Simplify recvmmsg code

  Here is a revised version of the patch that avoids losing the socketcall.h 
#include, so that it actually builds for configurations that use the 
socketcall case (tested build for m68k-linux-gnu).



Simplify recvmmsg code.

Now we can assume a kernel with recvmmsg support, this patch
simplifies the implementation to be similar to that for accept4:
either using socketcall or the syscall according to whether the
syscall is known to be available, without further fallback
implementations.

(In fact further simplification is possible, getting rid of the
__ASSUME_*_SYSCALL_WITH_SOCKETCALL macros now that the minimum kernel
is guaranteed support for all of accept4, recvmmsg, sendmmsg, whether
through syscalls or through socketcall.  I intend to do that for all
of accept4 / recvmmsg / sendmmsg together - so making their
implementations just like those for older socket functions - once the
basic cleanup for 3.2 minimum kernel is done for sendmmsg as well as
recvmmsg.)

Tested for x86_64 and x86.

2017-05-09  Joseph Myers  <joseph@codesourcery.com>

	* sysdeps/unix/sysv/linux/kernel-features.h
	(__ASSUME_RECVMMSG_SYSCALL): Define unconditionally.
	(__ASSUME_RECVMMSG_SOCKETCALL): Remove macro.
	(__ASSUME_RECVMMSG): Likewise.
	* sysdeps/unix/sysv/linux/recvmmsg.c (recvmmsg): Define using
	recvmmsg syscall if it can be assumed to be present, socketcall
	otherwise, with no fallback for runtime failure.
  

On 09/05/2017 12:33, Joseph Myers wrote:
> Here is a revised version of the patch that avoids losing the socketcall.h 
> #include, so that it actually builds for configurations that use the 
> socketcall case (tested build for m68k-linux-gnu).
> 
> 
> 
> Simplify recvmmsg code.
> 
> Now we can assume a kernel with recvmmsg support, this patch
> simplifies the implementation to be similar to that for accept4:
> either using socketcall or the syscall according to whether the
> syscall is known to be available, without further fallback
> implementations.
> 
> (In fact further simplification is possible, getting rid of the
> __ASSUME_*_SYSCALL_WITH_SOCKETCALL macros now that the minimum kernel
> is guaranteed support for all of accept4, recvmmsg, sendmmsg, whether
> through syscalls or through socketcall.  I intend to do that for all
> of accept4 / recvmmsg / sendmmsg together - so making their
> implementations just like those for older socket functions - once the
> basic cleanup for 3.2 minimum kernel is done for sendmmsg as well as
> recvmmsg.)

I was about to work on it, but since you already planning it I will
drop it.

> 
> Tested for x86_64 and x86.
> 
> 2017-05-09  Joseph Myers  <joseph@codesourcery.com>
> 
> 	* sysdeps/unix/sysv/linux/kernel-features.h
> 	(__ASSUME_RECVMMSG_SYSCALL): Define unconditionally.
> 	(__ASSUME_RECVMMSG_SOCKETCALL): Remove macro.
> 	(__ASSUME_RECVMMSG): Likewise.
> 	* sysdeps/unix/sysv/linux/recvmmsg.c (recvmmsg): Define using
> 	recvmmsg syscall if it can be assumed to be present, socketcall
> 	otherwise, with no fallback for runtime failure.

LGTM, thanks.

