[RFC PATCH 0/7] Allow race-free block device handling

[Demi Marie Obenour <demi@invisiblethingslab.com>]

This work aims to allow userspace to create and destroy block devices
in a race-free and leak-free way, and to allow them to be exposed to
other Xen VMs via blkback without leaks or races.  It’s marked as RFC
for a few reasons:

- The code has been only lightly tested.  It might be unstable or
  insecure.

- The DM_DEV_CREATE ioctl gains a new flag.  Unknown flags were
  previously ignored, so this could theoretically break buggy userspace
  tools.

- I have no idea if I got the block device reference counting and
  locking correct.

Demi Marie Obenour (7):
  block: Support creating a struct file from a block device
  Allow userspace to get an FD to a newly-created DM device
  Implement diskseq checks in blkback
  Increment diskseq when releasing a loop device
  If autoclear is set, delete a no-longer-used loop device
  Minor blkback cleanups
  xen/blkback: Inform userspace that device has been opened

 block/bdev.c                        |  77 +++++++++++--
 block/genhd.c                       |   1 +
 drivers/block/loop.c                |  17 ++-
 drivers/block/xen-blkback/blkback.c |   8 +-
 drivers/block/xen-blkback/xenbus.c  | 171 ++++++++++++++++++++++------
 drivers/md/dm-ioctl.c               |  67 +++++++++--
 include/linux/blkdev.h              |   5 +
 include/uapi/linux/dm-ioctl.h       |  16 ++-
 8 files changed, 298 insertions(+), 64 deletions(-)

-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab