netdev-linux: Avoid RTM_GETQDISC bug workaround on new-enough kernels.

Otherwise we can't detect classless qdiscs.

This has no useful effect for the currently supported qdiscs, which all
have classes, but it makes it possible to add support for new classless
qdiscs.

This suddenly makes netdev-linux complain about qdiscs it doesn't know
about (e.g. pfifo_fast), which isn't too useful, so this commit also
demotes that INFO message to DBG level.

Reported-by: Jonathan Vestin <jonavest@kau.se>
Signed-off-by: Ben Pfaff <blp@nicira.com>

diff --git a/AUTHORS b/AUTHORS
index 008f6f1..db4520f 100644 (file)
--- a/AUTHORS
+++ b/AUTHORS
@@ -268,6 +268,7 @@ Joan Cirer              joan@ev0.net
 John Darrington         john@darrington.wattle.id.au
 John Galgay             john@galgay.net
 John Hurley             john.hurley@netronome.com
+Jonathan Vestin         jonavest@kau.se
 K 華                    k940545@hotmail.com
 Kevin Mancuso           kevin.mancuso@rackspace.com
 Kiran Shanbhog          kiran@vmware.com

diff --git a/lib/netdev-linux.c b/lib/netdev-linux.c
index 6e574cd..9b2e74f 100644 (file)
--- a/lib/netdev-linux.c
+++ b/lib/netdev-linux.c
@@ -36,6 +36,7 @@
 #include <sys/types.h>
 #include <sys/ioctl.h>
 #include <sys/socket.h>
+#include <sys/utsname.h>
 #include <netpacket/packet.h>
 #include <net/if.h>
 #include <net/if_arp.h>
@@ -4405,6 +4406,31 @@ tc_del_qdisc(struct netdev *netdev_)
     return error;
 }
 
+static bool
+getqdisc_is_safe(void)
+{
+    static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER;
+    static bool safe = false;
+
+    if (ovsthread_once_start(&once)) {
+        struct utsname utsname;
+        int major, minor;
+
+        if (uname(&utsname) == -1) {
+            VLOG_WARN("uname failed (%s)", ovs_strerror(errno));
+        } else if (!ovs_scan(utsname.release, "%d.%d", &major, &minor)) {
+            VLOG_WARN("uname reported bad OS release (%s)", utsname.release);
+        } else if (major < 2 || (major == 2 && minor < 35)) {
+            VLOG_INFO("disabling unsafe RTM_GETQDISC in Linux kernel %s",
+                      utsname.release);
+        } else {
+            safe = true;
+        }
+        ovsthread_once_done(&once);
+    }
+    return safe;
+}
+
 /* If 'netdev''s qdisc type and parameters are not yet known, queries the
  * kernel to determine what they are.  Returns 0 if successful, otherwise a
  * positive errno value. */
@@ -4434,18 +4460,21 @@ tc_query_qdisc(const struct netdev *netdev_)
      * create will have a class with handle 1:0.  The built-in qdiscs only have
      * a class with handle 0:0.
      *
-     * We could check for Linux 2.6.35+ and use a more straightforward method
-     * there. */
+     * On Linux 2.6.35+ we use the straightforward method because it allows us
+     * to handle non-builtin qdiscs without handle 1:0 (e.g. codel).  However,
+     * in such a case we get no response at all from the kernel (!) if a
+     * builtin qdisc is in use (which is later caught by "!error &&
+     * !qdisc->size"). */
     tcmsg = tc_make_request(netdev_, RTM_GETQDISC, NLM_F_ECHO, &request);
     if (!tcmsg) {
         return ENODEV;
     }
-    tcmsg->tcm_handle = tc_make_handle(1, 0);
-    tcmsg->tcm_parent = 0;
+    tcmsg->tcm_handle = tc_make_handle(getqdisc_is_safe() ? 0 : 1, 0);
+    tcmsg->tcm_parent = getqdisc_is_safe() ? TC_H_ROOT : 0;
 
     /* Figure out what tc class to instantiate. */
     error = tc_transact(&request, &qdisc);
-    if (!error) {
+    if (!error && qdisc->size) {
         const char *kind;
 
         error = tc_parse_qdisc(qdisc, &kind, NULL);
@@ -4455,15 +4484,15 @@ tc_query_qdisc(const struct netdev *netdev_)
             ops = tc_lookup_linux_name(kind);
             if (!ops) {
                 static struct vlog_rate_limit rl2 = VLOG_RATE_LIMIT_INIT(1, 1);
-                VLOG_INFO_RL(&rl2, "unknown qdisc \"%s\"", kind);
+                VLOG_DBG_RL(&rl2, "unknown qdisc \"%s\"", kind);
 
                 ops = &tc_ops_other;
             }
         }
-    } else if (error == ENOENT) {
-        /* Either it's a built-in qdisc, or it's a qdisc set up by some
-         * other entity that doesn't have a handle 1:0.  We will assume
-         * that it's the system default qdisc. */
+    } else if ((!error && !qdisc->size) || error == ENOENT) {
+        /* Either it's a built-in qdisc, or (on Linux pre-2.6.35) it's a qdisc
+         * set up by some other entity that doesn't have a handle 1:0.  We will
+         * assume that it's the system default qdisc. */
         ops = &tc_ops_default;
         error = 0;
     } else {