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Date:   Sat, 20 Jul 2019 22:40:49 +0200
From:   Arnd Bergmann <>
To:     Florian Weimer <>
Cc:     Sergei Trofimovich <>,
        Networking <>,
        Linux Kernel Mailing List <>,
        GNU C Library <>,
        "David S. Miller" <>,
        Michael Kerrisk <>,
        linux-man <>
Subject: Re: linux-headers-5.2 and proper use of SIOCGSTAMP

On Sat, Jul 20, 2019 at 9:34 PM Florian Weimer <> wrote:
> * Arnd Bergmann:
> > On Sat, Jul 20, 2019 at 8:10 PM Florian Weimer <> wrote:
> > As far as I can tell, nobody thought it would be a problem to move it
> > from asm/sockios.h to linux/sockios.h, as the general rule is that one
> > should use the linux/*.h version if both exist, and that the asm/*.h
> > version only contains architecture specific definitions. The new
> > definition is the same across all architectures, so it made sense to
> > have it in the common file.
> Most of the socket-related constants are not exposed in UAPI headers,
> although userspace is expected to use them.  It seems to me that due
> to the lack of other options among the UAPI headers, <asm/socket.h>
> has been a dumping ground for various socket-related things in the
> past, whether actually architecture-specific or not.
> <linux/socket.h> does not include <asm/socket.h>, so that's why we
> usually end up with including <asm/socket.h> (perhaps indirectly via
> <sys/socket.h>), which used to include <asm/sockios.h> on most (all?)
> architectures.  That in turn provided some of the SIOC* constants in
> the past, so people didn't investigate other options.

It seems that both the missing constants and the fact that
linux/socket.h doesn't include asm/socket.h and linux/sockios.h
goes back to a 21 year old commit:

commit 74f513101058f7585176ea8cdf6fb026faea8a7e
Author: linus1 <>
Date:   Wed May 20 11:00:00 1998 -0800

    [tytso] include/asm-i386/posix_types.h
    This quick fix eliminates a lot of warning messages when
    compiling e2fsprogs under glibc.  This is because the glibc header files
    defines its own version of FD_SET, FD_ZERO, etc., and so if you need to
    #include the kernel include files, you get a lot of duplicate defined
    macro warning messages.  This patch simply #ifdef's out the kernel
    versions of these function if the kernel is not being compiled and the
    glibc header files are in use.

diff --git a/include/linux/socket.h b/include/linux/socket.h
index 08f0d281401c..35a7629b6b70 100644
--- a/include/linux/socket.h
+++ b/include/linux/socket.h
@@ -1,6 +1,8 @@
 #ifndef _LINUX_SOCKET_H
 #define _LINUX_SOCKET_H

+#if defined(__KERNEL__) || !defined(__GLIBC__) || (__GLIBC__ < 2)
 #include <asm/socket.h>                        /* arch-dependent
defines       */
 #include <linux/sockios.h>             /* the SIOCxxx I/O controls     */
 #include <linux/uio.h>                 /* iovec support                */
@@ -256,4 +258,5 @@ extern int move_addr_to_user(void *kaddr, int
klen, void *uaddr, int *ulen);
 extern int move_addr_to_kernel(void *uaddr, int ulen, void *kaddr);
 extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data);
+#endif /* not kernel and not glibc */
 #endif /* _LINUX_SOCKET_H */

(the same commit did similar changes in linux/stat.h and asm/posix_types.h)

Over time, the check for glibc was removed (to allow including linux/socket.h
before sys/socket.h), and all the #ifdef __KERNEL__ bits were removed
from the installed header as part of the uapi header split.

> I think we can change glibc to include <linux/sockios.h> in addition
> to <asm/socket.h>.  <linux/sockios.h> looks reasonably clean to me,
> much better than <asm/socket.h>.

That seems reasonable to me, but overall my fear is that these headers
are already so broken that any change will risk breaking something
in more or less unexpected ways.


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