[PATCH v2 0/8] cpio copy-out reflink and chain support

[David Disseldorp]

This patchset adds support for Linux copy_file_range() syscall usage via
a new '--reflink' copy-out parameter. The syscall can considerably
improve archive creation performance and space efficiency on
copy-on-write filesystems such as XFS and Btrfs by performing a metadata
only reflink instead of regular read/write copy I/O. The patchset is
built on Luis' previous submission at:
https://lists.gnu.org/archive/html/bug-cpio/2020-07/msg00001.html

An additional '--chain' parameter is also added for appending a new
archive to an existing file. This is useful for Linux initramfs images,
which can be chained back-to-back.
Unit test coverage for both new parameters is provided.

Dracut changes to make use of the above features when building a Linux
initramfs image have been submitted upstream via:
https://github.com/dracutdevs/dracut/pull/1148 .

This patch set also carries the queued change at
https://savannah.gnu.org/patch/?9263 .

Feedback appreciated.

Changes since v1 (thanks Luis):
- add copy_files_range caller -ENODATA fallback
- add test coverage for sparse files with --reflink
  + I decided against adding back SEEK_DATA / SEEK_HOLE functionality to
    the copy_files_range loop, as seek cursor tracking and error
    handling add significant complexity with little benefit to my
    initramfs generation workload
    - I'll send through the RFC patch I have for the curious

Cheers, David

--

 configure.ac            |   6 +++
 src/copyin.c            |   2 +-
 src/copyout.c           |  43 ++++++++++++++---
 src/extern.h            |   7 ++-
 src/global.c            |   7 ++-
 src/main.c              |  50 ++++++++++++++++++--
 src/mt.c                |   4 +-
 src/util.c              |  65 ++++++++++++++++++++++++--
 tests/chain.at          |  91 ++++++++++++++++++++++++++++++++++++
 tests/reflink-sparse.at |  67 +++++++++++++++++++++++++++
 tests/reflink.at        | 100 ++++++++++++++++++++++++++++++++++++++++
 tests/testsuite.at      |   3 ++
 12 files changed, 426 insertions(+), 19 deletions(-)