Subject: [PATCH net-next v2 1/6] selftests: net: py: teach ksft_pr() multi-line safety

From: Jakub Kicinski <[email-masked]>
Date: Fri, 9 Jan 2026 16:51:16 -0800

Make printing multi-line logs easier by automatically prefixing
each line in ksft_pr(). Make use of this when formatting exceptions.

Signed-off-by: Jakub Kicinski <[email-masked]>
---
 tools/testing/selftests/net/lib/py/ksft.py | 29 ++++++++++++++--------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/tools/testing/selftests/net/lib/py/ksft.py b/tools/testing/selftests/net/lib/py/ksft.py
index 531e7fa1b3ea..4ca21d829b1c 100644
--- a/tools/testing/selftests/net/lib/py/ksft.py
+++ b/tools/testing/selftests/net/lib/py/ksft.py
@@ -32,8 +32,23 @@ KSFT_DISRUPTIVE = True

 def ksft_pr(*objs, **kwargs):
+    """
+    Print logs to stdout.
+
+    Behaves like print() but log lines will be prefixed
+    with # to prevent breaking the TAP output formatting.
+
+    Extra arguments (on top of what print() supports):
+      line_pfx - add extra string before each line
+    """
+    sep = kwargs.pop("sep", " ")
+    pfx = kwargs.pop("line_pfx", "")
+    pfx = "#" + (" " + pfx if pfx else "")
     kwargs["flush"] = True
-    print("#", *objs, **kwargs)
+
+    text = sep.join(str(obj) for obj in objs)
+    prefixed = f"\n{pfx} ".join(text.split('\n'))
+    print(pfx, prefixed, **kwargs)

 def _fail(*args):
@@ -165,9 +180,7 @@ KSFT_DISRUPTIVE = True
             entry.exec_only()
         except Exception:
             ksft_pr(f"Exception while handling defer / cleanup (callback {i} of {qlen_start})!")
-            tb = traceback.format_exc()
-            for line in tb.strip().split('\n'):
-                ksft_pr("Defer Exception|", line)
+            ksft_pr(traceback.format_exc(), line_pfx="Defer Exception|")
             KSFT_RESULT = False

@@ -325,9 +338,7 @@ KsftCaseFunction = namedtuple("KsftCaseFunction",
             cnt_key = 'xfail'
         except BaseException as e:
             stop |= isinstance(e, KeyboardInterrupt)
-            tb = traceback.format_exc()
-            for line in tb.strip().split('\n'):
-                ksft_pr("Exception|", line)
+            ksft_pr(traceback.format_exc(), line_pfx="Exception|")
             if stop:
                 ksft_pr(f"Stopping tests due to {type(e).__name__}.")
             KSFT_RESULT = False
@@ -336,9 +347,7 @@ KsftCaseFunction = namedtuple("KsftCaseFunction",
         try:
             ksft_flush_defer()
         except BaseException as e:
-            tb = traceback.format_exc()
-            for line in tb.strip().split('\n'):
-                ksft_pr("Exception|", line)
+            ksft_pr(traceback.format_exc(), line_pfx="Exception|")
             if isinstance(e, KeyboardInterrupt):
                 ksft_pr()
                 ksft_pr("WARN: defer() interrupted, cleanup may be incomplete.")
-- 
2.52.0