selftests: bpf: log direct file writes

Recent changes to netdevsim moved creating and destroying
devices from netlink to sysfs. The sysfs writes have been
implemented as direct writes, without shelling out. This
is faster, but leaves no trace in the logs. Add explicit
logs to make debugging possible.
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Acked-by: NDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

tools/testing/selftests/bpf/test_offload.py

@@ -335,13 +335,22 @@ class NetdevSimDev:
     """
     Class for netdevsim bus device and its attributes.
     """
+    @staticmethod
+    def ctrl_write(path, val):
+        fullpath = os.path.join("/sys/bus/netdevsim/", path)
+        try:
+            with open(fullpath, "w") as f:
+                f.write(val)
+        except OSError as e:
+            log("WRITE %s: %r" % (fullpath, val), -e.errno)
+            raise e
+        log("WRITE %s: %r" % (fullpath, val), 0)
 
     def __init__(self, port_count=1):
         addr = 0
         while True:
             try:
-                with open("/sys/bus/netdevsim/new_device", "w") as f:
-                    f.write("%u %u" % (addr, port_count))
+                self.ctrl_write("new_device", "%u %u" % (addr, port_count))
             except OSError as e:
                 if e.errno == errno.ENOSPC:
                     addr += 1
@@ -403,14 +412,13 @@ class NetdevSimDev:
         return progs
 
     def remove(self):
-        with open("/sys/bus/netdevsim/del_device", "w") as f:
-            f.write("%u" % self.addr)
+        self.ctrl_write("del_device", "%u" % (self.addr, ))
         devs.remove(self)
 
     def remove_nsim(self, nsim):
         self.nsims.remove(nsim)
-        with open("/sys/bus/netdevsim/devices/netdevsim%u/del_port" % self.addr ,"w") as f:
-            f.write("%u" % nsim.port_index)
+        self.ctrl_write("devices/netdevsim%u/del_port" % (self.addr, ),
+                        "%u" % (nsim.port_index, ))
 
 class NetdevSim:
     """