Re: [PATCH net-next] selftests: net: add ctl_file_write() helper

Setting a sysctl or a sysfs attribute for the duration of a test and
putting the old value back has been open coded multiple times.

We generally avoid creating library helpers but this one is very
common, and the defer is a little tricky as using the same function
for defer as the initial write leads to an infinite loop (not that
I would ever make such mistake!)

Some of the conversions are not identical, but arguably ctl_file_write()
semantics are more correct.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: shuah@kernel.org
CC: cjubran@nvidia.com
CC: cratiu@nvidia.com
CC: noren@nvidia.com
CC: willemb@google.com
CC: petrm@nvidia.com
CC: linux-kselftest@vger.kernel.org
---
 tools/testing/selftests/drivers/net/gro.py    | 17 +++---------
 .../drivers/net/hw/devlink_rate_tc_bw.py      |  5 ++--
 tools/testing/selftests/drivers/net/hw/irq.py | 11 ++------
 .../drivers/net/hw/lib/py/__init__.py         |  4 +--
 .../selftests/drivers/net/hw/toeplitz.py      | 10 +++----
 .../selftests/drivers/net/lib/py/__init__.py  |  4 +--
 .../selftests/drivers/net/ring_reconfig.py    | 26 ++++---------------
 .../testing/selftests/net/lib/py/__init__.py  |  4 +--
 tools/testing/selftests/net/lib/py/utils.py   | 22 ++++++++++++++++
 9 files changed, 44 insertions(+), 59 deletions(-)

diff --git a/tools/testing/selftests/drivers/net/gro.py b/tools/testing/selftests/drivers/net/gro.py
index 6ab8c97880d1..e0b21703cc3c 100755
--- a/tools/testing/selftests/drivers/net/gro.py
+++ b/tools/testing/selftests/drivers/net/gro.py

@@ -42,7 +42,7 @@ import re
 from lib.py import ksft_run, ksft_exit, ksft_pr
 from lib.py import NetDrvEpEnv, KsftFailEx, KsftXfailEx
 from lib.py import NetdevFamily, EthtoolFamily
-from lib.py import bkg, cmd, defer, ethtool, ip
+from lib.py import bkg, cmd, ctl_file_write, defer, ethtool, ip
 from lib.py import ksft_variants, KsftNamedVariant
 
 

@@ -79,17 +79,6 @@ GRO_DPORT = 8000
     return getattr(cfg, attr)
 
 
-def _write_defer_restore(cfg, path, val, defer_undo=False):
-    with open(path, "r", encoding="utf-8") as fp:
-        orig_val = fp.read().strip()
-        if str(val) == orig_val:
-            return
-    with open(path, "w", encoding="utf-8") as fp:
-        fp.write(val)
-    if defer_undo:
-        defer(_write_defer_restore, cfg, path, orig_val)
-
-
 def _set_mtu_restore(dev, mtu, host):
     if dev['mtu'] < mtu:
         ip(f"link set dev {dev['ifname']} mtu {mtu}", host=host)

@@ -244,8 +233,8 @@ def _run_gro_bin(cfg, test_name, protocol=None, num_flows=None,
         flush_path = f"/sys/class/net/{cfg.ifname}/gro_flush_timeout"
         irq_path = f"/sys/class/net/{cfg.ifname}/napi_defer_hard_irqs"
 
-        _write_defer_restore(cfg, flush_path, "200000", defer_undo=True)
-        _write_defer_restore(cfg, irq_path, "10", defer_undo=True)
+        ctl_file_write(flush_path, "200000")
+        ctl_file_write(irq_path, "10")
 
         _set_ethtool_feat(cfg.ifname, cfg.feat,
                           {"generic-receive-offload": True,

diff --git a/tools/testing/selftests/drivers/net/hw/devlink_rate_tc_bw.py b/tools/testing/selftests/drivers/net/hw/devlink_rate_tc_bw.py
index 4e4faa9275bb..38d712755257 100755
--- a/tools/testing/selftests/drivers/net/hw/devlink_rate_tc_bw.py
+++ b/tools/testing/selftests/drivers/net/hw/devlink_rate_tc_bw.py

@@ -63,7 +63,7 @@ from lib.py import ksft_pr, ksft_run, ksft_exit
 from lib.py import KsftSkipEx, KsftFailEx, KsftXfailEx
 from lib.py import NetDrvEpEnv, DevlinkFamily
 from lib.py import NlError
-from lib.py import cmd, defer, ethtool, ip
+from lib.py import cmd, ctl_file_write, defer, ethtool, ip
 from lib.py import Iperf3Runner
 
 

@@ -113,8 +113,7 @@ from lib.py import Iperf3Runner
     except Exception as exc:
         raise KsftSkipEx(f"Failed to enable switchdev mode on {cfg.pci}") from exc
     try:
-        cmd(f"echo 1 > /sys/class/net/{cfg.ifname}/device/sriov_numvfs", shell=True)
-        defer(cmd, f"echo 0 > /sys/class/net/{cfg.ifname}/device/sriov_numvfs", shell=True)
+        ctl_file_write(f"/sys/class/net/{cfg.ifname}/device/sriov_numvfs", 1)
     except Exception as exc:
         raise KsftSkipEx(f"Failed to enable SR-IOV on {cfg.ifname}") from exc
 

diff --git a/tools/testing/selftests/drivers/net/hw/irq.py b/tools/testing/selftests/drivers/net/hw/irq.py
index 0699d6a8b4e2..3d1c56b51054 100755
--- a/tools/testing/selftests/drivers/net/hw/irq.py
+++ b/tools/testing/selftests/drivers/net/hw/irq.py

@@ -7,7 +7,7 @@ from lib.py import KsftSkipEx
 from lib.py import ksft_disruptive
 from lib.py import EthtoolFamily, NetdevFamily
 from lib.py import NetDrvEnv
-from lib.py import cmd, ip, defer
+from lib.py import cmd, ctl_file_write, ip
 
 
 def read_affinity(irq) -> str:

@@ -15,12 +15,6 @@ from lib.py import cmd, ip, defer
         return fp.read().lstrip("0,").strip()
 
 
-def write_affinity(irq, what) -> str:
-    if what != read_affinity(irq):
-        with open(f'/proc/irq/{irq}/smp_affinity', 'w') as fp:
-            fp.write(what)
-
-
 def check_irqs_reported(cfg) -> None:
     """ Check that device reports IRQs for NAPI instances """
     napis = cfg.netnl.napi_get({"ifindex": cfg.ifindex}, dump=True)

@@ -41,8 +35,7 @@ from lib.py import cmd, ip, defer
     old = read_affinity(n['irq'])
     # pick an affinity that's not the current one
     new = "3" if old != "3" else "5"
-    write_affinity(n['irq'], new)
-    defer(write_affinity, n['irq'], old)
+    ctl_file_write(f"/proc/irq/{n['irq']}/smp_affinity", new)