selftests/core: test CLOSE_RANGE_EXCEPT

Cover the inverted range:

- with plain close the window stays and everything outside of it goes,
  stdio included

- a window at the top, one that cannot hold a descriptor and one of a
  single descriptor keep just what they name, and so does the unshare
  form on a table that is not shared

- with CLOSE_RANGE_CLOEXEC everything outside of the window is marked
  and the window is not, in place and in a clone, for a
  window in the middle, at the bottom, at the top and above the table

- with CLOSE_RANGE_UNSHARE the table the child cloned from is untouched,
  a window near the top of the table comes back whole, one at the bottom
  keeps stdio, one that cannot hold a descriptor keeps nothing, and the
  slots left behind are handed out again from the bottom

- the bounds are checked before the range is turned around

The extra cases came out of walking the window positions that
__range_close(), __range_cloexec() and dup_fd() tell apart: at the
bottom, in the middle, at the top, above the table, a single descriptor
and none, on a shared and on a private table.

Link: https://patch.msgid.link/20260921-work-file-close_range_except-v1-7-c20d0b49270d@kernel.org
Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions