Message-ID: <BL0PR04MB65141320C7BF75B7142CA30CE71C0@BL0PR04MB6514.namprd04.prod.outlook.com>
Date:   Wed, 21 Oct 2020 09:21:36 +0000
From:   Damien Le Moal <Damien.LeMoal@....com>
To:     Sergei Shtepa <sergei.shtepa@...am.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "hch@...radead.org" <hch@...radead.org>,
        "darrick.wong@...cle.com" <darrick.wong@...cle.com>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "len.brown@...el.com" <len.brown@...el.com>,
        "pavel@....cz" <pavel@....cz>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        Johannes Thumshirn <Johannes.Thumshirn@....com>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>,
        "jack@...e.cz" <jack@...e.cz>, "tj@...nel.org" <tj@...nel.org>,
        "gustavo@...eddedor.com" <gustavo@...eddedor.com>,
        "bvanassche@....org" <bvanassche@....org>,
        "osandov@...com" <osandov@...com>,
        "koct9i@...il.com" <koct9i@...il.com>,
        "steve@....org" <steve@....org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/2] Block layer filter - second version

On 2020/10/21 18:04, Sergei Shtepa wrote:
> Signed-off-by: Sergei Shtepa <sergei.shtepa@...am.com>
> ---
>  block/Kconfig               |  11 ++
>  block/Makefile              |   1 +
>  block/blk-core.c            |  52 +++++--
>  block/blk-filter-internal.h |  29 ++++
>  block/blk-filter.c          | 286 ++++++++++++++++++++++++++++++++++++
>  block/partitions/core.c     |  14 +-
>  fs/block_dev.c              |   6 +-
>  fs/direct-io.c              |   2 +-
>  fs/iomap/direct-io.c        |   2 +-
>  include/linux/bio.h         |   4 +-
>  include/linux/blk-filter.h  |  76 ++++++++++
>  include/linux/genhd.h       |   8 +-
>  kernel/power/swap.c         |   2 +-
>  mm/page_io.c                |   4 +-
>  14 files changed, 471 insertions(+), 26 deletions(-)
>  create mode 100644 block/blk-filter-internal.h
>  create mode 100644 block/blk-filter.c
>  create mode 100644 include/linux/blk-filter.h
> 
> diff --git a/block/Kconfig b/block/Kconfig
> index bbad5e8bbffe..a308801b4376 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -204,6 +204,17 @@ config BLK_INLINE_ENCRYPTION_FALLBACK
>  	  by falling back to the kernel crypto API when inline
>  	  encryption hardware is not present.
>  
> +config BLK_FILTER
> +	bool "Enable support for block layer filters"
> +	default y
> +	depends on MODULES
> +	help
> +	  Enabling this lets third-party kernel modules intercept
> +	  bio requests for any block device. This allows them to implement
> +	  changed block tracking and snapshots without any reconfiguration of
> +	  the existing setup. For example, this option allows snapshotting of
> +	  a block device without adding it to LVM.
> +
>  menu "Partition Types"
>  
>  source "block/partitions/Kconfig"
> diff --git a/block/Makefile b/block/Makefile
> index 8d841f5f986f..b8ee50b8e031 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -38,3 +38,4 @@ obj-$(CONFIG_BLK_SED_OPAL)	+= sed-opal.o
>  obj-$(CONFIG_BLK_PM)		+= blk-pm.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION)	+= keyslot-manager.o blk-crypto.o
>  obj-$(CONFIG_BLK_INLINE_ENCRYPTION_FALLBACK)	+= blk-crypto-fallback.o
> +obj-$(CONFIG_BLK_FILTER)	+= blk-filter.o
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 10c08ac50697..cc06402af695 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1216,23 +1216,20 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
>  EXPORT_SYMBOL(submit_bio_noacct);

Probably best to have this as its own patch last in the series.

