.dk/
[2] https://lore.kernel.org/linux-block/f2863702-e54c-cd74-efcf-8cb238be1a7c@kernel.dk/
Christoph Hellwig Sept. 6, 2022, 6:51 a.m. UTC | #4 
On Tue, Sep 06, 2022 at 12:03:29PM +0530, Kanchan Joshi wrote:
>> This context looks weird?  That bio_alloc_bioset should not be there,
>> as biosets are only used for file system I/O, which this is not.
>
> if you think it's a deal-breaker, maybe I can add a new bioset in nvme and
> pass that as argument to this helper. Would you prefer that over the
> current approach.

The whole point is that biosets exist to allow for forward progress
guarantees required for file system I/O.  For passthrough I/O
bio_kmalloc is perfectly fine and much simpler.  Adding yet another
bio_set just makes things even worse.
Jens Axboe Sept. 6, 2022, 1:06 p.m. UTC | #5 
On 9/6/22 12:51 AM, Christoph Hellwig wrote:
> On Tue, Sep 06, 2022 at 12:03:29PM +0530, Kanchan Joshi wrote:
>>> This context looks weird?  That bio_alloc_bioset should not be there,
>>> as biosets are only used for file system I/O, which this is not.
>>
>> if you think it's a deal-breaker, maybe I can add a new bioset in nvme and
>> pass that as argument to this helper. Would you prefer that over the
>> current approach.
> 
> The whole point is that biosets exist to allow for forward progress
> guarantees required for file system I/O.  For passthrough I/O
> bio_kmalloc is perfectly fine and much simpler.  Adding yet another
> bio_set just makes things even worse.

It's a performance concern too, efficiency is much worse by using
kmalloc+kfree for passthrough. You don't get bio caching that way.
diff mbox series

Patch

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;
+
+	iter_count = iov_iter_count(iter);
+	nr_segs = iter->nr_segs;
+
+	if (!iter_count || (iter_count >> 9) > queue_max_hw_sectors(q))
+		return -EINVAL;
+	if (nr_segs > queue_max_segments(q))
+		return -EINVAL;
+
+	/* no iovecs to alloc, as we already have a BVEC iterator */
+	bio = bio_map_get(rq, 0, GFP_KERNEL);
+	if (bio == NULL)
+		return -ENOMEM;
+
+	bio_iov_bvec_set(bio, iter);
+	blk_rq_bio_prep(rq, bio, nr_segs);
+
+	/* loop to perform a bunch of sanity checks */
+	bvec_arr = (struct bio_vec *)iter->bvec;
+	for (i = 0; i < nr_segs; i++) {
+		bv = &bvec_arr[i];
+		/*
+		 * 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)) {
+			ret = -EINVAL;
+			goto out_free;
+		}
+
+		/* check full condition */
+		if (nsegs >= nr_segs || bytes > UINT_MAX - bv->bv_len) {
+			ret = -EINVAL;
+			goto out_free;
+		}
+
+		if (bytes + bv->bv_len <= iter_count &&
+				bv->bv_offset + bv->bv_len <= PAGE_SIZE) {
+			nsegs++;
+			bytes += bv->bv_len;
+		} else {
+			ret = -EINVAL;
+			goto out_free;
+		}
+		bvprvp = bv;
+	}
+	return 0;
+out_free:
+	bio_map_put(bio);
+	return ret;
+}
+EXPORT_SYMBOL(blk_rq_map_user_bvec);
+
 /**
  * blk_rq_unmap_user - unmap a request with user data
  * @bio:	       start of bio list
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index b43c81d91892..83bef362f0f9 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -970,6 +970,7 @@  struct rq_map_data {
 	bool from_user;
 };
 
+int blk_rq_map_user_bvec(struct request *rq, struct iov_iter *iter);
 int blk_rq_map_user(struct request_queue *, struct request *,
 		struct rq_map_data *, void __user *, unsigned long, gfp_t);
 int blk_rq_map_user_iov(struct request_queue *, struct request *,