These assertions impose an include order between <linux/fs.h> and
"missing_fs.h", specifically <linux/fs.h> can't be included before
"missing_fs.h". This makes automated include refactoring very painful,
so let's get rid of these assertions and instead assume that linux/fs.h
does the right thing.
To resolve conflict with sys/mount.h and linux/mount.h or linux/fs.h.
The conflict between sys/mount.h and linux/mount.h is resolved in
glibc-2.37 (774058d72942249f71d74e7f2b639f77184160a6), but our baseline
is still glibc-2.31. Also, even with the version or newer, still
sys/mount.h conflicts with linux/fs.h, which is included by
linux/btrfs.h.
This introduces our own implementation of sys/mount.h, that can be
simultaneously included with linux/mount.h and linux/fs.h. This also
imports linux/fs.h, linux/mount.h, and several other dependent headers.
The introduced sys/mount.h header itself may not be enough simple, but
by using the header, we can drop most of workarounds in other source files.
It's great that we provide fallback values, but if we got one of those wrong,
it could be a long time before anyone noticed. So let's add asserts that the
our internal defines actually match the official ones, when the latter are
available.
I did not add '#include "macro.h"' to missing_{audit,capability}, because
those are processed by an awk script that would need additional include
directories and could be confused by the additional lines. We don't include
those headers standalone anyway, so this is not necessary anyway.
The kernel has had filesystem independent reflink ioctls for a
while now, let's try to use them and fall back to the btrfs specific
ones if they're not supported.
Daan De Meyer
Mike Yuan
Yu Watanabe
Lennart Poettering
Zbigniew Jędrzejewski-Szmek
Iago Lopez Galeiras