[PATCH v2 0/6] unshare: Add support for mapping ranges of user/group IDs

[Sean Anderson <seanga2@gmail.com>]

This series adds support for mapping ranges of user/group IDs using the
newuidmap and newgidmap programs from shadow. The intent is to allow
for root-less bootstrapping of Linux root filesystems with correct
ownership. My primary inspiration is mmdebstrap [1], which uses
unshare(2) to create Debian root filesystems without needing root
access.

[1] https://gitlab.mister-muffin.de/josch/mmdebstrap

Changes in v2:
- Add "auto" option for --map-users and --map-groups
- Add UID_BUFSIZ macro to hold the maximum size of a uid represented as
  a string
- Add some documentation for waitchild
- Add some helpers for forking and synchronizing
- Copy names from string_to_idarray into a buffer to add a
  nul-terminator, instead of modifying them directly
- Document new "auto" value for --map-user and --map-group
- Fix most of read_subid_range using spaces instead of tabs
- Fix typo of --group instead of --user
- Update doc comments for uint_to_id() and get_map_range()
- Use more meaningful numbers in map_ids
- Use pathname macros for /etc/sub{u,g}id
- Use sync helpers for idmap

Sean Anderson (6):
  include/c: Add abs_diff macro
  unshare: Add waitchild helper
  unshare: Add some helpers for forking and synchronizing
  unshare: Add options to map blocks of user/group IDs
  unshare: Add option to automatically create user and group maps
  unshare: Document --map-{groups,users,auto}

 include/c.h              |   8 +
 include/pathnames.h      |   3 +
 sys-utils/unshare.1.adoc |  32 +++
 sys-utils/unshare.c      | 477 ++++++++++++++++++++++++++++++++++-----
 4 files changed, 465 insertions(+), 55 deletions(-)

-- 
2.33.0