> 
> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index 74ac627..a5c2263 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -90,13 +90,7 @@
>  
>  /* Support for recvmmsg functionality was added in 2.6.33.  The macros
>     defined correspond to those for accept4.  */
> -#if __LINUX_KERNEL_VERSION >= 0x020621
> -# ifdef __ASSUME_SOCKETCALL
> -#  define __ASSUME_RECVMMSG_SOCKETCALL	1
> -# endif
> -# define __ASSUME_RECVMMSG_SYSCALL	1
> -# define __ASSUME_RECVMMSG	1
> -#endif
> +#define __ASSUME_RECVMMSG_SYSCALL	1
>  
>  /* statfs fills in f_flags since 2.6.36.  */
>  #if __LINUX_KERNEL_VERSION >= 0x020624
> diff --git a/sysdeps/unix/sysv/linux/recvmmsg.c b/sysdeps/unix/sysv/linux/recvmmsg.c
> index 28eb678..de44129 100644
> --- a/sysdeps/unix/sysv/linux/recvmmsg.c
> +++ b/sysdeps/unix/sysv/linux/recvmmsg.c
> @@ -21,73 +21,21 @@
>  
>  #include <sysdep-cancel.h>
>  #include <sys/syscall.h>
> +#include <socketcall.h>
>  #include <kernel-features.h>
>  
> -/* Do not use the recvmmsg syscall on socketcall architectures unless
> -   it was added at the same time as the socketcall support or can be
> -   assumed to be present.  */
> -#if defined __ASSUME_SOCKETCALL \
> -    && !defined __ASSUME_RECVMMSG_SYSCALL_WITH_SOCKETCALL \
> -    && !defined __ASSUME_RECVMMSG_SYSCALL
> -# undef __NR_recvmmsg
> -#endif
> -
> -#ifdef __NR_recvmmsg
> -int
> -recvmmsg (int fd, struct mmsghdr *vmessages, unsigned int vlen, int flags,
> -	  struct timespec *tmo)
> -{
> -  return SYSCALL_CANCEL (recvmmsg, fd, vmessages, vlen, flags, tmo);
> -}
> -#elif defined __NR_socketcall
> -# include <socketcall.h>
> -# ifdef __ASSUME_RECVMMSG_SOCKETCALL
>  int
>  recvmmsg (int fd, struct mmsghdr *vmessages, unsigned int vlen, int flags,
>  	  struct timespec *tmo)
>  {
> +  /* Do not use the recvmmsg syscall on socketcall architectures unless
> +     it was added at the same time as the socketcall support or can be
> +     assumed to be present.  */
> +#if defined __ASSUME_SOCKETCALL \
> +    && !defined __ASSUME_RECVMMSG_SYSCALL_WITH_SOCKETCALL \
> +    && !defined __ASSUME_RECVMMSG_SYSCALL
>    return SOCKETCALL_CANCEL (recvmmsg, fd, vmessages, vlen, flags, tmo);
> -}
> -# else
> -static int have_recvmmsg;
> -
> -int
> -recvmmsg (int fd, struct mmsghdr *vmessages, unsigned int vlen, int flags,
> -	  struct timespec *tmo)
> -{
> -  if (__glibc_likely (have_recvmmsg >= 0))
> -    {
> -      int ret = SOCKETCALL_CANCEL (recvmmsg, fd, vmessages, vlen, flags,
> -				   tmo);
> -      /* The kernel returns -EINVAL for unknown socket operations.
> -	 We need to convert that error to an ENOSYS error.  */
> -      if (__builtin_expect (ret < 0, 0)
> -	  && have_recvmmsg == 0
> -	  && errno == EINVAL)
> -	{
> -	  /* Try another call, this time with an invalid file
> -	     descriptor and all other parameters cleared.  This call
> -	     will not cause any harm and it will return
> -	     immediately.  */
> -	  ret = SOCKETCALL_CANCEL (invalid, -1);
> -	  if (errno == EINVAL)
> -	    {
> -	      have_recvmmsg = -1;
> -	      __set_errno (ENOSYS);
> -	    }
> -	  else
> -	    {
> -	      have_recvmmsg = 1;
> -	      __set_errno (EINVAL);
> -	    }
> -	  return -1;
> -	}
> -      return ret;
> -    }
> -  __set_errno (ENOSYS);
> -  return -1;
> -}
> -# endif /* __ASSUME_RECVMMSG_SOCKETCALL  */
>  #else
> -# include <socket/recvmmsg.c>
> +  return SYSCALL_CANCEL (recvmmsg, fd, vmessages, vlen, flags, tmo);
>  #endif
> +}
>