selftests: drv-net: wait for carrier

On fast machines the tests run in quick succession so even
when tests clean up after themselves the carrier may need
some time to come back.

Specifically in NIPA when ping.py runs right after netpoll_basic.py
the first ping command fails.

Since the context manager callbacks are now common NetDrvEpEnv
gets an ip link up call as well.

Reviewed-by: Joe Damato <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/testing/selftests/drivers/net/lib/py/__init__.py

···
         NlError, RtnlFamily, DevlinkFamily
     from net.lib.py import CmdExitFailure
     from net.lib.py import bkg, cmd, bpftool, bpftrace, defer, ethtool, \
-        fd_read_timeout, ip, rand_port, tool, wait_port_listen
+        fd_read_timeout, ip, rand_port, tool, wait_port_listen, wait_file
     from net.lib.py import fd_read_timeout
     from net.lib.py import KsftSkipEx, KsftFailEx, KsftXfailEx
     from net.lib.py import ksft_disruptive, ksft_exit, ksft_pr, ksft_run, \

tools/testing/selftests/drivers/net/lib/py/env.py

···
 import time
 from pathlib import Path
 from lib.py import KsftSkipEx, KsftXfailEx
-from lib.py import ksft_setup
+from lib.py import ksft_setup, wait_file
 from lib.py import cmd, ethtool, ip, CmdExitFailure
 from lib.py import NetNS, NetdevSimDev
 from .remote import Remote
···
         self.net_lib_dir = (Path(__file__).parent / "../../../../net/lib").resolve()
 
         self.env = self._load_env_file()
+
+        # Following attrs must be set be inheriting classes
+        self.dev = None
 
     def _load_env_file(self):
         env = os.environ.copy()
···
                 env[pair[0]] = pair[1]
         return ksft_setup(env)
 
+    def __del__(self):
+        pass
+
+    def __enter__(self):
+        ip(f"link set dev {self.dev['ifname']} up")
+        wait_file(f"/sys/class/net/{self.dev['ifname']}/carrier",
+                  lambda x: x.strip() == "1")
+
+        return self
+
+    def __exit__(self, ex_type, ex_value, ex_tb):
+        """
+        __exit__ gets called at the end of a "with" block.
+        """
+        self.__del__()
+
 
 class NetDrvEnv(NetDrvEnvBase):
     """
···
             self.dev = self._ns.nsims[0].dev
         self.ifname = self.dev['ifname']
         self.ifindex = self.dev['ifindex']
-
-    def __enter__(self):
-        ip(f"link set dev {self.dev['ifname']} up")
-
-        return self
-
-    def __exit__(self, ex_type, ex_value, ex_tb):
-        """
-        __exit__ gets called at the end of a "with" block.
-        """
-        self.__del__()
 
     def __del__(self):
         if self._ns:
···
         if (v4 and len(v4) > 1) or (v6 and len(v6) > 1):
             raise Exception("Can't resolve remote interface name, multiple interfaces match")
         return v6[0]["ifname"] if v6 else v4[0]["ifname"]
-
-    def __enter__(self):
-        return self
-
-    def __exit__(self, ex_type, ex_value, ex_tb):
-        """
-        __exit__ gets called at the end of a "with" block.
-        """
-        self.__del__()
 
     def __del__(self):
         if self._ns:

tools/testing/selftests/net/lib/py/utils.py

···
         if time.monotonic() > end:
             raise Exception("Waiting for port listen timed out")
         time.sleep(sleep)
+
+
+def wait_file(fname, test_fn, sleep=0.005, deadline=5, encoding='utf-8'):
+    """
+    Wait for file contents on the local system to satisfy a condition.
+    test_fn() should take one argument (file contents) and return whether
+    condition is met.
+    """
+    end = time.monotonic() + deadline
+
+    with open(fname, "r", encoding=encoding) as fp:
+        while True:
+            if test_fn(fp.read()):
+                break
+            fp.seek(0)
+            if time.monotonic() > end:
+                raise TimeoutError("Wait for file contents failed", fname)
+            time.sleep(sleep)