Simplify recvmmsg code

[Joseph Myers <joseph at codesourcery dot com>]

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.

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..1a1e1c1 100644
--- a/sysdeps/unix/sysv/linux/recvmmsg.c
+++ b/sysdeps/unix/sysv/linux/recvmmsg.c
@@ -23,71 +23,18 @@
 #include <sys/syscall.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
+}

-- 
Joseph S. Myers
joseph@codesourcery.com