[PATCH v2] libtracefs: Add new API for open trace marker file

[PATCH v2] libtracefs: Add new API for open trace marker file

[Tzvetomir Stoyanov (VMware)]

Added new APIs for opening trace_marker file of given instance:
   tracefs_marker_init()
   tracefs_marker_write()
   tracefs_marker_vprint()
   tracefs_marker_print()
   tracefs_marker_close()

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
Apply on top of "libtracefs: Update filtering functions"
https://lore.kernel.org/linux-trace-devel/20210407202126.1870994-1-rostedt@goodmis.org/

v2 changes:
 - Added set of new APIs, instead of the previously proposed API for just
   opening the file.

 include/tracefs-local.h |   1 +
 include/tracefs.h       |   9 +++
 src/Makefile            |   1 +
 src/tracefs-instance.c  |   3 +
 src/tracefs-marker.c    | 129 ++++++++++++++++++++++++++++++++++++++++
 5 files changed, 143 insertions(+)
 create mode 100644 src/tracefs-marker.c

diff --git a/include/tracefs-local.h b/include/tracefs-local.h
index 6865611..6657b6f 100644
--- a/include/tracefs-local.h
+++ b/include/tracefs-local.h
@@ -21,6 +21,7 @@ struct tracefs_instance {
 	int			flags;
 	int			ftrace_filter_fd;
 	int			ftrace_notrace_fd;
+	int			ftrace_marker_fd;
 };
 
 extern pthread_mutex_t toplevel_lock;
diff --git a/include/tracefs.h b/include/tracefs.h
index 70b7ebe..9adcf07 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -63,6 +63,15 @@ static inline int tracefs_trace_on_get_fd(struct tracefs_instance *instance)
 	return tracefs_instance_file_open(instance, "tracing_on", O_RDWR);
 }
 
+/* trace marker */
+int tracefs_marker_init(struct tracefs_instance *instance);
+int tracefs_marker_print(struct tracefs_instance *instance,
+			 const char *fmt, ...);
+int tracefs_marker_vprint(struct tracefs_instance *instance,
+			   const char *fmt, va_list ap);
+int tracefs_marker_write(struct tracefs_instance *instance, void *data, int len);
+void tracefs_marker_close(struct tracefs_instance *instance);
+
 /* events */
 void tracefs_list_free(char **list);
 char **tracefs_event_systems(const char *tracing_dir);
diff --git a/src/Makefile b/src/Makefile
index dabdbb4..b4cff07 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -7,6 +7,7 @@ OBJS += tracefs-utils.o
 OBJS += tracefs-instance.o
 OBJS += tracefs-events.o
 OBJS += tracefs-tools.o
+OBJS += tracefs-marker.o
 
 OBJS := $(OBJS:%.o=$(bdir)/%.o)
 DEPS := $(OBJS:$(bdir)/%.o=$(bdir)/.%.d)
diff --git a/src/tracefs-instance.c b/src/tracefs-instance.c
index 599c3a7..90e35b4 100644
--- a/src/tracefs-instance.c
+++ b/src/tracefs-instance.c
@@ -49,6 +49,7 @@ static struct tracefs_instance *instance_alloc(const char *trace_dir, const char
 
 	instance->ftrace_filter_fd = -1;
 	instance->ftrace_notrace_fd = -1;
+	instance->ftrace_marker_fd = -1;
 
 	return instance;
 
