On Thu, Sep 23, 2021 at 03:41:27PM +0300, Nikolay Borisov wrote:

Kernel has removed support for this feature in 5.7 so let's remove
support from progs as well.

For the record, summary of the discussion.  Removing this is from progs
an libbtrfsutil does not seem to be that critical like the kernel patch,
as eg. strace uses the kernel uapi definition and also does conditional
tests if the macro even exists.

If something is using libbtrfs-devel/ioctl.h, then it should switch to
the kernel uapi but I haven't found any such project.

We may still need to keep some placeholder or comment that the value
used to mean something. We could potentially reuse it in the future, but
there must be some deprecation period.