[PATCH v2] libtracefs: Add APIs for data streaming

[PATCH v2] libtracefs: Add APIs for data streaming

[Yordan Karadzhov (VMware)]

The new APIs can be used to dump the content of "trace_pipe" into a
file or directly to "stdout". The "splice" system call is used to
moves the data without copying. The new functionality is essentially
identical to what 'trace-cmd show -p' does.

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
---

Changes in v2:
  - The setting of the signal disposition is removed from the library
    and is now responsibility of the caller. This in fact gives more
    options for the user.
  - The example provided in the documentation is updated accordingly.

 Documentation/libtracefs-stream.txt | 106 ++++++++++++++++++++++++++++
 include/tracefs-local.h             |   1 +
 include/tracefs.h                   |   5 ++
 src/tracefs-tools.c                 |  98 +++++++++++++++++++++++++
 4 files changed, 210 insertions(+)
 create mode 100644 Documentation/libtracefs-stream.txt

diff --git a/Documentation/libtracefs-stream.txt b/Documentation/libtracefs-stream.txt
new file mode 100644
index 0000000..24c2e47
--- /dev/null
+++ b/Documentation/libtracefs-stream.txt
@@ -0,0 +1,106 @@
+libtracefs(3)
+=============
+
+NAME
+----
+tracefs_trace_pipe_stream, tracefs_trace_pipe_print -
+redirect the stream of trace data to an output or stdout.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <tracefs.h>*
+
+int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
+int tracefs_trace_pipe_print(struct tracefs_instance *instance);
+
+--
+
+DESCRIPTION
+-----------
+If NULL is passed as _instance_, the top trace instance is used.
+The user can interrupt the streaming of the data by pressing Ctrl-c.
+
+The _tracefs_trace_pipe_stream()_ function redirects the stream of trace data to an output
+file. The "splice" system call is used to moves the data without copying between kernel
+address space and user address space. The _fd_ is the file descriptor of the output file
+and _flags_ is a bit mask of flags to be passed to the "splice" system call.
+
+The _tracefs_trace_pipe_print()_ function is similar to _tracefs_trace_pipe_stream()_, but
+the stream of trace data is redirected to stdout.
+
+
+RETURN VALUE
+------------
+The _tracefs_trace_pipe_stream()_, and _tracefs_trace_pipe_print()_ functions return 0 if the operation is
+successful, or -1 in case of an error.
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <unistd.h>
+#include <signal.h>
+
+#include <tracefs.h>
+
+void stop(int sig)
+{
+	tracefs_trace_pipe_stop(NULL);
+}
+
+int main()
+{
+	mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
+	const char *filename = "trace.txt";
+	int fd = creat(filename, mode);
+	int ret;
+
+	signal(SIGINT, stop);
+	ret = tracefs_trace_pipe_stream(fd, NULL, 0);
+	close(fd);
+
+	return ret;
+}
+--
+FILES
+-----
+[verse]
+--
+*tracefs.h*
+	Header file to include in order to have access to the library APIs.
+*-ltracefs*
+	Linker switch to add when building a program that uses the library.
+--
+
+SEE ALSO
+--------
+_libtracefs(3)_,
+_libtraceevent(3)_,
+_trace-cmd(1)_,
+Documentation/trace/ftrace.rst from the Linux kernel tree
+
+AUTHOR
+------
+[verse]
+--
+*Steven Rostedt* <rostedt@goodmis.org>
+*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
+--
+REPORTING BUGS
+--------------
+Report bugs to  <linux-trace-devel@vger.kernel.org>
+
+LICENSE
+-------
+libtracefs is Free Software licensed under the GNU LGPL 2.1
+
+RESOURCES
+---------
+https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
+
+COPYING
+-------
+Copyright \(C) 2021 VMware, Inc. Free use of this software is granted under
+the terms of the GNU Public License (GPL).
diff --git a/include/tracefs-local.h b/include/tracefs-local.h
index 9e3aa18..833f136 100644
--- a/include/tracefs-local.h
+++ b/include/tracefs-local.h
@@ -30,6 +30,7 @@ struct tracefs_instance {
 	int				ftrace_notrace_fd;
 	int				ftrace_marker_fd;
 	int				ftrace_marker_raw_fd;
+	int				pipe_keep_going;
 };
 
 extern pthread_mutex_t toplevel_lock;
diff --git a/include/tracefs.h b/include/tracefs.h
index e29b550..3c6741b 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -184,4 +184,9 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
 /* Control library logs */
 void tracefs_set_loglevel(enum tep_loglevel level);
 
+int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
+int tracefs_trace_pipe_print(struct tracefs_instance *instance);
+void tracefs_trace_pipe_stop(struct tracefs_instance *instance);
+
+
 #endif /* _TRACE_FS_H */
diff --git a/src/tracefs-tools.c b/src/tracefs-tools.c
index 0cbb56d..0c0c44f 100644
--- a/src/tracefs-tools.c
+++ b/src/tracefs-tools.c
@@ -912,3 +912,101 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
 	tracefs_put_tracing_file(filter_path);
 	return ret;
 }
+
+static int top_pipe_keep_going;
+
+/**
+ * tracefs_trace_pipe_stream - redirect the stream of trace data to an output
+ * file. The "splice" system call is used to moves the data without copying
+ * between kernel address space and user address space. The user can interrupt
+ * the streaming of the data by pressing Ctrl-c.
+ * @fd: The file descriptor of the output file.
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ * @flags: flags to be passed to the "splice" system call.
+ *
+ * Returns -1 in case of an error or 0 otherwise.
+ */
+int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance,
+			      int flags)
+{
+	int *keep_going = instance ? &instance->pipe_keep_going :
+				     &top_pipe_keep_going;
+	const char *file = "trace_pipe";
+	int brass[2], in_fd, ret = -1;
+	off_t data_size;
+
+	in_fd = tracefs_instance_file_open(instance, file, O_RDONLY);
+	if (in_fd < 0) {
+		tracefs_warning("Failed to open 'trace_pipe'.");
+		return ret;
+	}
+
+	if(pipe(brass) < 0) {
+		tracefs_warning("Failed to open pipe.");
+		goto close_file;
+	}
+
+	data_size = fcntl(brass[0], F_GETPIPE_SZ);
+	if (data_size <= 0) {
+		tracefs_warning("Failed to open pipe (size=0).");
+		goto close_all;
+	}
+
+	*keep_going = true;
+	while (*keep_going) {
+		ret = splice(in_fd, NULL,
+			     brass[1], NULL,
+			     data_size, flags);
+		if (ret < 0)
+			break;
+
+		ret = splice(brass[0], NULL,
+			     fd, NULL,
+			     data_size, flags);
+		if (ret < 0)
+			break;
+	}
+
+	/*
+	 * Do not return error in the case when the "splice" system call
+	 * was interrupted by the user (pressing Ctrl-c).
+	 */
+	if (!keep_going)
+		ret = 0;
+
+ close_all:
+	close(brass[0]);
+	close(brass[1]);
+ close_file:
+	close(in_fd);
+
+	return ret;
+}
+
+/**
+ * tracefs_trace_pipe_print - redirect the stream of trace data to "stdout".
+ * The "splice" system call is used to moves the data without copying
+ * between kernel address space and user address space.
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ *
+ * Returns -1 in case of an error or 0 otherwise.
+ */
+
+int tracefs_trace_pipe_print(struct tracefs_instance *instance)
+{
+   return tracefs_trace_pipe_stream(STDOUT_FILENO,
+				    instance,
+				    SPLICE_F_MORE | SPLICE_F_MOVE);
+}
+
+/**
+ * tracefs_trace_pipe_stop - stop the streaming of trace data.
+ * @instance: ftrace instance, can be NULL for top tracing instance.
+ */
+void tracefs_trace_pipe_stop(struct tracefs_instance *instance)
+{
+	if (instance)
+		instance->pipe_keep_going = false;
+	else
+		top_pipe_keep_going = false;
+}
-- 
2.27.0

Re: [PATCH v2] libtracefs: Add APIs for data streaming

[Steven Rostedt]

On Wed, 23 Jun 2021 15:05:26 +0300
"Yordan Karadzhov (VMware)" <y.karadz@gmail.com> wrote:

> The new APIs can be used to dump the content of "trace_pipe" into a
> file or directly to "stdout". The "splice" system call is used to
> moves the data without copying. The new functionality is essentially
> identical to what 'trace-cmd show -p' does.
> 
> Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
> ---
> 
> Changes in v2:
>   - The setting of the signal disposition is removed from the library
>     and is now responsibility of the caller. This in fact gives more
>     options for the user.
>   - The example provided in the documentation is updated accordingly.
> 
>  Documentation/libtracefs-stream.txt | 106 ++++++++++++++++++++++++++++
>  include/tracefs-local.h             |   1 +
>  include/tracefs.h                   |   5 ++
>  src/tracefs-tools.c                 |  98 +++++++++++++++++++++++++
>  4 files changed, 210 insertions(+)
>  create mode 100644 Documentation/libtracefs-stream.txt
> 
> diff --git a/Documentation/libtracefs-stream.txt b/Documentation/libtracefs-stream.txt
> new file mode 100644
> index 0000000..24c2e47
> --- /dev/null
> +++ b/Documentation/libtracefs-stream.txt
> @@ -0,0 +1,106 @@
> +libtracefs(3)
> +=============
> +
> +NAME
> +----
> +tracefs_trace_pipe_stream, tracefs_trace_pipe_print -
> +redirect the stream of trace data to an output or stdout.
> +
> +SYNOPSIS
> +--------
> +[verse]
> +--
> +*#include <tracefs.h>*
> +
> +int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
> +int tracefs_trace_pipe_print(struct tracefs_instance *instance);
> +
> +--
> +
> +DESCRIPTION
> +-----------
> +If NULL is passed as _instance_, the top trace instance is used.
> +The user can interrupt the streaming of the data by pressing Ctrl-c.
> +
> +The _tracefs_trace_pipe_stream()_ function redirects the stream of trace data to an output
> +file. The "splice" system call is used to moves the data without copying between kernel
> +address space and user address space. The _fd_ is the file descriptor of the output file
> +and _flags_ is a bit mask of flags to be passed to the "splice" system call.
> +
> +The _tracefs_trace_pipe_print()_ function is similar to _tracefs_trace_pipe_stream()_, but
> +the stream of trace data is redirected to stdout.
> +
> +
> +RETURN VALUE
> +------------
> +The _tracefs_trace_pipe_stream()_, and _tracefs_trace_pipe_print()_ functions return 0 if the operation is
> +successful, or -1 in case of an error.
> +
> +EXAMPLE
> +-------
> +[source,c]
> +--
> +#include <unistd.h>
> +#include <signal.h>
> +
> +#include <tracefs.h>
> +
> +void stop(int sig)
> +{
> +	tracefs_trace_pipe_stop(NULL);
> +}
> +
> +int main()
> +{
> +	mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
> +	const char *filename = "trace.txt";
> +	int fd = creat(filename, mode);
> +	int ret;
> +
> +	signal(SIGINT, stop);
> +	ret = tracefs_trace_pipe_stream(fd, NULL, 0);
> +	close(fd);
> +
> +	return ret;
> +}
> +--
> +FILES
> +-----
> +[verse]
> +--
> +*tracefs.h*
> +	Header file to include in order to have access to the library APIs.
> +*-ltracefs*
> +	Linker switch to add when building a program that uses the library.
> +--
> +
> +SEE ALSO
> +--------
> +_libtracefs(3)_,
> +_libtraceevent(3)_,
> +_trace-cmd(1)_,
> +Documentation/trace/ftrace.rst from the Linux kernel tree
> +
> +AUTHOR
> +------
> +[verse]
> +--
> +*Steven Rostedt* <rostedt@goodmis.org>
> +*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
> +--
> +REPORTING BUGS
> +--------------
> +Report bugs to  <linux-trace-devel@vger.kernel.org>
> +
> +LICENSE
> +-------
> +libtracefs is Free Software licensed under the GNU LGPL 2.1
> +
> +RESOURCES
> +---------
> +https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
> +
> +COPYING
> +-------
> +Copyright \(C) 2021 VMware, Inc. Free use of this software is granted under
> +the terms of the GNU Public License (GPL).
> diff --git a/include/tracefs-local.h b/include/tracefs-local.h
> index 9e3aa18..833f136 100644
> --- a/include/tracefs-local.h
> +++ b/include/tracefs-local.h
> @@ -30,6 +30,7 @@ struct tracefs_instance {
>  	int				ftrace_notrace_fd;
>  	int				ftrace_marker_fd;
>  	int				ftrace_marker_raw_fd;
> +	int				pipe_keep_going;
>  };
>  
>  extern pthread_mutex_t toplevel_lock;
> diff --git a/include/tracefs.h b/include/tracefs.h
> index e29b550..3c6741b 100644
> --- a/include/tracefs.h
> +++ b/include/tracefs.h
> @@ -184,4 +184,9 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
>  /* Control library logs */
>  void tracefs_set_loglevel(enum tep_loglevel level);
>  
> +int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
> +int tracefs_trace_pipe_print(struct tracefs_instance *instance);
> +void tracefs_trace_pipe_stop(struct tracefs_instance *instance);
> +
> +
>  #endif /* _TRACE_FS_H */
> diff --git a/src/tracefs-tools.c b/src/tracefs-tools.c
> index 0cbb56d..0c0c44f 100644
> --- a/src/tracefs-tools.c
> +++ b/src/tracefs-tools.c
> @@ -912,3 +912,101 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
>  	tracefs_put_tracing_file(filter_path);
>  	return ret;
>  }
> +
> +static int top_pipe_keep_going;
> +
> +/**
> + * tracefs_trace_pipe_stream - redirect the stream of trace data to an output
> + * file. The "splice" system call is used to moves the data without copying
> + * between kernel address space and user address space. The user can interrupt
> + * the streaming of the data by pressing Ctrl-c.
> + * @fd: The file descriptor of the output file.
> + * @instance: ftrace instance, can be NULL for top tracing instance.
> + * @flags: flags to be passed to the "splice" system call.
> + *
> + * Returns -1 in case of an error or 0 otherwise.
> + */
> +int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance,
> +			      int flags)
> +{
> +	int *keep_going = instance ? &instance->pipe_keep_going :
> +				     &top_pipe_keep_going;