@@ -74,6 +75,8 @@ void tracefs_instance_free(struct tracefs_instance *instance)
 	free(instance->trace_dir);
 	free(instance->name);
 	pthread_mutex_destroy(&instance->lock);
+	if (instance->ftrace_marker_fd >= 0)
+		close(instance->ftrace_marker_fd);
 	free(instance);
 }
 
diff --git a/src/tracefs-marker.c b/src/tracefs-marker.c
new file mode 100644
index 0000000..92d55f8
--- /dev/null
+++ b/src/tracefs-marker.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: LGPL-2.1
+/*
+ * Copyright (C) 2021, VMware, Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
+ *
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+
+#include "tracefs.h"
+#include "tracefs-local.h"
+
+/* File descriptor for Top level trace_marker */
+static int ftrace_marker_fd = -1;
+
+/**
+ * tracefs_marker_init - Open trace_marker file of selected instance for writing
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ *
+ * Returns 0 if the trace_marker is opened successfully, or -1 in case of an error
+ */
+int tracefs_marker_init(struct tracefs_instance *instance)
+{
+	int *fd = instance ? &instance->ftrace_marker_fd : &ftrace_marker_fd;
+
+	if (*fd >= 0)
+		return 0;
+	*fd = tracefs_instance_file_open(instance, "trace_marker", O_WRONLY);
+
+	return *fd < 0 ? -1 : 0;
+}
+
+/**
+ * tracefs_marker_write - Write binary data in the trace marker
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ * @data: binary data, that is going to be written in the trace marker
+ * @len: length of the @data
+ *
+ * If the trace marker file of the desired instance is not open already,
+ * this API will open it for writing. The file will stay open until
+ * tracefs_marker_close() is called.
+ *
+ * Returns 0 if the data is written correctly, or -1 in case of an error
+ */
+int tracefs_marker_write(struct tracefs_instance *instance, void *data, int len)
+{
+	int *fd = instance ? &instance->ftrace_marker_fd : &ftrace_marker_fd;
+	int ret;
+
+	if (!data || len < 1)
+		return -1;
+	if (*fd < 0) {
+		ret = tracefs_marker_init(instance);
+		if (ret < 0)
+			return ret;
+	}
+
+	ret = write(*fd, data, len);
+
+	return ret == len ? 0 : -1;
+}
+
+/**
+ * tracefs_marker_vprint - Write a formatted string in the trace marker
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ * @fmt: pritnf formatted string
+ * @ap: list of arguments for the formatted string
+ *
+ * If the trace marker file of the desired instance is not open already,
+ * this API will open it for writing. The file will stay open until
+ * tracefs_marker_close() is called.
+ *
+ * Returns 0 if the string is written correctly, or -1 in case of an error
+ */
+int tracefs_marker_vprint(struct tracefs_instance *instance,
+			   const char *fmt, va_list ap)
+{
+	char *str = NULL;
+	int ret;
+
+	ret = vasprintf(&str, fmt, ap);
+	if (ret < 0)
+		return ret;
+	ret = tracefs_marker_write(instance, str, strlen(str) + 1);
+	free(str);
+
+	return ret;
+}
+
+/**
+ * tracefs_marker_print - Write a formatted string in the trace marker
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ * @fmt: pritnf formatted string with variable arguments ...
+ *
+ * If the trace marker file of the desired instance is not open already,
+ * this API will open it for writing. The file will stay open until
+ * tracefs_marker_close() is called.
+ *
+ * Returns 0 if the string is written correctly, or -1 in case of an error
+ */
+int tracefs_marker_print(struct tracefs_instance *instance,
+			 const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	va_start(ap, fmt);
+	ret = tracefs_marker_vprint(instance, fmt, ap);
+	va_end(ap);
+
+	return ret;
+}
+
+/**
+ * tracefs_marker_close - Close trace_marker file of selected instance
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ *
+ * Closes the file, previously opened with any of the other tracefs_marker_ APIs
+ */
+void tracefs_marker_close(struct tracefs_instance *instance)
+{
+	int *fd = instance ? &instance->ftrace_marker_fd : &ftrace_marker_fd;
+
+	if (*fd < 0)
+		return;
+	close(*fd);
+	*fd = -1;
+}
-- 
2.30.2

Re: [PATCH v2] libtracefs: Add new API for open trace marker file

[Steven Rostedt]

On Thu,  8 Apr 2021 11:08:21 +0300
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:

> Added new APIs for opening trace_marker file of given instance:
>    tracefs_marker_init()
>    tracefs_marker_write()
>    tracefs_marker_vprint()
>    tracefs_marker_print()
>    tracefs_marker_close()

I really don't like the name as it's more about the tracefs implementation
and not what it's used for. I much rather have:

	tracefs_print_init();
	tracefs_printf();
	tracefs_vprintf();
	tracefs_print_close();

And you should never write binary into the trace_marker file, as it always
expects ascii strings. That's the trace_marker_raw file. In which case we
could have:

	tracefs_binary_init();
	tracefs_binary_write();
	tracefs_binary_close();

For binary writes.

