Re: [PATCH v2 5/6] tools/virtio: use canonical ftrace path

From: Mukesh Ojha
Date: Fri Feb 17 2023 - 10:46:25 EST




On 2/16/2023 4:03 AM, Ross Zwisler wrote:
The canonical location for the tracefs filesystem is at /sys/kernel/tracing.

But, from Documentation/trace/ftrace.rst:

Before 4.1, all ftrace tracing control files were within the debugfs
file system, which is typically located at /sys/kernel/debug/tracing.
For backward compatibility, when mounting the debugfs file system,
the tracefs file system will be automatically mounted at:

/sys/kernel/debug/tracing

A few spots in tools/virtio still refer to this older debugfs
path, so let's update them to avoid confusion.

Signed-off-by: Ross Zwisler <zwisler@xxxxxxxxxx>
---
tools/virtio/virtio-trace/README | 2 +-
tools/virtio/virtio-trace/trace-agent.c | 12 ++++++++----
2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/tools/virtio/virtio-trace/README b/tools/virtio/virtio-trace/README
index b64845b823ab..cea29a2a4c0a 100644
--- a/tools/virtio/virtio-trace/README
+++ b/tools/virtio/virtio-trace/README
@@ -95,7 +95,7 @@ Run
1) Enable ftrace in the guest
<Example>
- # echo 1 > /sys/kernel/debug/tracing/events/sched/enable
+ # echo 1 > /sys/kernel/tracing/events/sched/enable
2) Run trace agent in the guest
This agent must be operated as root.
diff --git a/tools/virtio/virtio-trace/trace-agent.c b/tools/virtio/virtio-trace/trace-agent.c
index cdfe77c2b4c8..7e2d9bbf0b84 100644
--- a/tools/virtio/virtio-trace/trace-agent.c
+++ b/tools/virtio/virtio-trace/trace-agent.c
@@ -18,8 +18,9 @@
#define PIPE_DEF_BUFS 16
#define PIPE_MIN_SIZE (PAGE_SIZE*PIPE_DEF_BUFS)
#define PIPE_MAX_SIZE (1024*1024)
-#define READ_PATH_FMT \
- "/sys/kernel/debug/tracing/per_cpu/cpu%d/trace_pipe_raw"
+#define TRACEFS "/sys/kernel/tracing"
+#define DEBUGFS "/sys/kernel/debug/tracing"
+#define READ_PATH_FMT "%s/per_cpu/cpu%d/trace_pipe_raw"
#define WRITE_PATH_FMT "/dev/virtio-ports/trace-path-cpu%d"
#define CTL_PATH "/dev/virtio-ports/agent-ctl-path"
@@ -120,9 +121,12 @@ static const char *make_path(int cpu_num, bool this_is_write_path)
if (this_is_write_path)
/* write(output) path */
ret = snprintf(buf, PATH_MAX, WRITE_PATH_FMT, cpu_num);
- else
+ else {
/* read(input) path */
- ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, cpu_num);
+ ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, TRACEFS, cpu_num);
+ if (ret > 0 && access(buf, F_OK) != 0)
+ ret = snprintf(buf, PATH_MAX, READ_PATH_FMT, DEBUGFS, cpu_num);
+ }



Reviewed-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>

-Mukesh


if (ret <= 0) {
pr_err("Failed to generate %s path(CPU#%d):%d\n",