I'm thinking we should invert the above. That is, have a stop instead of
"keep_going", where it is false by default (when the instance is created).

That's because, if we start here, and the SIGINT comes in before we get
here, it keep_going might get set to false, and missed.

> +	const char *file = "trace_pipe";
> +	int brass[2], in_fd, ret = -1;
> +	off_t data_size;
> +
> +	in_fd = tracefs_instance_file_open(instance, file, O_RDONLY);
> +	if (in_fd < 0) {
> +		tracefs_warning("Failed to open 'trace_pipe'.");
> +		return ret;
> +	}
> +
> +	if(pipe(brass) < 0) {
> +		tracefs_warning("Failed to open pipe.");
> +		goto close_file;
> +	}
> +
> +	data_size = fcntl(brass[0], F_GETPIPE_SZ);
> +	if (data_size <= 0) {
> +		tracefs_warning("Failed to open pipe (size=0).");
> +		goto close_all;
> +	}
> +
> +	*keep_going = true;

Then we get here and we set it back to true.

Perhaps we should have a:

	instance->pipe_stop

flag that gets set by the user.

And instead of setting the variable here, add a,

   tracefs_trace_pipe_start(instance)

to match the tracefs_trace_pipe_stop().

If the user stops it, we should make it so that they need to start it again.

-- Steve


> +	while (*keep_going) {
> +		ret = splice(in_fd, NULL,
> +			     brass[1], NULL,
> +			     data_size, flags);
> +		if (ret < 0)
> +			break;
> +
> +		ret = splice(brass[0], NULL,
> +			     fd, NULL,
> +			     data_size, flags);
> +		if (ret < 0)
> +			break;
> +	}
> +
> +	/*
> +	 * Do not return error in the case when the "splice" system call
> +	 * was interrupted by the user (pressing Ctrl-c).
> +	 */
> +	if (!keep_going)
> +		ret = 0;
> +
> + close_all:
> +	close(brass[0]);
> +	close(brass[1]);
> + close_file:
> +	close(in_fd);
> +
> +	return ret;
> +}
> +
> +/**
> + * tracefs_trace_pipe_print - redirect the stream of trace data to "stdout".
> + * The "splice" system call is used to moves the data without copying
> + * between kernel address space and user address space.
> + * @instance: ftrace instance, can be NULL for top tracing instance.
> + *
> + * Returns -1 in case of an error or 0 otherwise.
> + */
> +
> +int tracefs_trace_pipe_print(struct tracefs_instance *instance)
> +{
> +   return tracefs_trace_pipe_stream(STDOUT_FILENO,
> +				    instance,
> +				    SPLICE_F_MORE | SPLICE_F_MOVE);
> +}
> +
> +/**
> + * tracefs_trace_pipe_stop - stop the streaming of trace data.
> + * @instance: ftrace instance, can be NULL for top tracing instance.
> + */
> +void tracefs_trace_pipe_stop(struct tracefs_instance *instance)
> +{
> +	if (instance)
> +		instance->pipe_keep_going = false;
> +	else
> +		top_pipe_keep_going = false;
> +}

Re: [PATCH v2] libtracefs: Add APIs for data streaming

[Yordan Karadzhov]

On 23.06.21 г. 15:45, Steven Rostedt wrote:
> On Wed, 23 Jun 2021 15:05:26 +0300
> "Yordan Karadzhov (VMware)" <y.karadz@gmail.com> wrote:
> 
>> The new APIs can be used to dump the content of "trace_pipe" into a
>> file or directly to "stdout". The "splice" system call is used to
>> moves the data without copying. The new functionality is essentially
>> identical to what 'trace-cmd show -p' does.
>>
>> Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
>> ---
>>
>> Changes in v2:
>>    - The setting of the signal disposition is removed from the library
>>      and is now responsibility of the caller. This in fact gives more
>>      options for the user.
>>    - The example provided in the documentation is updated accordingly.
>>
>>   Documentation/libtracefs-stream.txt | 106 ++++++++++++++++++++++++++++
>>   include/tracefs-local.h             |   1 +
>>   include/tracefs.h                   |   5 ++
>>   src/tracefs-tools.c                 |  98 +++++++++++++++++++++++++
>>   4 files changed, 210 insertions(+)
>>   create mode 100644 Documentation/libtracefs-stream.txt
>>
>> diff --git a/Documentation/libtracefs-stream.txt b/Documentation/libtracefs-stream.txt
>> new file mode 100644
>> index 0000000..24c2e47
>> --- /dev/null
>> +++ b/Documentation/libtracefs-stream.txt
>> @@ -0,0 +1,106 @@
>> +libtracefs(3)
>> +=============
>> +
>> +NAME
>> +----
>> +tracefs_trace_pipe_stream, tracefs_trace_pipe_print -
>> +redirect the stream of trace data to an output or stdout.
>> +
>> +SYNOPSIS
>> +--------
>> +[verse]
>> +--
>> +*#include <tracefs.h>*
>> +
>> +int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
>> +int tracefs_trace_pipe_print(struct tracefs_instance *instance);
>> +
>> +--
>> +
>> +DESCRIPTION
>> +-----------
>> +If NULL is passed as _instance_, the top trace instance is used.
>> +The user can interrupt the streaming of the data by pressing Ctrl-c.
>> +
>> +The _tracefs_trace_pipe_stream()_ function redirects the stream of trace data to an output
>> +file. The "splice" system call is used to moves the data without copying between kernel
>> +address space and user address space. The _fd_ is the file descriptor of the output file
>> +and _flags_ is a bit mask of flags to be passed to the "splice" system call.
>> +
>> +The _tracefs_trace_pipe_print()_ function is similar to _tracefs_trace_pipe_stream()_, but
>> +the stream of trace data is redirected to stdout.
>> +
>> +
>> +RETURN VALUE
>> +------------
>> +The _tracefs_trace_pipe_stream()_, and _tracefs_trace_pipe_print()_ functions return 0 if the operation is
>> +successful, or -1 in case of an error.
>> +
>> +EXAMPLE
>> +-------
>> +[source,c]
>> +--
>> +#include <unistd.h>
>> +#include <signal.h>
>> +
>> +#include <tracefs.h>
>> +
>> +void stop(int sig)
>> +{
>> +	tracefs_trace_pipe_stop(NULL);
>> +}
>> +
>> +int main()
>> +{
>> +	mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
>> +	const char *filename = "trace.txt";
>> +	int fd = creat(filename, mode);
>> +	int ret;
>> +
>> +	signal(SIGINT, stop);
>> +	ret = tracefs_trace_pipe_stream(fd, NULL, 0);
>> +	close(fd);
>> +
>> +	return ret;
>> +}
>> +--
>> +FILES
>> +-----
>> +[verse]
>> +--
>> +*tracefs.h*
>> +	Header file to include in order to have access to the library APIs.
>> +*-ltracefs*
