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    Subject[PATCH v7 0/3] block device interposer
    Date
    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@veeam.com/
    * 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@veeam.com/
    * 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@veeam.com/
    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@veeam.com/
    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@redhat.com.
    * 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@veeam.com/
    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@suse.de/
    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@veeam.com/
    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

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