> +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 block_device *bdev = bio->bi_bdev;
> +
> + if (likely(bdev_has_interposer(bdev))) {
> + bio_set_flag(bio, BIO_INTERPOSED);
> + bdev->bd_interposer->ip_submit_bio(bio);
> + } else {
> + /* interposer was removed */
> + bio_list_add(¤t->bio_list[0], bio);
> + }
> +
> + blk_queue_exit(bdev->bd_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.
> @@ -1043,6 +1071,14 @@ 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 bdev_interposer do not get to it for processing.
> + */
> + if (bdev_has_interposer(bio->bi_bdev) &&
> + !bio_flagged(bio, BIO_INTERPOSED))
> + return __submit_bio_interposed(bio);
> +
> if (!bio->bi_bdev->bd_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 fcc530164b5a..1ae8516643c8 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -30,6 +30,11 @@
> static struct kobject *block_depr;
>
> DECLARE_RWSEM(bdev_lookup_sem);
> +/*
> + * Prevents different block-layer interposers from attaching or detaching
> + * to the block device at the same time.
> + */
> +DEFINE_MUTEX(bdev_interposer_attach_lock);
This one can and should be marked static.
> +int bdev_interposer_attach(struct block_device *bdev, struct bdev_interposer
> *interposer,
Please avoid the overly long line.
> + int ret = 0;
> +
> + if (WARN_ON(!interposer))
WARN_ON_ONCE?
> + return -EINVAL;
> +
> + if (!blk_mq_is_queue_frozen(bdev->bd_disk->queue))
> + return -EPERM;
This probly should be a WARN_ON_ONCE() as well.
> +
> + mutex_lock(&bdev_interposer_attach_lock);
> + if (bdev_has_interposer(bdev)) {
> + if (bdev->bd_interposer->ip_submit_bio == ip_submit_bio)
> + ret = -EALREADY;
> + else
> + ret = -EBUSY;
> + goto out;
> + }
Do we really need the two different error codes here?
> +
> + interposer->ip_submit_bio = ip_submit_bio;
I'd rather let the caller initialize the field instead of passing the
submit function separately.
> +void bdev_interposer_detach(struct bdev_interposer *interposer,
> + const ip_submit_bio_t ip_submit_bio)
> +{
> + /* Check if it is really our interposer. */
> + if (WARN_ON(bdev->bd_interposer->ip_submit_bio != ip_submit_bio))
> + goto out;
I don't really see any need to pass ip_submit_bio just for this check.
> + struct bdev_interposer * bd_interposer;
The * goes just before the member name.
> +/*
> + * block layer interposers structure and functions
> + */
> +typedef void (*ip_submit_bio_t) (struct bio *bio);
> +
> +struct bdev_interposer {
> + ip_submit_bio_t ip_submit_bio;
> + struct block_device *bdev;
Do we need the ip_ prefix here? Also we probably don't really the
the typedef for the function pointer.
> +#define bdev_has_interposer(bd) ((bd)->bd_interposer != NULL)
And inline function would be nice here.