>> +	Linker switch to add when building a program that uses the library.
>> +--
>> +
>> +SEE ALSO
>> +--------
>> +_libtracefs(3)_,
>> +_libtraceevent(3)_,
>> +_trace-cmd(1)_,
>> +Documentation/trace/ftrace.rst from the Linux kernel tree
>> +
>> +AUTHOR
>> +------
>> +[verse]
>> +--
>> +*Steven Rostedt* <rostedt@goodmis.org>
>> +*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
>> +--
>> +REPORTING BUGS
>> +--------------
>> +Report bugs to  <linux-trace-devel@vger.kernel.org>
>> +
>> +LICENSE
>> +-------
>> +libtracefs is Free Software licensed under the GNU LGPL 2.1
>> +
>> +RESOURCES
>> +---------
>> +https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
>> +
>> +COPYING
>> +-------
>> +Copyright \(C) 2021 VMware, Inc. Free use of this software is granted under
>> +the terms of the GNU Public License (GPL).
>> diff --git a/include/tracefs-local.h b/include/tracefs-local.h
>> index 9e3aa18..833f136 100644
>> --- a/include/tracefs-local.h
>> +++ b/include/tracefs-local.h
>> @@ -30,6 +30,7 @@ struct tracefs_instance {
>>   	int				ftrace_notrace_fd;
>>   	int				ftrace_marker_fd;
>>   	int				ftrace_marker_raw_fd;
>> +	int				pipe_keep_going;
>>   };
>>   
>>   extern pthread_mutex_t toplevel_lock;
>> diff --git a/include/tracefs.h b/include/tracefs.h
>> index e29b550..3c6741b 100644
>> --- a/include/tracefs.h
>> +++ b/include/tracefs.h
>> @@ -184,4 +184,9 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
>>   /* Control library logs */
>>   void tracefs_set_loglevel(enum tep_loglevel level);
>>   
>> +int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
>> +int tracefs_trace_pipe_print(struct tracefs_instance *instance);
>> +void tracefs_trace_pipe_stop(struct tracefs_instance *instance);
>> +
>> +
>>   #endif /* _TRACE_FS_H */
>> diff --git a/src/tracefs-tools.c b/src/tracefs-tools.c
>> index 0cbb56d..0c0c44f 100644
>> --- a/src/tracefs-tools.c
>> +++ b/src/tracefs-tools.c
>> @@ -912,3 +912,101 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
>>   	tracefs_put_tracing_file(filter_path);
>>   	return ret;
>>   }
>> +
>> +static int top_pipe_keep_going;
>> +
>> +/**
>> + * tracefs_trace_pipe_stream - redirect the stream of trace data to an output
>> + * file. The "splice" system call is used to moves the data without copying
>> + * between kernel address space and user address space. The user can interrupt
>> + * the streaming of the data by pressing Ctrl-c.
>> + * @fd: The file descriptor of the output file.
>> + * @instance: ftrace instance, can be NULL for top tracing instance.
>> + * @flags: flags to be passed to the "splice" system call.
>> + *
>> + * Returns -1 in case of an error or 0 otherwise.
>> + */
>> +int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance,
>> +			      int flags)
>> +{
>> +	int *keep_going = instance ? &instance->pipe_keep_going :
>> +				     &top_pipe_keep_going;
> 
> I'm thinking we should invert the above. That is, have a stop instead of
> "keep_going", where it is false by default (when the instance is created).
> 
> That's because, if we start here, and the SIGINT comes in before we get
> here, it keep_going might get set to false, and missed.

I intentionally tried to avoid having any dependency of the initialization value of the "keep_going" flag. We have to 
consider the case when the user creates one instance and then calls this function multiple times in a row.


