[PATCH 1/2] misc: Set generic pselect as ENOSYS

[Joseph Myers]

On Thu, 14 Nov 2019, Adhemerval Zanella wrote:

> The generic pselect implementation has the very specific race condition
> that motived the creation of the pselect syscall (no atomicity in
> signal mask set/reset).  Using it as generic implementation is
> counterproductive  Also currently only microblaze uses it as fallback
> when used on kernel prior 3.15.
> 
> This patch moves the generic implementation to a microblaze specific
> one, sets the generic internal as a ENOSYS, and cleanups the Linux
> generic implementation.
> 
> Also, the microblaze generic implementation first try to issue
> pselect instead of use the fallback (since it is expect that if
> the microblaze usage does rely on pselect, a sufficient updated
> kernel will be used).  Microblaze defines __NR_pselect6 for Linux
> v3.2, although it was only wire-up on v3.15 (and the syscall number
> is the same as previous defined).

I'll raise the same issue here I raise whenever someone proposes having 
fallback code for old kernels without a corresponding __ASSUME_* macro.

We need a simple and uniform way, when increasing the minimum kernel 
version, to find all the fallback code that can be removed.  That means 
__ASSUME_* macros in kernel-features.h based on __LINUX_KERNEL_VERSION.  
A free-form text comment mentioning "3.15" is no good for that purpose as 
there is no sensible automated way to find all such comments when 
increasing the minimum from 3.2 to 4.4 (for example, as the next such 
increase that seems to make sense in terms of the cleanups it enables).

-- 
Joseph S. Myers
joseph@codesourcery.com