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SubjectRe: [PATCH 0/2] block layer filter and block device snapshot module
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On 10/21/20 11:04 AM, Sergei Shtepa wrote:
> Hello everyone! Requesting for your comments and suggestions.
>
> # blk-filter
>
> Block layer filter allows to intercept BIO requests to a block device.
>
> Interception is performed at the very beginning of the BIO request
> processing, and therefore does not affect the operation of the request
> processing queue. This also makes it possible to intercept requests from
> a specific block device, rather than from the entire disk.
>
> The logic of the submit_bio function has been changed - since the
> function execution results are not processed anywhere (except for swap
> and direct-io) the function won't return a value anymore.
>
> Now the submit_bio_direct() function is called whenever the result of
> the blk_qc_t function is required. submit_bio_direct() is not
> intercepted by the block layer filter. This is logical for swap and
> direct-io.
>
> Block layer filter allows you to enable and disable the filter driver on
> the fly. When a new block device is added, the filter driver can start
> filtering this device. When you delete a device, the filter can remove
> its own filter.
>
> The idea of multiple altitudes had to be abandoned in order to simplify
> implementation and make it more reliable. Different filter drivers can
> work simultaneously, but each on its own block device.
>
> # blk-snap
>
> We propose a new kernel module - blk-snap. This module implements
> snapshot and changed block tracking functionality. It is intended to
> create backup copies of any block devices without usage of device mapper.
> Snapshots are temporary and are destroyed after the backup process has
> finished. Changed block tracking allows for incremental and differential
> backup copies.
>
> blk-snap uses block layer filter. Block layer filter provides a callback
> to intercept bio-requests. If a block device disappears for whatever
> reason, send a synchronous request to remove the device from filtering.
>
> blk-snap kernel module is a product of a deep refactoring of the
> out-of-tree kernel veeamsnap kernel module
> (https://github.com/veeam/veeamsnap/):
> * all conditional compilation branches that served for the purpose of
> compatibility with older kernels have been removed;
> * linux kernel code style has been applied;
> * blk-snap mostly takes advantage of the existing kernel code instead of
> reinventing the wheel;
> * all redundant code (such as persistent cbt and snapstore collector)
> has been removed.
>
> Several important things are still have to be done:
> * refactor the module interface for interaction with a user-space code -
> it is already clear that the implementation of some calls can be
> improved.
>
> Your feedback would be greatly appreciated!
>
> Sergei Shtepa (2):
> Block layer filter - second version
> blk-snap - snapshots and change-tracking for block devices
>
> 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 +-
> drivers/block/Kconfig | 2 +
> drivers/block/Makefile | 1 +
> drivers/block/blk-snap/Kconfig | 24 +
> drivers/block/blk-snap/Makefile | 28 +
> drivers/block/blk-snap/big_buffer.c | 193 ++++
> drivers/block/blk-snap/big_buffer.h | 24 +
> drivers/block/blk-snap/blk-snap-ctl.h | 190 ++++
> drivers/block/blk-snap/blk_deferred.c | 566 +++++++++++
> drivers/block/blk-snap/blk_deferred.h | 67 ++
> drivers/block/blk-snap/blk_descr_file.c | 82 ++
> drivers/block/blk-snap/blk_descr_file.h | 26 +
> drivers/block/blk-snap/blk_descr_mem.c | 66 ++
> drivers/block/blk-snap/blk_descr_mem.h | 14 +
> drivers/block/blk-snap/blk_descr_multidev.c | 86 ++
> drivers/block/blk-snap/blk_descr_multidev.h | 25 +
> drivers/block/blk-snap/blk_descr_pool.c | 190 ++++
> drivers/block/blk-snap/blk_descr_pool.h | 38 +
> drivers/block/blk-snap/blk_redirect.c | 507 ++++++++++
> drivers/block/blk-snap/blk_redirect.h | 73 ++
> drivers/block/blk-snap/blk_util.c | 33 +
> drivers/block/blk-snap/blk_util.h | 33 +
> drivers/block/blk-snap/cbt_map.c | 210 +++++
> drivers/block/blk-snap/cbt_map.h | 62 ++
> drivers/block/blk-snap/common.h | 31 +
> drivers/block/blk-snap/ctrl_fops.c | 691 ++++++++++++++
> drivers/block/blk-snap/ctrl_fops.h | 19 +
> drivers/block/blk-snap/ctrl_pipe.c | 562 +++++++++++
> drivers/block/blk-snap/ctrl_pipe.h | 34 +
> drivers/block/blk-snap/ctrl_sysfs.c | 73 ++
> drivers/block/blk-snap/ctrl_sysfs.h | 5 +
> drivers/block/blk-snap/defer_io.c | 397 ++++++++
> drivers/block/blk-snap/defer_io.h | 39 +
> drivers/block/blk-snap/main.c | 82 ++
> drivers/block/blk-snap/params.c | 58 ++
> drivers/block/blk-snap/params.h | 29 +
> drivers/block/blk-snap/rangevector.c | 85 ++
> drivers/block/blk-snap/rangevector.h | 31 +
> drivers/block/blk-snap/snapimage.c | 982 ++++++++++++++++++++
> drivers/block/blk-snap/snapimage.h | 16 +
> drivers/block/blk-snap/snapshot.c | 225 +++++
> drivers/block/blk-snap/snapshot.h | 17 +
