[glibc] linux: Extend internal clone3 documentation

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2fe58919a0bfd1064c59120520116237ba818ed3

commit 2fe58919a0bfd1064c59120520116237ba818ed3
Author: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Date:   Thu Jan 12 10:58:49 2023 -0300

    linux: Extend internal clone3 documentation
    
    Different than kernel, clone3 returns EINVAL for NULL struct
    clone_args or function pointer.  This is similar to clone
    interface that return EINVAL for NULL function argument.
    
    It also clean up the Linux clone3.h interface, since it not
    currently exported.
    
    Checked on x86_64-linux-gnu.
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 include/clone_internal.h         | 24 +++++++++++++++++++-----
 sysdeps/unix/sysv/linux/clone3.h | 10 +---------
 2 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/include/clone_internal.h b/include/clone_internal.h
index 4b23ef33ce..73b8114df4 100644
--- a/include/clone_internal.h
+++ b/include/clone_internal.h
@@ -1,10 +1,24 @@
-#ifndef _CLONE3_H
-#include_next <clone3.h>
+#ifndef _CLONE_INTERNAL_H
+#define _CLONE_INTERNAL_H
 
-extern __typeof (clone3) __clone3;
+#include <clone3.h>
 
-/* The internal wrapper of clone/clone2 and clone3.  If __clone3 returns
-   -1 with ENOSYS, fall back to clone or clone2.  */
+/* The clone3 syscall provides a superset of the functionality of the clone
+   interface.  The kernel might extend __CL_ARGS struct in the future, with
+   each version with a diffent __SIZE.  If the child is created, it will
+   start __FUNC function with __ARG arguments.
+
+   Different than kernel, the implementation also returns EINVAL for an
+   invalid NULL __CL_ARGS or __FUNC (similar to __clone).
+
+   This function is only implemented if the ABI defines HAVE_CLONE3_WRAPPER.
+*/
+extern int __clone3 (struct clone_args *__cl_args, size_t __size,
+		     int (*__func) (void *__arg), void *__arg);
+
+/* The internal wrapper of clone/clone2 and clone3.  Different than __clone3,
+   it will align the stack if required.  If __clone3 returns -1 with ENOSYS,
+   fall back to clone or clone2.  */
 extern int __clone_internal (struct clone_args *__cl_args,
 			     int (*__func) (void *__arg), void *__arg);
 
diff --git a/sysdeps/unix/sysv/linux/clone3.h b/sysdeps/unix/sysv/linux/clone3.h
index 42055ea981..e4d642e521 100644
--- a/sysdeps/unix/sysv/linux/clone3.h
+++ b/sysdeps/unix/sysv/linux/clone3.h
@@ -1,4 +1,4 @@
-/* The wrapper of clone3.
+/* The clone3 kernel interface definitions.
    Copyright (C) 2021-2023 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
@@ -23,8 +23,6 @@
 #include <stddef.h>
 #include <bits/types.h>
 
-__BEGIN_DECLS
-
 /* The unsigned 64-bit and 8-byte aligned integer type.  */
 typedef __U64_TYPE __aligned_uint64_t __attribute__ ((__aligned__ (8)));
 
@@ -58,10 +56,4 @@ struct clone_args
   __aligned_uint64_t cgroup;
 };
 
-/* The wrapper of clone3.  */
-extern int clone3 (struct clone_args *__cl_args, size_t __size,
-		   int (*__func) (void *__arg), void *__arg);
-
-__END_DECLS
-
 #endif /* clone3.h */