On ARM64 kernels with 64K pages, the trace_marker_raw test fails because
bash's printf builtin uses stdio buffering which splits output into
multiple small write() calls to the tracefs file. Since each individual
write is within TRACE_MARKER_MAX_SIZE (4096), they all succeed, causing
the "too big" write test to incorrectly pass.
Fix by writing through dd with iflag=fullblock to guarantee a single
atomic write() syscall to trace_marker_raw.
Fixes: 37f46601383a ("selftests/tracing: Add basic test for trace_marker_raw
file")
Signed-off-by: Tianchen Ding <[email protected]>
---
v3:
Measure the binary length via wc -c instead of hard-coding "size + 4".
v2:
Update comment about 64K pages.
---
.../ftrace/test.d/00basic/trace_marker_raw.tc | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
index 8e905d4fe6dd..f985ff391463 100644
--- a/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
+++ b/tools/testing/selftests/ftrace/test.d/00basic/trace_marker_raw.tc
@@ -36,15 +36,23 @@ make_str() {
data=`printf -- 'X%.0s' $(seq $cnt)`
- printf "${val}${data}"
+ # Return escape-sequence text (e.g. "\003\000..."); the caller
+ # converts to binary. Shell command substitution strips NUL bytes,
+ # so the binary form cannot survive being captured into a variable.
+ printf '%s' "${val}${data}"
}
write_buffer() {
id=$1
size=$2
- # write the string into the raw marker
- make_str $id $size > trace_marker_raw
+ str=`make_str $id $size`
+ len=`printf "$str" | wc -c`
+ # Pipe through dd to ensure a single atomic write() syscall
+ # on architectures with 64K pages, where shell's printf builtin
+ # uses stdio buffering which may split the output into multiple
+ # writes.
+ printf "$str" | dd of=trace_marker_raw bs=$len iflag=fullblock
}
--
2.39.3
