Hi all.
I'm joyful to suggest the block device interposer (bdev_interposer) v7.
bdev_interposer allows to redirect bio requests to other block devices.
In this series of patches I suggest a different implementation of the bio
interception mechanism. Now the interposer is a different block device.
Instead of an additional hook, the function fops->submit_bio() of
the interposer device is used.
This implementation greatly simplifies the application of this
bdev_interposer in device-mapper. But there is one limitation - the size
of the interposer device must be greater than or equal to the size of
the original device.
The first patch adds the function blk_mq_is_queue_frozen(). It allows to
check a queue state.
The second patch is dedicated to bdev_interposer itself, which provides
the ability to redirect bio to the interposer device.
The third one adds the DM_INTERPOSED_FLAG flag. When this flag is
applied with the ioctl DM_TABLE_LOAD_CMD, the underlying devices are
opened without the FMODE_EXCL flag and connected via bdev_interposer.
Changes in this patchset v7:
* the request interception mechanism. Now the interposer is
a block device that receives requests instead of the original device;
* code design fixes.
History:
v6 - https://patchwork.kernel.org/project/linux-block/cover/1614774618-22410-1-git-send-email-sergei.shtepa@xxxxxxxxx/
* designed for 5.12;
* thanks to the new design of the bio structure in v5.12, it is
possible to perform interception not for the entire disk, but
for each block device;
* instead of the new ioctl DM_DEV_REMAP_CMD and the 'noexcl' option,
the DM_INTERPOSED_FLAG flag for the ioctl DM_TABLE_LOAD_CMD is
applied.
v5 - https://patchwork.kernel.org/project/linux-block/cover/1612881028-7878-1-git-send-email-sergei.shtepa@xxxxxxxxx/
* rebase for v5.11-rc7;
* patch set organization;
* fix defects in documentation;
* add some comments;
* change mutex names for better code readability;
* remove calling bd_unlink_disk_holder() for targets with non-exclusive
flag;
* change type for struct dm_remap_param from uint8_t to __u8.
v4 - https://patchwork.kernel.org/project/linux-block/cover/1612367638-3794-1-git-send-email-sergei.shtepa@xxxxxxxxx/
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 (3):
block: add blk_mq_is_queue_frozen()
block: add bdev_interposer
dm: add DM_INTERPOSED_FLAG
block/bio.c | 2 ++
block/blk-core.c | 57 ++++++++++++++++++++++++++++++++
block/blk-mq.c | 13 ++++++++
block/genhd.c | 54 +++++++++++++++++++++++++++++++
drivers/md/dm-core.h | 3 ++
drivers/md/dm-ioctl.c | 13 ++++++++
drivers/md/dm-table.c | 61 +++++++++++++++++++++++++++++------
drivers/md/dm.c | 38 +++++++++++++++-------
include/linux/blk-mq.h | 1 +
include/linux/blk_types.h | 3 ++
include/linux/blkdev.h | 9 ++++++
include/linux/device-mapper.h | 1 +
include/uapi/linux/dm-ioctl.h | 6 ++++
13 files changed, 240 insertions(+), 21 deletions(-)
--
2.20.1
