Re: [PATCH v4 2/6] block: add blk_interposer

blk_interposer allows to intercept bio requests, remap bio to another devices or add new bios.

Signed-off-by: Sergei Shtepa <redacted>
---
 block/bio.c               |  2 +
 block/blk-core.c          | 33 ++++++++++++++++
 block/genhd.c             | 82 +++++++++++++++++++++++++++++++++++++++
 include/linux/blk_types.h |  6 ++-
 include/linux/genhd.h     | 18 +++++++++
 5 files changed, 139 insertions(+), 2 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 1f2cc1fbe283..f6f135eb84b5 100644
--- a/block/bio.c
+++ b/block/bio.c

@@ -684,6 +684,8 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
 	bio_set_flag(bio, BIO_CLONED);
 	if (bio_flagged(bio_src, BIO_THROTTLED))
 		bio_set_flag(bio, BIO_THROTTLED);
+	if (bio_flagged(bio_src, BIO_INTERPOSED))
+		bio_set_flag(bio, BIO_INTERPOSED);
 	bio->bi_opf = bio_src->bi_opf;
 	bio->bi_ioprio = bio_src->bi_ioprio;
 	bio->bi_write_hint = bio_src->bi_write_hint;

diff --git a/block/blk-core.c b/block/blk-core.c
index 7663a9b94b80..c84bc42ba88b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c

@@ -1032,6 +1032,32 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
 	return ret;
 }
 
+static blk_qc_t __submit_bio_interposed(struct bio *bio)
+{
+	struct bio_list bio_list[2] = { };
+	blk_qc_t ret = BLK_QC_T_NONE;
+
+	current->bio_list = bio_list;
+	if (likely(bio_queue_enter(bio) == 0)) {
+		struct gendisk *disk = bio->bi_disk;
+
+		if (likely(blk_has_interposer(disk))) {
+			bio_set_flag(bio, BIO_INTERPOSED);
+			disk->interposer->ip_submit_bio(bio);
+		} else /* interposer was removed */
+			bio_list_add(&current->bio_list[0], bio);

+
+		blk_queue_exit(disk->queue);
+	}
+	current->bio_list = NULL;
+
+	/* Resubmit remaining bios */
+	while ((bio = bio_list_pop(&bio_list[0])))
+		ret = submit_bio_noacct(bio);
+
+	return ret;
+}
+
 /**
  * submit_bio_noacct - re-submit a bio to the block device layer for I/O
  * @bio:  The bio describing the location in memory and on the device.

@@ -1057,6 +1083,13 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
 		return BLK_QC_T_NONE;
 	}
 
+	/*
+	 * Checking the BIO_INTERPOSED flag is necessary so that the bio
+	 * created by the blk_interposer do not get to it for processing.
+	 */
+	if (blk_has_interposer(bio->bi_disk) &&
+	    !bio_flagged(bio, BIO_INTERPOSED))
+		return __submit_bio_interposed(bio);
 	if (!bio->bi_disk->fops->submit_bio)
 		return __submit_bio_noacct_mq(bio);
 	return __submit_bio_noacct(bio);

diff --git a/block/genhd.c b/block/genhd.c
index 419548e92d82..39785a3ef703 100644
--- a/block/genhd.c
+++ b/block/genhd.c

@@ -30,6 +30,7 @@
 static struct kobject *block_depr;
 
 DECLARE_RWSEM(bdev_lookup_sem);
+DEFINE_MUTEX(bdev_interposer_mutex);