Simplify accept4, recvmmsg, sendmmsg code

[Adhemerval Zanella]

On 09/05/2017 17:46, Joseph Myers wrote:
> The accept4, recvmmsg and sendmmsg functions had macros
> __ASSUME_*_SYSCALL_WITH_SOCKETCALL.  Before we could assume kernels
> with the relevant functionality, these macros represented the
> conditions under which, on a socketcall architecture, glibc could just
> call the syscall unconditionally and not have to deal with socketcall
> at all for those functions, because if the syscall didn't work for
> them the socketcall call wouldn't either.
> 
> Now we can assume kernels with the relevant functionality, the only
> question is whether we can assume the syscall is present; if not, we
> are on a socketcall architecture and just use socketcall instead.
> Thus, this patch removes the macros that are no longer necessary, and
> simplifies the code for accept4, recvmmsg and sendmmsg to use the same
> logic as the other C implementations of socket functions that may use
> a syscall or socketcall depending on kernel support.
> 
> Tested for x86_64 and x86.

I think we can also now remove mips sendmmsg and recvmmsg implementations
(it does not define __ASSUME_SOCKETCALL, so it should use wire-up calls
as well).

> 
> 2017-05-09  Joseph Myers  <joseph@codesourcery.com>
> 
> 	* sysdeps/unix/sysv/linux/accept4.c (accept4): Use syscall if
> 	[__ASSUME_ACCEPT4_SYSCALL], otherwise socketcall.
> 	* sysdeps/unix/sysv/linux/recvmmsg.c (recvmmsg): Use syscall if
> 	[__ASSUME_RECVMMSG_SYSCALL], otherwise socketcall.
> 	* sysdeps/unix/sysv/linux/sendmmsg.c (__sendmmsg): Use syscall if
> 	[__ASSUME_SENDMMSG_SYSCALL], otherwise socketcall.
> 	* sysdeps/unix/sysv/linux/kernel-features.h
> 	(__ASSUME_ACCEPT4_SYSCALL): Move to general list of macros for
> 	socket syscalls.
> 	(__ASSUME_RECVMMSG_SYSCALL): Likewise.
> 	(__ASSUME_SENDMMSG_SYSCALL): Likewise.
> 	* sysdeps/unix/sysv/linux/i386/kernel-features.h
> 	(__ASSUME_RECVMMSG_SYSCALL_WITH_SOCKETCALL): Remove.
> 	(__ASSUME_SENDMMSG_SYSCALL_WITH_SOCKETCALL): Likewise.
> 	* sysdeps/unix/sysv/linux/microblaze/kernel-features.h
> 	(__ASSUME_RECVMMSG_SYSCALL_WITH_SOCKETCALL): Remove.
> 	* sysdeps/unix/sysv/linux/powerpc/kernel-features.h
> 	(__ASSUME_SENDMMSG_SYSCALL_WITH_SOCKETCALL): Likewise.
> 	* sysdeps/unix/sysv/linux/sh/kernel-features.h
> 	(__ASSUME_SENDMMSG_SYSCALL_WITH_SOCKETCALL): Likewise.
> 	* sysdeps/unix/sysv/linux/sparc/kernel-features.h
> 	(__ASSUME_ACCEPT4_SYSCALL_WITH_SOCKETCALL): Likewise.
> 	(__ASSUME_RECVMMSG_SYSCALL_WITH_SOCKETCALL): Likewise.
> 	(__ASSUME_SENDMMSG_SYSCALL_WITH_SOCKETCALL): Likewise.

LGTM with some one comment remark.

> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index 7728565..76053b5 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -71,16 +71,6 @@
>     2.6.27.  */
>  #define __ASSUME_IN_NONBLOCK	1
>  
> -/* Support for accept4 functionality was added in 2.6.28, but for some
> -   architectures using a separate syscall rather than socketcall that
> -   syscall was only added later, and some architectures first had
> -   socketcall support then a separate syscall.  Define
> -   __ASSUME_ACCEPT4_SYSCALL if it is available through a separate
> -   syscall, and __ASSUME_ACCEPT4_SYSCALL_WITH_SOCKETCALL if it became
> -   available through a separate syscall at the same time as through
> -   socketcall.  */
> -#define __ASSUME_ACCEPT4_SYSCALL	1
> -
>  /* Support for the FUTEX_CLOCK_REALTIME flag was added in 2.6.29.  */
>  #define __ASSUME_FUTEX_CLOCK_REALTIME	1
>  
> @@ -88,18 +78,12 @@
>  #define __ASSUME_PREADV	1
>  #define __ASSUME_PWRITEV	1
>  
> -/* Support for recvmmsg functionality was added in 2.6.33.  The macros
> -   defined correspond to those for accept4.  */
> -#define __ASSUME_RECVMMSG_SYSCALL	1
> -
>  /* statfs fills in f_flags since 2.6.36.  */
>  #if __LINUX_KERNEL_VERSION >= 0x020624
>  # define __ASSUME_STATFS_F_FLAGS	1
>  #endif
>  
> -/* Support for sendmmsg functionality was added in 3.0.  The macros
> -   defined correspond to those for accept4 and recvmmsg.  */
> -#define __ASSUME_SENDMMSG_SYSCALL	1
> +/* Support for sendmmsg functionality was added in 3.0.  */
>  #define __ASSUME_SENDMMSG	1

Since you are there, wouldn't be better to add a comment that we
kept __ASSUME_SENDMMSG because of resolv code instead of kernel
support?