This is the only missing part in struct statvfs. The LSB calls [f]statfs() deprecated, and its weird types are definitely off-putting. However, its use is required to get f_type. Instead, allocate one of the six spares to f_type, copied directly from struct statfs. This then becomes a small extension to the standard interface on Linux, instead of two different interfaces, one of which is quite odd due to being an ABI type, and there no longer is any reason to use statfs(). The underlying kernel type is a mess, but all architectures agree on u32 (or more) for the ABI, and all filesystem magicks are 32-bit integers. Since commit 6567db65f495cf7c11f5c1e60a3e54543d5a69bc (prior to 1.0.0), the spare slots have been zero-filled, so on all versions that may be reasonably be encountered in the wild, applications can rely on a nonzero f_type as indication that the new field has been filled in.
the result of the 0xffff mask with the exit status could have bit 15 set, in which case multiplying by 0x10001 overflows 32-bit signed int. making the multiply unsigned avoids the overflow. it also changes the sign extension behavior of the subsequent >> operation, but the affected bits are all unwanted anyway and all discarded by the cast to short.
these badly pollute the namespace with macros whenever _GNU_SOURCE is defined, which is always the case with g++, and especially tends to interfere with C++ constructs. as our implementation of these was macro-only, their removal cannot affect any existing binaries. at the source level, portable software should be prepared for them not to exist. for now, they are left in place with explicit _LARGEFILE64_SOURCE. this provides an easy temporary path for integrators/distributions to get packages building again right away if they break while working on a proper, upstreamable fix. the intent is that this be a very short-term measure and that the macros be removed entirely in the next release cycle.
see linux commit 90f093fa8ea48e5d991332cee160b761423d55c1 rseq, ptrace: Add PTRACE_GET_RSEQ_CONFIGURATION request the struct type got __ prefix to follow existing practice.
see
linux commit 201698626fbca1cf1a3b686ba14cf2a056500716
arm64: Introduce prctl(PR_PAC_{SET,GET}_ENABLED_KEYS)
see linux commit 7fd3253a7de6a317a0683f83739479fb880bffc8 net: Introduce preferred busy-polling linux commit 7c951cafc0cb2e575f1d58677b95ac387ac0a5bd net: Add SO_BUSY_POLL_BUDGET socket option
see linux commit 1446e1df9eb183fdf81c3f0715402f1d7595d4cb kernel: Implement selective syscall userspace redirection linux commit 36a6c843fd0d8e02506681577e96dabd203dd8e8 entry: Use different define for selector variable in SUD redirect syscalls to a userspace handler via SIGSYS, except for a specific range of code. can be toggled via a memory write to a selector variable. mainly for wine.
these are for the aarch64 MTE (memory tagging extension), see linux commit 1c101da8b971a36695319dce7a24711dc567a0dd arm64: mte: Allow user control of the tag check mode via prctl() linux commit af5ce95282dc99d08a27a407a02c763dde1c5558 arm64: mte: Allow user control of the generated random tags via prctl()