>  
>  /**
> - * submit_bio - submit a bio to the block device layer for I/O
> - * @bio: The &struct bio which describes the I/O
> - *
> - * submit_bio() is used to submit I/O requests to block devices.  It is passed a
> - * fully set up &struct bio that describes the I/O that needs to be done.  The
> - * bio will be send to the device described by the bi_disk and bi_partno fields.
> + * submit_bio_direct - submit a bio to the block device layer for I/O
> + * bypass filter.
> + * @bio:  The bio describing the location in memory and on the device.
>   *
> - * The success/failure status of the request, along with notification of
> - * completion, is delivered asynchronously through the ->bi_end_io() callback
> - * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
> - * been called.
> + * Description:
> + *    This is a version of submit_bio() that shall only be used for I/O
> + *    that cannot be intercepted by block layer filters.
> + *    All file systems and other upper level users of the block layer
> + *    should use submit_bio() instead.
> + *    Use this function to access the swap partition and directly access
> + *    the block device file.
>   */
> -blk_qc_t submit_bio(struct bio *bio)
> +blk_qc_t submit_bio_direct(struct bio *bio)
>  {
> -	if (blkcg_punt_bio_submit(bio))
> -		return BLK_QC_T_NONE;
> -
>  	/*
>  	 * If it's a regular read/write or a barrier with data attached,
>  	 * go through the normal accounting stuff before submission.
> @@ -1282,8 +1279,35 @@ blk_qc_t submit_bio(struct bio *bio)
>  
>  	return submit_bio_noacct(bio);
>  }
> +EXPORT_SYMBOL(submit_bio_direct);

EXPORT_SYMBOL_GPL

> +
> +/**
> + * submit_bio - submit a bio to the block device layer for I/O
> + * @bio: The &struct bio which describes the I/O
> + *
> + * submit_bio() is used to submit I/O requests to block devices.  It is passed a
> + * fully set up &struct bio that describes the I/O that needs to be done.  The
> + * bio will be send to the device described by the bi_disk and bi_partno fields.
> + *
> + * The success/failure status of the request, along with notification of
> + * completion, is delivered asynchronously through the ->bi_end_io() callback
> + * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
> + * been called.
> + */
> +void submit_bio(struct bio *bio)
> +{
> +	if (blkcg_punt_bio_submit(bio))
> +		return;
> +
> +#ifdef CONFIG_BLK_FILTER> +	blk_filter_submit_bio(bio);
> +#else
> +	submit_bio_direct(bio);
> +#endif


	if (IS_ENABLED(CONFIG_BLK_FILTER))
		blk_filter_submit_bio(bio);
	else
		submit_bio_direct(bio);

is much cleaner...


> +}
>  EXPORT_SYMBOL(submit_bio);
>  
> +
>  /**
>   * blk_cloned_rq_check_limits - Helper function to check a cloned request
>   *                              for the new queue limits


The remaining should probably be a different patch before the above change.

> diff --git a/block/blk-filter-internal.h b/block/blk-filter-internal.h
> new file mode 100644
> index 000000000000..d456a09f50db
> --- /dev/null
> +++ b/block/blk-filter-internal.h
> @@ -0,0 +1,29 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + *
> + * Block device filters internal declarations
> + */
> +
> +#ifndef BLK_FILTER_INTERNAL_H
> +#define BLK_FILTER_INTERNAL_H
> +
> +#ifdef CONFIG_BLK_FILTER
> +#include <linux/blk-filter.h>
> +
> +void blk_filter_part_add(struct hd_struct *part, dev_t devt);
> +
> +void blk_filter_part_del(struct hd_struct *part);
> +
> +#else /* CONFIG_BLK_FILTER */
> +
> +

double blank line

> +static inline void blk_filter_part_add(struct hd_struct *part, dev_t devt)
> +{ };
> +
> +static inline void blk_filter_part_del(struct hd_struct *part)
> +{ };
> +
> +#endif /* CONFIG_BLK_FILTER */
> +
> +#endif
> diff --git a/block/blk-filter.c b/block/blk-filter.c
> new file mode 100644
> index 000000000000..f6de16c45a16
> --- /dev/null
> +++ b/block/blk-filter.c
> @@ -0,0 +1,286 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/genhd.h>
> +#include <linux/bio.h>
> +#include <linux/blkdev.h>
> +#include "blk-filter-internal.h"
> +#include <linux/rwsem.h>
> +
> +