> 
>> +	const char *file = "trace_pipe";
>> +	int brass[2], in_fd, ret = -1;
>> +	off_t data_size;
>> +
>> +	in_fd = tracefs_instance_file_open(instance, file, O_RDONLY);
>> +	if (in_fd < 0) {
>> +		tracefs_warning("Failed to open 'trace_pipe'.");
>> +		return ret;
>> +	}
>> +
>> +	if(pipe(brass) < 0) {
>> +		tracefs_warning("Failed to open pipe.");
>> +		goto close_file;
>> +	}
>> +
>> +	data_size = fcntl(brass[0], F_GETPIPE_SZ);
>> +	if (data_size <= 0) {
>> +		tracefs_warning("Failed to open pipe (size=0).");
>> +		goto close_all;
>> +	}
>> +
>> +	*keep_going = true;
> 
> Then we get here and we set it back to true.
> 
> Perhaps we should have a:
> 
> 	instance->pipe_stop
> 
> flag that gets set by the user.
> 
> And instead of setting the variable here, add a,
> 
>     tracefs_trace_pipe_start(instance)
> 
> to match the tracefs_trace_pipe_stop().
> 
> If the user stops it, we should make it so that they need to start it again.

I do not understand your point with the "start" function. tracefs_trace_pipe_stream() itself is the start.

Thanks!
Yordan


> 
> -- Steve
> 
> 
>> +	while (*keep_going) {
>> +		ret = splice(in_fd, NULL,
>> +			     brass[1], NULL,
>> +			     data_size, flags);
>> +		if (ret < 0)
>> +			break;
>> +
>> +		ret = splice(brass[0], NULL,
>> +			     fd, NULL,
>> +			     data_size, flags);
>> +		if (ret < 0)
>> +			break;
>> +	}
>> +
>> +	/*
>> +	 * Do not return error in the case when the "splice" system call
>> +	 * was interrupted by the user (pressing Ctrl-c).
>> +	 */
>> +	if (!keep_going)
>> +		ret = 0;
>> +
>> + close_all:
>> +	close(brass[0]);
>> +	close(brass[1]);
>> + close_file:
>> +	close(in_fd);
>> +
>> +	return ret;
>> +}
>> +
>> +/**
>> + * tracefs_trace_pipe_print - redirect the stream of trace data to "stdout".
>> + * The "splice" system call is used to moves the data without copying
>> + * between kernel address space and user address space.
>> + * @instance: ftrace instance, can be NULL for top tracing instance.
>> + *
>> + * Returns -1 in case of an error or 0 otherwise.
>> + */
>> +
>> +int tracefs_trace_pipe_print(struct tracefs_instance *instance)
>> +{
>> +   return tracefs_trace_pipe_stream(STDOUT_FILENO,
>> +				    instance,
>> +				    SPLICE_F_MORE | SPLICE_F_MOVE);
>> +}
>> +
>> +/**
>> + * tracefs_trace_pipe_stop - stop the streaming of trace data.
>> + * @instance: ftrace instance, can be NULL for top tracing instance.
>> + */
>> +void tracefs_trace_pipe_stop(struct tracefs_instance *instance)
>> +{
>> +	if (instance)
>> +		instance->pipe_keep_going = false;
>> +	else
>> +		top_pipe_keep_going = false;
>> +}
> 

Re: [PATCH v2] libtracefs: Add APIs for data streaming

[Steven Rostedt]

On Wed, 23 Jun 2021 16:02:00 +0300
Yordan Karadzhov <y.karadz@gmail.com> wrote:

> > I'm thinking we should invert the above. That is, have a stop instead of
> > "keep_going", where it is false by default (when the instance is created).
> > 
> > That's because, if we start here, and the SIGINT comes in before we get
> > here, it keep_going might get set to false, and missed.  
> 
> I intentionally tried to avoid having any dependency of the initialization value of the "keep_going" flag. We have to 
> consider the case when the user creates one instance and then calls this function multiple times in a row.

If anything then, make it the first thing that gets done, and not just
before the loop.

That is:


+int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance,
+			      int flags)
+{
+	int *keep_going = instance ? &instance->pipe_keep_going :
+				     &top_pipe_keep_going;
+	const char *file = "trace_pipe";
+	int brass[2], in_fd, ret = -1;
+	off_t data_size;

	*keep_going = true;

+
+	in_fd = tracefs_instance_file_open(instance, file, O_RDONLY);
+	if (in_fd < 0) {
+		tracefs_warning("Failed to open 'trace_pipe'.");
+		return ret;
+	}
+
+	if(pipe(brass) < 0) {
+		tracefs_warning("Failed to open pipe.");
+		goto close_file;
+	}
+
+	data_size = fcntl(brass[0], F_GETPIPE_SZ);
+	if (data_size <= 0) {
+		tracefs_warning("Failed to open pipe (size=0).");
+		goto close_all;
+	}
+
+	*keep_going = true;

And not here.

