[PATCH] Linux: Implement opensock using Netlink sockets

[fweimer at redhat dot com (Florian Weimer)]

inet/tst-inet6_scopeid_pton uses __opensock indirectly, to call ioctl
with SIOCGIFINDEX, and it still works after this change.

2018-06-18  Florian Weimer  <fweimer@redhat.com>

	* sysdeps/unix/sysv/linux/opensock.c (__opensock): Unconditionally
	return a Netlink socket.
	* sysdeps/unix/sysv/linux/s390/opensock.c: Remove file.

diff --git a/sysdeps/unix/sysv/linux/opensock.c b/sysdeps/unix/sysv/linux/opensock.c
index fd9445bc3b..f5d7322c35 100644
--- a/sysdeps/unix/sysv/linux/opensock.c
+++ b/sysdeps/unix/sysv/linux/opensock.c
@@ -15,100 +15,15 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <assert.h>
-#include <errno.h>
-#include <stdio.h>
-#include <string.h>
-#include <unistd.h>
 #include <sys/socket.h>
+#include <linux/netlink.h>
 
 /* Return a socket of any type.  The socket can be used in subsequent
    ioctl calls to talk to the kernel.  */
 int
 __opensock (void)
 {
-  static int last_family;	/* Available socket family we will use.  */
-  static int last_type;
-  static const struct
-  {
-    int family;
-    const char procname[15];
-  } afs[] =
-    {
-      { AF_UNIX, "net/unix" },
-      { AF_INET, "" },
-      { AF_INET6, "net/if_inet6" },
-      { AF_AX25, "net/ax25" },
-      { AF_NETROM, "net/nr" },
-      { AF_ROSE, "net/rose" },
-      { AF_IPX, "net/ipx" },
-      { AF_APPLETALK, "net/appletalk" },
-      { AF_ECONET, "sys/net/econet" },
-      { AF_ASH, "sys/net/ash" },
-      { AF_X25, "net/x25" },
-#ifdef NEED_AF_IUCV
-      { AF_IUCV, "net/iucv" }
-#endif
-    };
-#define nafs (sizeof (afs) / sizeof (afs[0]))
-  char fname[sizeof "/proc/" + 14];
-  int result;
-  int has_proc;
-  size_t cnt;
-
-  /* We already know which family to use from the last call.  Use it
-     again.  */
-  if (last_family != 0)
-    {
-      assert (last_type != 0);
-
-      result = __socket (last_family, last_type | SOCK_CLOEXEC, 0);
-      if (result != -1 || errno != EAFNOSUPPORT)
-	/* Maybe the socket type isn't supported anymore (module is
-	   unloaded).  In this case again try to find the type.  */
-	return result;
-
-      /* Reset the values.  They seem not valid anymore.  */
-      last_family = 0;
-      last_type = 0;
-    }
-
-  /* Check whether the /proc filesystem is available.  */
-  has_proc = __access ("/proc/net", R_OK) != -1;
-  strcpy (fname, "/proc/");
-
-  /* Iterate over the interface families and find one which is
-     available.  */
-  for (cnt = 0; cnt < nafs; ++cnt)
-    {
-      int type = SOCK_DGRAM;
-
-      if (has_proc && afs[cnt].procname[0] != '\0')
-	{
-	  strcpy (fname + 6, afs[cnt].procname);
-	  if (__access (fname, R_OK) == -1)
-	    /* The /proc entry is not available.  I.e., we cannot
-	       create a socket of this type (without loading the
-	       module).  Don't look for it since this might trigger
-	       loading the module.  */
-	    continue;
-	}
-
-      if (afs[cnt].family == AF_NETROM || afs[cnt].family == AF_X25)
-	type = SOCK_SEQPACKET;
-
-      result = __socket (afs[cnt].family, type | SOCK_CLOEXEC, 0);
-      if (result != -1)
-	{
-	  /* Found an available family.  */
-	  last_type = type;
-	  last_family = afs[cnt].family;
-	  return result;
-	}
-    }
-
-  /* None of the protocol families is available.  It is unclear what kind
-     of error is returned.  ENOENT seems like a reasonable choice.  */
-  __set_errno (ENOENT);
-  return -1;
+  /* Netlink support is always part of the kernel, so we just use a
+     netlink socket.  */
+  return __socket (PF_NETLINK, SOCK_DGRAM | SOCK_CLOEXEC, NETLINK_ROUTE);
 }
diff --git a/sysdeps/unix/sysv/linux/s390/opensock.c b/sysdeps/unix/sysv/linux/s390/opensock.c
deleted file mode 100644
index f099d651ff..0000000000
--- a/sysdeps/unix/sysv/linux/s390/opensock.c
+++ /dev/null
@@ -1,2 +0,0 @@
-#define NEED_AF_IUCV 1
-#include "../opensock.c"