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SubjectRe: [RFC v2 0/4] futex2: Add new futex interface
Hello.

On 09.07.2020 19:59, André Almeida wrote:
> This RFC is a followup to the previous discussion initiated from my
> last
> patch "futex: Implement mechanism to wait on any of several
> futexes"[1].
> As stated in the thread, the correct approach to move forward with the
> wait multiple operation would be to create a new syscall that would
> have
> all new cool features.
>
> The first patch adds the new interface and just translate the call for
> the old interface, without implementing new features. The goal here is
> to establish the interface and to check if everyone is happy with this
> API. The rest of patches are selftests to show the interface in action.
> I have the following questions:
>
> - What suggestions do you have to implement this? Start from scratch or
> reuse the most code possible?
>
> - The interface seems correct and implements the requirements asked by
> you?
>
> Those are the cool new features that this syscall should address some
> day:
>
> - Operate with variable bit size futexes, not restricted to 32:
> 8, 16 and 64
>
> - Wait on multiple futexes, using the following semantics:
>
> struct futex_wait {
> void *uaddr;
> unsigned long val;
> unsigned long flags;
> };
>
> sys_futex_waitv(struct futex_wait *waiters, unsigned int nr_waiters,
> unsigned long flags, struct __kernel_timespec *timo);
>
> - Have NUMA optimizations: if FUTEX_NUMA_FLAG is set, the `void *uaddr`
> argument won't be a value of type u{8, 16, 32, 64} anymore, but a
> struct
> containing a NUMA node hint:
>
> struct futex32_numa {
> u32 value __attribute__ ((aligned (8)));
> u32 hint;
> };
>
> struct futex64_numa {
> u64 value __attribute__ ((aligned (16)));
> u64 hint;
> };
>
> Thanks,
> André
>
> Changes since v1:
> - The timeout argument now uses __kernel_timespec as type
> - time32 interface was removed
> v1: https://lore.kernel.org/patchwork/cover/1255437/
>
> [1] https://lore.kernel.org/patchwork/patch/1194339/
>
> André Almeida (4):
> futex2: Add new futex interface
> selftests: futex: Add futex2 wake/wait test
> selftests: futex: Add futex2 timeout test
> selftests: futex: Add futex2 wouldblock test
>
> MAINTAINERS | 2 +-
> arch/x86/entry/syscalls/syscall_32.tbl | 2 +
> arch/x86/entry/syscalls/syscall_64.tbl | 2 +
> include/linux/syscalls.h | 7 ++
> include/uapi/asm-generic/unistd.h | 8 +-
> include/uapi/linux/futex.h | 10 ++
> init/Kconfig | 7 ++
> kernel/Makefile | 1 +
> kernel/futex2.c | 73 ++++++++++++
> kernel/sys_ni.c | 4 +
> tools/include/uapi/asm-generic/unistd.h | 7 +-
> .../selftests/futex/functional/.gitignore | 1 +
> .../selftests/futex/functional/Makefile | 4 +-
> .../selftests/futex/functional/futex2_wait.c | 111 ++++++++++++++++++
> .../futex/functional/futex_wait_timeout.c | 38 ++++--
> .../futex/functional/futex_wait_wouldblock.c | 33 +++++-
> .../testing/selftests/futex/functional/run.sh | 3 +
> .../selftests/futex/include/futex2test.h | 77 ++++++++++++
> 18 files changed, 373 insertions(+), 17 deletions(-)
> create mode 100644 kernel/futex2.c
> create mode 100644
> tools/testing/selftests/futex/functional/futex2_wait.c
> create mode 100644 tools/testing/selftests/futex/include/futex2test.h

What branch/tag this submission is based on please? It seems it is not a
5.8 but rather 5.7 since the second patch misses faccessat2() syscall
and fails to be applied cleanly.

Thanks.

--
Oleksandr Natalenko (post-factum)

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