+	while (*keep_going) {
+		ret = splice(in_fd, NULL,
+			     brass[1], NULL,
+			     data_size, flags);
+		if (ret < 0)
+			break;
+
+		ret = splice(brass[0], NULL,
+			     fd, NULL,
+			     data_size, flags);
+		if (ret < 0)
+			break;
+	}


And I think we need to make it volatile, otherwise the compiler is free to
ignore it. Because the compiler does not need to know about threads.

	*keep_going = true;
	while (*keep_going) {
		[ do something ]
	}

To the compiler that is the same as:

	while (1) {
		[ do something ]
	}

And is free to make that change when optimizing.

What needs to be done is:

	(*(volatile bool *)keep_going) = true;

and

	while (*(volatile bool *)keep_going) {

That way the compiler knows that the value can change from outside its
knowledge.

-- Steve

Re: [PATCH v2] libtracefs: Add APIs for data streaming

[Yordan Karadzhov]

On 23.06.21 г. 16:19, Steven Rostedt wrote:
> On Wed, 23 Jun 2021 16:02:00 +0300
> Yordan Karadzhov <y.karadz@gmail.com> wrote:
> 
>>> I'm thinking we should invert the above. That is, have a stop instead of
>>> "keep_going", where it is false by default (when the instance is created).
>>>
>>> That's because, if we start here, and the SIGINT comes in before we get
>>> here, it keep_going might get set to false, and missed.
>>
>> I intentionally tried to avoid having any dependency of the initialization value of the "keep_going" flag. We have to
>> consider the case when the user creates one instance and then calls this function multiple times in a row.
> 
> If anything then, make it the first thing that gets done, and not just
> before the loop.
> 
> That is:
> 
> 
> +int tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance,
> +			      int flags)
> +{
> +	int *keep_going = instance ? &instance->pipe_keep_going :
> +				     &top_pipe_keep_going;
> +	const char *file = "trace_pipe";
> +	int brass[2], in_fd, ret = -1;
> +	off_t data_size;
> 
> 	*keep_going = true;
> 
> +
> +	in_fd = tracefs_instance_file_open(instance, file, O_RDONLY);
> +	if (in_fd < 0) {
> +		tracefs_warning("Failed to open 'trace_pipe'.");
> +		return ret;
> +	}
> +
> +	if(pipe(brass) < 0) {
> +		tracefs_warning("Failed to open pipe.");
> +		goto close_file;
> +	}
> +
> +	data_size = fcntl(brass[0], F_GETPIPE_SZ);
> +	if (data_size <= 0) {
> +		tracefs_warning("Failed to open pipe (size=0).");
> +		goto close_all;
> +	}
> +
> +	*keep_going = true;
> 
> And not here.
> 
> +	while (*keep_going) {
> +		ret = splice(in_fd, NULL,
> +			     brass[1], NULL,
> +			     data_size, flags);
> +		if (ret < 0)
> +			break;
> +
> +		ret = splice(brass[0], NULL,
> +			     fd, NULL,
> +			     data_size, flags);
> +		if (ret < 0)
> +			break;
> +	}
> 
> 
> And I think we need to make it volatile, otherwise the compiler is free to
> ignore it. Because the compiler does not need to know about threads.
> 
> 	*keep_going = true;
> 	while (*keep_going) {
> 		[ do something ]
> 	}
> 
> To the compiler that is the same as:
> 
> 	while (1) {
> 		[ do something ]
> 	}
> 
> And is free to make that change when optimizing.
> 
> What needs to be done is:
> 
> 	(*(volatile bool *)keep_going) = true;
> 
> and
> 
> 	while (*(volatile bool *)keep_going) {
> 
> That way the compiler knows that the value can change from outside its
> knowledge.
> 

OK, I will make the changes and will send v3.

Thanks a lot!
Yordan

> -- Steve
>