Again here

> +LIST_HEAD(filters);
> +DECLARE_RWSEM(filters_lock);
> +
> +static void blk_filter_release(struct kref *kref)
> +{
> +	struct blk_filter *flt = container_of(kref, struct blk_filter, kref);
> +
> +	kfree(flt);
> +}
> +
> +static inline void blk_filter_get(struct blk_filter *flt)
> +{
> +	kref_get(&flt->kref);
> +}
> +
> +static inline void blk_filter_put(struct blk_filter *flt)
> +{
> +	kref_put(&flt->kref, blk_filter_release);
> +}
> +
> +
> +/**
> + * blk_filter_part_add() - Notify filters when a new partition is added.
> + * @part: The partition for new block device.
> + * @devt: Device id for new block device.
> + *
> + * Description:
> + *    When the block device is appears in the system, call the filter
> + *    callback to notify that the block device appears.
> + */
> +void blk_filter_part_add(struct hd_struct *part, dev_t devt)
> +{
> +	down_read(&filters_lock);
> +	if (!list_empty(&filters)) {
> +		struct list_head *_list_head;
> +
> +		list_for_each(_list_head, &filters) {
> +			void *filter_data;
> +			bool attached = false;
> +			struct blk_filter *flt;
> +
> +			flt = list_entry(_list_head, struct blk_filter, link);
> +
> +			attached = flt->ops->part_add(devt, &filter_data);
> +			if (attached) {
> +				blk_filter_get(flt);
> +				part->filter = flt;
> +				part->filter_data = filter_data;
> +				break;
> +			}
> +		}
> +	}
> +	up_read(&filters_lock);
> +}
> +
> +/**
> + * blk_filter_part_del() - Notify filters when the partition is deleted.
> + * @part: The partition of block device.
> + *
> + * Description:
> + *    When the block device is destroying and the partition is releasing,
> + *    call the filter callback to notify that the block device will be
> + *    deleted.
> + */
> +void blk_filter_part_del(struct hd_struct *part)
> +{
> +	struct blk_filter *flt = part->filter;
> +
> +	if (!flt)
> +		return;
> +
> +	flt->ops->part_del(part->filter_data);
> +
> +	part->filter_data = NULL;
> +	part->filter = NULL;
> +	blk_filter_put(flt);
> +}
> +
> +
> +/**
> + * blk_filter_submit_bio() - Send new bio to filters for processing.
> + * @bio: The new bio for block I/O layer.
> + *
> + * Description:
> + *    This function is an implementation of block layer filter
> + *    interception. If the filter is attached to this block device,
> + *    then bio will be redirected to the filter kernel module.
> + */
> +void blk_filter_submit_bio(struct bio *bio)
> +{
> +	bool intercepted = false;
> +	struct hd_struct *part;
> +
> +	bio_get(bio);
> +
> +	part = disk_get_part(bio->bi_disk, bio->bi_partno);
> +	if (unlikely(!part)) {
> +		bio->bi_status = BLK_STS_IOERR;
> +		bio_endio(bio);
> +
> +		bio_put(bio);
> +		return;
> +	}
> +
> +	down_read(&part->filter_rw_lockup);
> +
> +	if (part->filter)
> +		intercepted = part->filter->ops->filter_bio(bio, part->filter_data);
> +
> +	up_read(&part->filter_rw_lockup);
> +
> +	if (!intercepted)
> +		submit_bio_direct(bio);
> +
> +	disk_put_part(part);
> +
> +	bio_put(bio);
> +}
> +EXPORT_SYMBOL(blk_filter_submit_bio);
> +
> +/**
> + * blk_filter_register() - Register block layer filter.
> + * @ops: New filter callbacks.
> + *
> + * Return:
> + *     Filter ID, a pointer to the service structure of the filter.
> + *
