[dm-devel] [PATCH 1/2] block: blk_interposer
Damien Le Moal
Damien.LeMoal at wdc.com
Fri Jan 29 01:21:07 UTC 2021
On 2021/01/29 2:23, Sergei Shtepa wrote:
> The block layer interposer allows to intercept bio requests.
> This allows to connect device mapper and other kernel modules
> to the block device stack on the fly.
>
> changes:
> * new BIO_INTERPOSED bio flag.
> * new function __submit_bio_interposed() implements the interposers
> logic.
> * new function blk_mq_is_queue_frozen() allow to assert that
> the queue is frozen.
> * functions blk_interposer_attach() and blk_interposer_detach()
> allow to attach and detach interposers.
The changelog should not be part of the commit message. If you need a changelog
for a single patch, add it between the commit message end "---" and the patch
stats. git will ignore that part.
> Signed-off-by: Sergei Shtepa <sergei.shtepa at veeam.com>
> ---
> block/bio.c | 2 +
> block/blk-core.c | 29 ++++++++++++++
> block/blk-mq.c | 13 +++++++
> block/genhd.c | 82 +++++++++++++++++++++++++++++++++++++++
> include/linux/blk-mq.h | 1 +
> include/linux/blk_types.h | 6 ++-
> include/linux/genhd.h | 19 +++++++++
> 7 files changed, 150 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..07ec82d8fe57 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;
> +
> + bio_set_flag(bio, BIO_INTERPOSED);
> + if (likely(blk_has_interposer(disk)))
> + disk->interposer->ip_submit_bio(bio);
Why do you check again blk_has_interposer() here ? That is checked already in
submit_bio_noacct() and the interposer attach/detach cannot run without the
queue frozen. So I do not think you need to check again. If you do, then you
definitely have a race condition here.
> + else /* interposer was removed */
> + bio_list_add(¤t->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 +1083,9 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
> return BLK_QC_T_NONE;
> }
>
> + if (blk_has_interposer(bio->bi_disk) &&
> + !bio_flagged(bio, BIO_INTERPOSED))
> + return __submit_bio_interposed(bio);
OK. I *think* that this is to handle stacked devices, right ? Otherwise, this
condition does not make much sense. Why not just:
if (blk_has_interposer(bio->bi_disk))
return __submit_bio_interposed(bio);
So at least adding some comments here may be good.
> if (!bio->bi_disk->fops->submit_bio)
> return __submit_bio_noacct_mq(bio);
> return __submit_bio_noacct(bio);
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index f285a9123a8b..924ec26fae5f 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -161,6 +161,19 @@ int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
> }
> EXPORT_SYMBOL_GPL(blk_mq_freeze_queue_wait_timeout);
>
> +
> +bool blk_mq_is_queue_frozen(struct request_queue *q)
> +{
> + bool ret;
> +
> + mutex_lock(&q->mq_freeze_lock);
> + ret = percpu_ref_is_dying(&q->q_usage_counter) && percpu_ref_is_zero(&q->q_usage_counter);
> + mutex_unlock(&q->mq_freeze_lock);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(blk_mq_is_queue_frozen);
Maybe move this change to its own patch preceding this one ?
> +
> /*
> * Guarantee no request is in use, so we can change any data structure of
> * the queue afterward.
> diff --git a/block/genhd.c b/block/genhd.c
> index 419548e92d82..d3459582f56c 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);
>
> /* for extended dynamic devt allocation, currently only one major is used */
> #define NR_EXT_DEVT (1 << MINORBITS)
> @@ -2148,3 +2149,84 @@ static void disk_release_events(struct gendisk *disk)
> WARN_ON_ONCE(disk->ev && disk->ev->block != 1);
> kfree(disk->ev);
> }
> +
> +/**
> + * blk_interposer_attach - Attach interposer to disk
> + * @disk: target disk
> + * @interposer: block device interposer
> + * @ip_submit_bio: hook for submit_bio()
> + *
> + * Returns:
> + * -EINVAL if @interposer is NULL.
> + * -EPERM if queue is not frozen.
> + * -EBUSY if the block device already has @interposer.
> + * -EALREADY if the block device already has @interposer with same callback.
> + *
> + * Disk must be frozen by blk_mq_freeze_queue().
> + */
> +int blk_interposer_attach(struct gendisk *disk, struct blk_interposer *interposer,
> + const ip_submit_bio_t ip_submit_bio)
> +{
> + int ret = 0;
> +
> + if (!interposer)
> + return -EINVAL;
Is this really necessary ? If some user of this function has interposer == NULL,
that caller needs debugging...
> +
> + if (!blk_mq_is_queue_frozen(disk->queue))
> + return -EPERM;
Why not do the queue freeze here ?
