[PATCH] Revert "asm-generic: Remove unneeded __ARCH_WANT_SYS_LLSEEK macro"

[Arnd Bergmann]

On Fri, Aug 30, 2019 at 9:46 PM Michal Suchanek <msuchanek at suse.de> wrote:
>
> This reverts commit caf6f9c8a326cffd1d4b3ff3f1cfba75d159d70b.
>
> Maybe it was needed after all.
>
> When CONFIG_COMPAT is disabled on ppc64 the kernel does not build.
>
> There is resistance to both removing the llseek syscall from the 64bit
> syscall tables and building the llseek interface unconditionally.
>
> Link: https://lore.kernel.org/lkml/20190828151552.GA16855@infradead.org/
> Link: https://lore.kernel.org/lkml/20190829214319.498c7de2@naga/
>
> Signed-off-by: Michal Suchanek <msuchanek at suse.de>

This seems like the right idea in principle.

> index 5bbf587f5bc1..2f3c4bb138c4 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -331,7 +331,7 @@ COMPAT_SYSCALL_DEFINE3(lseek, unsigned int, fd, compat_off_t, offset, unsigned i
>  }
>  #endif
>
> -#if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT)
> +#ifdef __ARCH_WANT_SYS_LLSEEK
>  SYSCALL_DEFINE5(llseek, unsigned int, fd, unsigned long, offset_high,
>                 unsigned long, offset_low, loff_t __user *, result,
>                 unsigned int, whence)

However, only reverting the patch will now break all newly added
32-bit architectures that don't define __ARCH_WANT_SYS_LLSEEK:
at least nds32 and riscv32 come to mind, not sure if there is another.

I think the easiest way however would be to combine the two checks
above and make it

#if !defined(CONFIG_64BIT) || defined(CONFIG_COMPAT) ||
defined(__ARCH_WANT_SYS_LLSEEK)

and then only set __ARCH_WANT_SYS_LLSEEK for powerpc.

     Arnd