> + * Description:
> + *    Create new filter structure.
> + *    Use blk_filter_attach to attach devices to filter.
> + */
> +void *blk_filter_register(struct blk_filter_ops *ops)
> +{
> +	struct blk_filter *flt;
> +
> +	flt = kzalloc(sizeof(struct blk_filter), GFP_KERNEL);
> +	if (!flt)
> +		return NULL;
> +
> +	kref_init(&flt->kref);
> +	flt->ops = ops;
> +
> +	down_write(&filters_lock);
> +	list_add_tail(&flt->link, &filters);
> +	up_write(&filters_lock);
> +
> +	return flt;
> +}
> +EXPORT_SYMBOL(blk_filter_register);
> +
> +/**
> + * blk_filter_unregister() - Unregister block layer filter.
> + * @filter: filter identifier.
> + *
> + * Description:
> + *    Before call blk_filter_unregister() and unload filter module all
> + *    partitions MUST be detached. Otherwise, the system will have a
> + *    filter with non-existent interception functions.
> + */
> +void blk_filter_unregister(void *filter)
> +{
> +	struct blk_filter *flt = filter;
> +
> +	down_write(&filters_lock);
> +	list_del(&flt->link);
> +	up_write(&filters_lock);
> +
> +	blk_filter_put(flt);
> +}
> +EXPORT_SYMBOL(blk_filter_unregister);
> +
> +/**
> + * blk_filter_attach() - Attach block layer filter.
> + * @devt: The block device identification number.
> + * @filter: Filter identifier.
> + * @filter_data: Specific filters data for this device.
> + *
> + * Return:
> + *    Return code.
> + *    -ENODEV - cannot find this device, it is OK if the device does not exist yet.
> + *    -EALREADY - this device is already attached to this filter.
> + *    -EBUSY - this device is already attached to the another filter.
> + *
> + * Description:
> + *    Attach the device to the block layer filter.
> + *    Only one filter can be attached to a single device.
> + */
> +int blk_filter_attach(dev_t devt, void *filter, void *filter_data)
> +{
> +	int ret = 0;
> +	struct blk_filter *flt = filter;
> +	struct block_device *blk_dev;
> +
> +
> +	blk_dev = bdget(devt);
> +	if (!blk_dev)
> +		return -ENODEV;
> +
> +	blk_filter_freeze(blk_dev);
> +
> +	if (blk_dev->bd_part->filter) {
> +		if (blk_dev->bd_part->filter == flt)
> +			ret = -EALREADY;
> +		else
> +			ret = -EBUSY;
> +	} else {
> +		blk_filter_get(flt);
> +		blk_dev->bd_part->filter = flt;
> +		blk_dev->bd_part->filter_data = filter_data;
> +	}
> +
> +	blk_filter_thaw(blk_dev);
> +
> +	bdput(blk_dev);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(blk_filter_attach);
> +
> +/**
> + * blk_filter_detach() - Detach block layer filter.
> + * @devt: The block device identification number.
> + *
> + * Description:
> + *    Detach the device from the block layer filter.
> + *    Do not forget detach all devices before calling the
> + *    blk_filter_unregister() function and unload the module!
> + */
> +void blk_filter_detach(dev_t devt)
> +{
> +	struct blk_filter *flt;
> +	struct block_device *blk_dev;
> +
> +	blk_dev = bdget(devt);
> +	if (!blk_dev)
> +		return;
> +
> +	blk_filter_freeze(blk_dev);
> +
> +	flt = blk_dev->bd_part->filter;
> +	if (flt) {
> +		blk_dev->bd_part->filter_data = NULL;
> +		blk_dev->bd_part->filter = NULL;
> +		blk_filter_put(flt);
> +	}
> +
> +	blk_filter_thaw(blk_dev);
> +
> +	bdput(blk_dev);
> +}
> +EXPORT_SYMBOL(blk_filter_detach);