-- Steve

Re: [PATCH v2] libtracefs: Add new API for open trace marker file

[Tzvetomir Stoyanov]

On Thu, Apr 8, 2021 at 3:59 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Thu,  8 Apr 2021 11:08:21 +0300
> "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:
>
> > Added new APIs for opening trace_marker file of given instance:
> >    tracefs_marker_init()
> >    tracefs_marker_write()
> >    tracefs_marker_vprint()
> >    tracefs_marker_print()
> >    tracefs_marker_close()
>
> I really don't like the name as it's more about the tracefs implementation
> and not what it's used for. I much rather have:
>
>         tracefs_print_init();
>         tracefs_printf();
>         tracefs_vprintf();
>         tracefs_print_close();
>
> And you should never write binary into the trace_marker file, as it always
> expects ascii strings. That's the trace_marker_raw file. In which case we
> could have:
>
>         tracefs_binary_init();
>         tracefs_binary_write();
>         tracefs_binary_close();
>
> For binary writes.
>
I find "tracefs_print_" a little bit confusing, like printing
something on console. I think the name should stress that a user
string/data is written in the trace buffer. I would like to combine
string and binary APIs into one set, something like:

 tracefs_user_trace_init();  /* open both trace_marker and
trace_marker_raw files, or have flags to specify what file to open,
string or data*/
 tracefs_user_trace_printf(); /* write to  trace_marker */
 tracefs_user_trace_vprintf(); /* write to  trace_marker */
 tracefs_user_trace_binary(); /* write to  trace_marker_raw */
 tracefs_user_trace_init(); /* close both string and data fd, if open */


> -- Steve



-- 
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center

Re: [PATCH v2] libtracefs: Add new API for open trace marker file

[Steven Rostedt]

On Thu, 8 Apr 2021 16:21:52 +0300
Tzvetomir Stoyanov <tz.stoyanov@gmail.com> wrote:


> I find "tracefs_print_" a little bit confusing, like printing
> something on console. I think the name should stress that a user
> string/data is written in the trace buffer. I would like to combine
> string and binary APIs into one set, something like:

How so? We use it in the kernel "trace_printk()" there's no confusion there.

And to me, "user string written in the trace buffer" is exactly what
I think when I see "tracefs_printf()".

> 
>  tracefs_user_trace_init();  /* open both trace_marker and
> trace_marker_raw files, or have flags to specify what file to open,
> string or data*/
>  tracefs_user_trace_printf(); /* write to  trace_marker */
>  tracefs_user_trace_vprintf(); /* write to  trace_marker */
>  tracefs_user_trace_binary(); /* write to  trace_marker_raw */
>  tracefs_user_trace_init(); /* close both string and data fd, if open */
> 

I have no idea what "user_trace" is. What does that mean? There's no
precedence for it.

"tracefs_printf()" is short and to the point, and states exactly what you
want. It does a printf() into the tracefs system. How is that confusing?

We have fprintf() which does a printf into a file point.
We have sprintf() which does an printf into a string.

Thus, it makes sense to have "tracefs_printf()" which does a printf into
the tracefs file system. Just like we have trace_seq_printf() which does a
printf() into the trace_seq.

"printf()" means string manipulation, and has nothing to do with consoles.

I personally hate long function names, especially ones that I may use
a lot of.

Keeping with the other APIs trace_printf() is the only one that seems
reasonable.

-- Steve