> drivers/block/blk-snap/snapstore.c | 929 ++++++++++++++++++
> drivers/block/blk-snap/snapstore.h | 68 ++
> drivers/block/blk-snap/snapstore_device.c | 532 +++++++++++
> drivers/block/blk-snap/snapstore_device.h | 63 ++
> drivers/block/blk-snap/snapstore_file.c | 52 ++
> drivers/block/blk-snap/snapstore_file.h | 15 +
> drivers/block/blk-snap/snapstore_mem.c | 91 ++
> drivers/block/blk-snap/snapstore_mem.h | 20 +
> drivers/block/blk-snap/snapstore_multidev.c | 118 +++
> drivers/block/blk-snap/snapstore_multidev.h | 22 +
> drivers/block/blk-snap/tracker.c | 449 +++++++++
> drivers/block/blk-snap/tracker.h | 38 +
> drivers/block/blk-snap/tracking.c | 270 ++++++
> drivers/block/blk-snap/tracking.h | 13 +
> drivers/block/blk-snap/version.h | 7 +
> 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 +-
> 70 files changed, 9074 insertions(+), 26 deletions(-)
> create mode 100644 block/blk-filter-internal.h
> create mode 100644 block/blk-filter.c
> create mode 100644 drivers/block/blk-snap/Kconfig
> create mode 100644 drivers/block/blk-snap/Makefile
> create mode 100644 drivers/block/blk-snap/big_buffer.c
> create mode 100644 drivers/block/blk-snap/big_buffer.h
> create mode 100644 drivers/block/blk-snap/blk-snap-ctl.h
> create mode 100644 drivers/block/blk-snap/blk_deferred.c
> create mode 100644 drivers/block/blk-snap/blk_deferred.h
> create mode 100644 drivers/block/blk-snap/blk_descr_file.c
> create mode 100644 drivers/block/blk-snap/blk_descr_file.h
> create mode 100644 drivers/block/blk-snap/blk_descr_mem.c
> create mode 100644 drivers/block/blk-snap/blk_descr_mem.h
> create mode 100644 drivers/block/blk-snap/blk_descr_multidev.c
> create mode 100644 drivers/block/blk-snap/blk_descr_multidev.h
> create mode 100644 drivers/block/blk-snap/blk_descr_pool.c
> create mode 100644 drivers/block/blk-snap/blk_descr_pool.h
> create mode 100644 drivers/block/blk-snap/blk_redirect.c
> create mode 100644 drivers/block/blk-snap/blk_redirect.h
> create mode 100644 drivers/block/blk-snap/blk_util.c
> create mode 100644 drivers/block/blk-snap/blk_util.h
> create mode 100644 drivers/block/blk-snap/cbt_map.c
> create mode 100644 drivers/block/blk-snap/cbt_map.h
> create mode 100644 drivers/block/blk-snap/common.h
> create mode 100644 drivers/block/blk-snap/ctrl_fops.c
> create mode 100644 drivers/block/blk-snap/ctrl_fops.h
> create mode 100644 drivers/block/blk-snap/ctrl_pipe.c
> create mode 100644 drivers/block/blk-snap/ctrl_pipe.h
> create mode 100644 drivers/block/blk-snap/ctrl_sysfs.c
> create mode 100644 drivers/block/blk-snap/ctrl_sysfs.h
> create mode 100644 drivers/block/blk-snap/defer_io.c
> create mode 100644 drivers/block/blk-snap/defer_io.h
> create mode 100644 drivers/block/blk-snap/main.c
> create mode 100644 drivers/block/blk-snap/params.c
> create mode 100644 drivers/block/blk-snap/params.h
> create mode 100644 drivers/block/blk-snap/rangevector.c
> create mode 100644 drivers/block/blk-snap/rangevector.h
> create mode 100644 drivers/block/blk-snap/snapimage.c
> create mode 100644 drivers/block/blk-snap/snapimage.h
> create mode 100644 drivers/block/blk-snap/snapshot.c
> create mode 100644 drivers/block/blk-snap/snapshot.h
> create mode 100644 drivers/block/blk-snap/snapstore.c
> create mode 100644 drivers/block/blk-snap/snapstore.h
> create mode 100644 drivers/block/blk-snap/snapstore_device.c
> create mode 100644 drivers/block/blk-snap/snapstore_device.h
> create mode 100644 drivers/block/blk-snap/snapstore_file.c
> create mode 100644 drivers/block/blk-snap/snapstore_file.h
> create mode 100644 drivers/block/blk-snap/snapstore_mem.c
> create mode 100644 drivers/block/blk-snap/snapstore_mem.h
> create mode 100644 drivers/block/blk-snap/snapstore_multidev.c
> create mode 100644 drivers/block/blk-snap/snapstore_multidev.h
> create mode 100644 drivers/block/blk-snap/tracker.c
> create mode 100644 drivers/block/blk-snap/tracker.h
> create mode 100644 drivers/block/blk-snap/tracking.c
> create mode 100644 drivers/block/blk-snap/tracking.h
> create mode 100644 drivers/block/blk-snap/version.h
> create mode 100644 include/linux/blk-filter.h
>
> --
> 2.20.1
>
I do understand where you are coming from, but then we already have a
dm-snap which does exactly what you want to achieve.
Of course, that would require a reconfiguration of the storage stack on
the machine, which is not always possible (or desired).

What I _could_ imagine would be a 'dm-intercept' thingie, which
redirects the current submit_bio() function for any block device, and
re-routes that to a linear device-mapper device pointing back to the
original block device.

That way you could attach it to basically any block device, _and_ can
use the existing device-mapper functionality to do fancy stuff once the
submit_io() callback has been re-routed.

And it also would help in other scenarios, too; with such a
functionality we could seamlessly clone devices without having to move
the whole setup to device-mapper first.

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer

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