bug#8061: Introduce SEEK_DATA/SEEK_HOLE to extent_scan module

[Paul Eggert]

This email is follow up to <https://bugs.gnu.org/8601> dated 2011-05-01. Jeff,
thanks for reporting the problem. (There's a good chance this email will bounce
but I'll send it to your 2011 email address anyway.)

I recently ran into the same issue and derived the attached patches
independently. I then found your bug report, made sure the attached patches
fixed every problem that your proposal did, and installed the attached patches
into Savannah.

The attached patches 1-3 merely fix typos and refactor.

Patch 4 corresponds to your proposal; however, it differs in that its basic idea
is to use the FIEMAP code only as a fallback if SEEK_DATA doesn't work, rather
than try to add to the already-too-complicated code that fiddles with FIEMAPs.
(I don't observe any significant performance advantage to the FIEMAP stuff, but
maybe that's just me.)

Patch 5 adds opportunistic use of the copy_file_range syscall introduced in
Linux kernel 4.5 (2016) and reworked in 5.3 (2019). This should improve 'cp'
performance on kernels and file systems that support copy_file_range.

0001-maint-typo-fix.patch
Description: Text Data

0002-cp-refactor-extent_copy.patch
Description: Text Data

0003-cp-avoid-copy_reg-goto.patch
Description: Text Data

0004-cp-use-SEEK_DATA-SEEK_HOLE-if-available.patch
Description: Text Data

0005-cp-use-copy_file_range-if-available.patch
Description: Text Data