> +
> + mutex_lock(&bdev_interposer_mutex);
> + if (blk_has_interposer(disk)) {
> + if (disk->interposer->ip_submit_bio == ip_submit_bio)
> + ret = -EALREADY;
> + else
> + ret = -EBUSY;
> + goto out;
> + }
> +
> + interposer->ip_submit_bio = ip_submit_bio;
> + interposer->disk = disk;
> +
> + disk->interposer = interposer;
> +out:
> + mutex_unlock(&bdev_interposer_mutex);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(blk_interposer_attach);
> +
> +/**
> + * blk_interposer_detach - Detach interposer from disk
> + * @interposer: block device interposer
> + * @ip_submit_bio: hook for submit_bio()
> + *
> + * Disk must be frozen by blk_mq_freeze_queue().
> + */
> +void blk_interposer_detach(struct blk_interposer *interposer,
> + const ip_submit_bio_t ip_submit_bio)
> +{
The interface is weird. Why not passing the gendisk ?
> + struct gendisk *disk;
> +
> + if (WARN_ON(!interposer))
> + return;
Same comment as above. This should not be necessary.
> +
> + mutex_lock(&bdev_interposer_mutex);
> +
> + /* Check if the interposer is still active. */
> + disk = interposer->disk;
> + if (WARN_ON(!disk))
> + goto out;
> +
> + if (WARN_ON(!blk_mq_is_queue_frozen(disk->queue)))
> + goto out;
> +
> + /* Check if it is really our interposer. */
> + if (WARN_ON(disk->interposer->ip_submit_bio != ip_submit_bio))
> + goto out;
> +
> + disk->interposer = NULL;
> + interposer->disk = NULL;
> +out:
> + mutex_unlock(&bdev_interposer_mutex);
> +}
> +EXPORT_SYMBOL_GPL(blk_interposer_detach);
> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index d705b174d346..9d1e8c4e922e 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -525,6 +525,7 @@ void blk_freeze_queue_start(struct request_queue *q);
> void blk_mq_freeze_queue_wait(struct request_queue *q);
> int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
> unsigned long timeout);
> +bool blk_mq_is_queue_frozen(struct request_queue *q);
>
> int blk_mq_map_queues(struct blk_mq_queue_map *qmap);
> void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues);
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 866f74261b3b..6c1351d7b73f 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -227,7 +227,7 @@ struct bio {
> * top bits REQ_OP. Use
> * accessors.
> */
> - unsigned short bi_flags; /* status, etc and bvec pool number */
> + unsigned int bi_flags; /* status, etc and bvec pool number */
> unsigned short bi_ioprio;
> unsigned short bi_write_hint;
> blk_status_t bi_status;
> @@ -304,6 +304,8 @@ enum {
> * of this bio. */
> BIO_CGROUP_ACCT, /* has been accounted to a cgroup */
> BIO_TRACKED, /* set if bio goes through the rq_qos path */
> + BIO_INTERPOSED, /* bio has been interposed and can be moved to
> + * a different disk */
> BIO_FLAG_LAST
> };
>
> @@ -322,7 +324,7 @@ enum {
> * freed.
> */
> #define BVEC_POOL_BITS (3)
> -#define BVEC_POOL_OFFSET (16 - BVEC_POOL_BITS)
> +#define BVEC_POOL_OFFSET (32 - BVEC_POOL_BITS)
> #define BVEC_POOL_IDX(bio) ((bio)->bi_flags >> BVEC_POOL_OFFSET)
> #if (1<< BVEC_POOL_BITS) < (BVEC_POOL_NR+1)
> # error "BVEC_POOL_BITS is too small"
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 809aaa32d53c..8094af3a3db9 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -134,6 +134,14 @@ struct blk_integrity {
> unsigned char tag_size;
> };
>
> +struct blk_interposer;
This is not needed.
> +typedef void (*ip_submit_bio_t) (struct bio *bio);
This hides the definition of the submit callback for no good reasons that I can
see. Since the callback has a simple interface, I would prefer this to be dropped.
> +
> +struct blk_interposer {
> + ip_submit_bio_t ip_submit_bio;
> + struct gendisk *disk;
If you fix the interface of the detach function, you should not need this field.
> +};
> +
> struct gendisk {
> /* major, first_minor and minors are input parameters only,
> * don't use directly. Use disk_devt() and disk_max_parts().
> @@ -158,6 +166,7 @@ struct gendisk {
>
> const struct block_device_operations *fops;
> struct request_queue *queue;
> + struct blk_interposer *interposer;
> void *private_data;
>
> int flags;
> @@ -346,4 +355,14 @@ static inline void printk_all_partitions(void)
> }
> #endif /* CONFIG_BLOCK */
>
> +/*
> + * block layer interposer
> + */
> +#define blk_has_interposer(d) ((d)->interposer != NULL)
Please make this an inline function.
> +
> +int blk_interposer_attach(struct gendisk *disk, struct blk_interposer *interposer,
> + const ip_submit_bio_t ip_submit_bio);
> +void blk_interposer_detach(struct blk_interposer *interposer,
> + const ip_submit_bio_t ip_submit_bio);
> +
> #endif /* _LINUX_GENHD_H */
>
--
Damien Le Moal
Western Digital Research
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