All the EXPORT_SYMBOL should probably be EXPORT_SYMBOL_GPL.

> +
> +/**
> + * blk_filter_freeze() - Lock bio submitting.
> + * @bdev: The block device pointer.
> + *
> + * Description:
> + *    Stop bio processing.
> + */
> +void blk_filter_freeze(struct block_device *bdev)
> +{
> +	down_write(&bdev->bd_part->filter_rw_lockup);
> +}
> +EXPORT_SYMBOL(blk_filter_freeze);
> +
> +/**
> + * blk_filter_thaw() - Unlock bio submitting.
> + * @bdev: The block device pointer.
> + *
> + * Description:
> + *    Resume bio processing.
> + */
> +void blk_filter_thaw(struct block_device *bdev)
> +{
> +	up_write(&bdev->bd_part->filter_rw_lockup);
> +}
> +EXPORT_SYMBOL(blk_filter_thaw);
> diff --git a/block/partitions/core.c b/block/partitions/core.c
> index 722406b841df..6b845e98b9a1 100644
> --- a/block/partitions/core.c
> +++ b/block/partitions/core.c
> @@ -11,6 +11,7 @@
>  #include <linux/blktrace_api.h>
>  #include <linux/raid/detect.h>
>  #include "check.h"
> +#include "../blk-filter-internal.h"
>  
>  static int (*check_part[])(struct parsed_partitions *) = {
>  	/*
> @@ -320,9 +321,11 @@ int hd_ref_init(struct hd_struct *part)
>   */
>  void delete_partition(struct gendisk *disk, struct hd_struct *part)
>  {
> -	struct disk_part_tbl *ptbl =
> -		rcu_dereference_protected(disk->part_tbl, 1);
> +	struct disk_part_tbl *ptbl;
> +
> +	blk_filter_part_del(part);
>  
> +	ptbl = rcu_dereference_protected(disk->part_tbl, 1);
>  	/*
>  	 * ->part_tbl is referenced in this part's release handler, so
>  	 *  we have to hold the disk device
> @@ -412,6 +415,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	p->nr_sects = len;
>  	p->partno = partno;
>  	p->policy = get_disk_ro(disk);
> +#ifdef CONFIG_BLK_FILTER
> +	init_rwsem(&p->filter_rw_lockup);
> +#endif
>  
>  	if (info) {
>  		struct partition_meta_info *pinfo;
> @@ -469,6 +475,9 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	/* everything is up and running, commence */
>  	rcu_assign_pointer(ptbl->part[partno], p);
>  
> +	/*inform filter about a new partition*/
> +	blk_filter_part_add(p, devt);
> +
>  	/* suppress uevent if the disk suppresses it */
>  	if (!dev_get_uevent_suppress(ddev))
>  		kobject_uevent(&pdev->kobj, KOBJ_ADD);
> @@ -552,6 +561,7 @@ int bdev_del_partition(struct block_device *bdev, int partno)
>  		goto out_unlock;
>  
>  	sync_blockdev(bdevp);
> +
>  	invalidate_bdev(bdevp);
>  
>  	delete_partition(bdev->bd_disk, part);
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 8ae833e00443..431eae17fd8f 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -237,7 +237,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>  	if (iocb->ki_flags & IOCB_HIPRI)
>  		bio_set_polled(&bio, iocb);
>  
> -	qc = submit_bio(&bio);
> +	qc = submit_bio_direct(&bio);
>  	for (;;) {
>  		set_current_state(TASK_UNINTERRUPTIBLE);
>  		if (!READ_ONCE(bio.bi_private))
> @@ -400,7 +400,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  				polled = true;
>  			}
>  
> -			qc = submit_bio(bio);
> +			qc = submit_bio_direct(bio);
>  
>  			if (polled)
>  				WRITE_ONCE(iocb->ki_cookie, qc);
> @@ -421,7 +421,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>  			atomic_inc(&dio->ref);
>  		}
>  
> -		submit_bio(bio);
> +		submit_bio_direct(bio);
>  		bio = bio_alloc(GFP_KERNEL, nr_pages);
>  	}
>  
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 183299892465..d9bb1b6f6814 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -459,7 +459,7 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
>  		sdio->submit_io(bio, dio->inode, sdio->logical_offset_in_bio);
>  		dio->bio_cookie = BLK_QC_T_NONE;
>  	} else
> -		dio->bio_cookie = submit_bio(bio);
> +		dio->bio_cookie = submit_bio_direct(bio);

All these changes are unnecessary if you reverse things: submit_bio() is kept as
the direct version (as today) and you use a "submit_bio_filtered()" where needed.

