Hi all. I'm ready to suggest the block-layer interposer (blk_interposer). blk_interposer allows to intercept bio requests, remap bio to another devices or add new bios. This patch series adds support blk_interposer for dm-linear. In the first patch, I suggest the remap_and_filter.rst file. Yes, Mike, it's probably too early for documentation, but maybe it will be interesting for someone. In the documentation I tried to explain the purpose of blk_interposer and what prospects it opens up. The second patch is dedicated to blk_interposer itself, which provides the ability to intercept bio. The third - adds the function blk_mq_is_queue_frozen(). It allows to assert a queue state. The fourth one adds support for blk_interposer from the device mapper. Added ioctl DM_DEV_REMAP_CMD. In the fifth - added the 'noexcl' option for dm-linear, which allows to open the underlying block-device without the FMODE_EXCL mode. This allows to create a dm device to which can redirect bio requests using DM_DEV_REMAP_CMD. Here I would like to discuss the implementation. I don't like to play with flags. Adding the non_exclusive flags creates an excessive complexity. An alternative solution is to explicitly specify the FMODE_EXCL mode for each dm-target. The problem is that in this case, we will have to change each dm-target. It doesn't look cool either. The latest patch changes linear.rst with the description of the 'noexcl' option that is added for dm-linear. A little history of changes: v4 - current patch set Mostly changes were made, due to Damien's comments: * on the design of the code; * by the patch set organization; * bug with passing a wrong parameter to dm_get_device(); * description of the 'noexcl' parameter in the linear.rst. Also added remap_and_filter.rst. v3 - https://patchwork.kernel.org/project/linux-block/cover/1611853955-32167-1-git-send-email-sergei.shtepa@xxxxxxxxx/ In this version, I already suggested blk_interposer to apply to dm-linear. Problems were solved: * Interception of bio requests from a specific device on the disk, not from the entire disk. To do this, we added the dm_interposed_dev structure and an interval tree to store these structures. * Implemented ioctl DM_DEV_REMAP_CMD. A patch with changes in the lvm2 project was sent to the team lvm-devel@xxxxxxxxxx. * Added the 'noexcl' option for dm-linear, which allows you to open the underlying block-device without FMODE_EXCL mode. v2 - https://patchwork.kernel.org/project/linux-block/cover/1607518911-30692-1-git-send-email-sergei.shtepa@xxxxxxxxx/ I tried to suggest blk_interposer without using it in device mapper, but with the addition of a sample of its use. It was then that I learned about the maintainers' attitudes towards the samples directory :). v1 - https://lwn.net/ml/linux-block/20201119164924.74401-1-hare@xxxxxxx/ This Hannes's patch can be considered as a starting point, since this is where the interception mechanism and the term blk_interposer itself appeared. It became clear that blk_interposer can be useful for device mapper. before v1 - https://patchwork.kernel.org/project/linux-block/cover/1603271049-20681-1-git-send-email-sergei.shtepa@xxxxxxxxx/ I tried to offer a rather cumbersome blk-filter and a monster-like blk-snap module for creating snapshots. Thank you to everyone who was able to take the time to review the previous versions. I hope that this time I achieved the required quality. Thanks, Sergei. Sergei Shtepa (6): docs: device-mapper: add remap_and_filter block: add blk_interposer block: add blk_mq_is_queue_frozen() dm: new ioctl DM_DEV_REMAP_CMD dm: add 'noexcl' option for dm-linear docs: device-mapper: 'noexcl' option for dm-linear .../admin-guide/device-mapper/index.rst | 1 + .../admin-guide/device-mapper/linear.rst | 26 +- .../device-mapper/remap_and_filter.rst | 132 ++++++ block/bio.c | 2 + block/blk-core.c | 33 ++ block/blk-mq.c | 13 + block/genhd.c | 82 ++++ drivers/md/dm-core.h | 20 + drivers/md/dm-ioctl.c | 39 ++ drivers/md/dm-linear.c | 14 +- drivers/md/dm-table.c | 12 +- drivers/md/dm.c | 400 +++++++++++++++++- drivers/md/dm.h | 2 +- include/linux/blk-mq.h | 1 + include/linux/blk_types.h | 6 +- include/linux/device-mapper.h | 7 + include/linux/genhd.h | 18 + include/uapi/linux/dm-ioctl.h | 15 +- 18 files changed, 792 insertions(+), 31 deletions(-) create mode 100644 Documentation/admin-guide/device-mapper/remap_and_filter.rst -- 2.20.1
