Re: [PATCH 14/15] arch: add split IPC system calls where needed

Michael Ellerman
2019-01-14T03:40:14Z

Hi Arnd,

Arnd Bergmann <arnd@arndb.de> writes:
> The IPC system call handling is highly inconsistent across architectures,
> some use sys_ipc, some use separate calls, and some use both. We also
> have some architectures that require passing IPC_64 in the flags, and
> others that set it implicitly.
>
> For the additon of a y2083 safe semtimedop() system call, I chose to only
> support the separate entry points, but that requires first supporting
> the regular ones with their own syscall numbers.
>
> The IPC_64 is now implied by the new semctl/shmctl/msgctl system
> calls even on the architectures that require passing it with the ipc()
> multiplexer.
>
> I'm not adding the new semtimedop() or semop() on 32-bit architectures,
> those will get implemented using the new semtimedop_time64() version
> that gets added along with the other time64 calls.
> Three 64-bit architectures (powerpc, s390 and sparc) get semtimedop().
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> One aspect here that might be a bit controversial is the use of
> the same system call numbers across all architectures, synchronizing
> all of them with the x86-32 numbers. With the new syscall.tbl
> files, I hope we can just keep doing that in the future, and no
> longer require the architecture maintainers to assign a number.
>
> This is mainly useful for implementers of the C libraries: if
> we can add future system calls everywhere at the same time, using
> a particular version of the kernel headers also guarantees that
> the system call number macro is visible.
> ---
> arch/m68k/kernel/syscalls/syscall.tbl | 11 +++++++++++
> arch/mips/kernel/syscalls/syscall_o32.tbl | 11 +++++++++++
> arch/powerpc/kernel/syscalls/syscall.tbl | 12 ++++++++++++

I have some changes I'd like to make to our syscall table that will
clash with this.

I'll try and send them today.

> diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
> index db3bbb8744af..1bffab54ff35 100644
> --- a/arch/powerpc/kernel/syscalls/syscall.tbl
> +++ b/arch/powerpc/kernel/syscalls/syscall.tbl
> @@ -425,3 +425,15 @@
> 386 nospu pkey_mprotect sys_pkey_mprotect
> 387 nospu rseq sys_rseq
> 388 nospu io_pgetevents sys_io_pgetevents compat_sys_io_pgetevents
> +# room for arch specific syscalls
> +392 64 semtimedop sys_semtimedop
> +393 common semget sys_semget
> +394 common semctl sys_semctl compat_sys_semctl
> +395 common shmget sys_shmget
> +396 common shmctl sys_shmctl compat_sys_shmctl
> +397 common shmat sys_shmat compat_sys_shmat
> +398 common shmdt sys_shmdt
> +399 common msgget sys_msgget
> +400 common msgsnd sys_msgsnd compat_sys_msgsnd
> +401 common msgrcv sys_msgrcv compat_sys_msgrcv
> +402 common msgctl sys_msgctl compat_sys_msgctl

We already have a gap at 366-377 from when we tried to add the split IPC
calls a few years back.

I guess I don't mind leaving that gap and using the common numbers.

But would be good to add a comment pointing out that we have room there
for arch specific syscalls as well.

cheers