On Fri, 30 Aug 2019 21:54:43 +0200
Arnd Bergmann [off-list ref] wrote:

On Fri, Aug 30, 2019 at 9:46 PM Michal Suchanek [off-list ref] wrote:

quoted

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/ (local)
Link: https://lore.kernel.org/lkml/20190829214319.498c7de2@naga/ (local)

Signed-off-by: Michal Suchanek <redacted>  

This seems like the right idea in principle.

quoted

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.

AFAICT nds32 never had the syscall. Its headers were added without
__ARCH_WANT_SYS_LLSEEK before the define was removed.

The new architecture csky should be handled.

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.

Yes, that limits the use of __ARCH_WANT_SYS_LLSEEK, does not require
resurrecting the old headers, and may fix some architectures like nds32
that forgot to add it.

Thanks

Michal