>  
>  	sdio->bio = NULL;
>  	sdio->boundary = 0;
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index c1aafb2ab990..e05f20ce8b5f 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -73,7 +73,7 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
>  				file_inode(dio->iocb->ki_filp),
>  				iomap, bio, pos);
>  	else
> -		dio->submit.cookie = submit_bio(bio);
> +		dio->submit.cookie = submit_bio_direct(bio);
>  }
>  
>  static ssize_t iomap_dio_complete(struct iomap_dio *dio)
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index c6d765382926..5b0a32697207 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -10,6 +10,7 @@
>  #include <linux/ioprio.h>
>  /* struct bio, bio_vec and BIO_* flags are defined in blk_types.h */
>  #include <linux/blk_types.h>
> +#include <linux/blk-filter.h>
>  
>  #define BIO_DEBUG
>  
> @@ -411,7 +412,8 @@ static inline struct bio *bio_kmalloc(gfp_t gfp_mask, unsigned int nr_iovecs)
>  	return bio_alloc_bioset(gfp_mask, nr_iovecs, NULL);
>  }
>  
> -extern blk_qc_t submit_bio(struct bio *);
> +extern blk_qc_t submit_bio_direct(struct bio *bio);
> +extern void submit_bio(struct bio *bio);
>  
>  extern void bio_endio(struct bio *);
>  
> diff --git a/include/linux/blk-filter.h b/include/linux/blk-filter.h
> new file mode 100644
> index 000000000000..f3e79e5b4586
> --- /dev/null
> +++ b/include/linux/blk-filter.h
> @@ -0,0 +1,76 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * API declarations for kernel modules utilizing block device filters
> + */
> +
> +#ifndef BLK_FILTER_H
> +#define BLK_FILTER_H
> +
> +#ifdef CONFIG_BLK_FILTER
> +#include <linux/kref.h>
> +
> +struct blk_filter_ops {
> +	/*
> +	 * Intercept bio callback.
> +	 *
> +	 * Returns true if the request was intercepted and placed in the
> +	 * queue for processing. Otherwise submit_bio_direct() calling
> +	 * needed.
> +	 */
> +	bool (*filter_bio)(struct bio *bio, void *filter_data);
> +
> +	/*
> +	 * Callback to a request to add block device to the filter.
> +	 *
> +	 * Returns true if the block device will be filtered.
> +	 * p_filter_data gets a pointer to data that is unique to
> +	 * this device.
> +	 */
> +	bool (*part_add)(dev_t devt, void **p_filter_data);
> +
> +	/*
> +	 * Callback to remove block device from the filter.
> +	 */
> +	void (*part_del)(void *filter_data);
> +};
> +
> +struct blk_filter {
> +	struct list_head link;
> +	struct kref kref;
> +	struct blk_filter_ops *ops;
> +};
> +
> +/*
> + * Register/unregister device to filter
> + */
> +void *blk_filter_register(struct blk_filter_ops *ops);
> +
> +void blk_filter_unregister(void *filter);
> +
> +/*
> + * Attach/detach device to filter
> + */
> +int blk_filter_attach(dev_t devt, void *filter, void *filter_data);
> +
> +void blk_filter_detach(dev_t devt);
> +
> +/*
> + * For a consistent state of the file system use the freeze_bdev/thaw_bdav.
> + * But in addition, to ensure that the filter is not in the state of
> + * intercepting the next BIO, you need to call black_filter_freeze/blk_filter_thaw.
> + * This is especially actual if there is no file system on the disk.
> + */
> +
> +void blk_filter_freeze(struct block_device *bdev);
> +
> +void blk_filter_thaw(struct block_device *bdev);
> +
> +/*
> + * Filters intercept function
> + */
> +void blk_filter_submit_bio(struct bio *bio);
> +
> +#endif /* CONFIG_BLK_FILTER */
> +
> +#endif
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 4ab853461dff..514fab6b947e 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -4,7 +4,7 @@
>  
>  /*
>   * 	genhd.h Copyright (C) 1992 Drew Eckhardt
> - *	Generic hard disk header file by  
> + *	Generic hard disk header file by
>   * 		Drew Eckhardt
>   *
>   *		<drew@...orado.edu>
> @@ -75,6 +75,12 @@ struct hd_struct {
>  	int make_it_fail;
>  #endif
>  	struct rcu_work rcu_work;
> +
> +#ifdef CONFIG_BLK_FILTER
> +	struct rw_semaphore filter_rw_lockup; /* for freezing block device*/
> +	struct blk_filter *filter; /* block layer filter*/
> +	void *filter_data; /*specific for each block device filters data*/
> +#endif
>  };
>  
>  /**
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 01e2858b5fe3..5287346b87a1 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -283,7 +283,7 @@ static int hib_submit_io(int op, int op_flags, pgoff_t page_off, void *addr,
>  		bio->bi_end_io = hib_end_io;
>  		bio->bi_private = hb;
>  		atomic_inc(&hb->count);
> -		submit_bio(bio);
> +		submit_bio_direct(bio);
>  	} else {
>  		error = submit_bio_wait(bio);
>  		bio_put(bio);
> diff --git a/mm/page_io.c b/mm/page_io.c
> index e485a6e8a6cd..4540426400b3 100644
> --- a/mm/page_io.c
> +++ b/mm/page_io.c
> @@ -362,7 +362,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
>  	count_swpout_vm_event(page);
>  	set_page_writeback(page);
>  	unlock_page(page);
> -	submit_bio(bio);
> +	submit_bio_direct(bio);
>  out:
>  	return ret;
>  }
> @@ -434,7 +434,7 @@ int swap_readpage(struct page *page, bool synchronous)
>  	}
>  	count_vm_event(PSWPIN);
>  	bio_get(bio);
> -	qc = submit_bio(bio);
> +	qc = submit_bio_direct(bio);
>  	while (synchronous) {
>  		set_current_state(TASK_UNINTERRUPTIBLE);
>  		if (!READ_ONCE(bio->bi_private))
> 

Separate into multiple patches: one that introduces the filter functions/ops
code and another that changes the block layer where needed.


-- 
Damien Le Moal
Western Digital Research

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