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@xxxxxxxxx>
---
Documentation/libtracefs-stream.txt | 93 +++++++++++++++++++++++++++++
include/tracefs.h | 4 ++
src/tracefs-tools.c | 92 ++++++++++++++++++++++++++++
3 files changed, 189 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..715cdfc
--- /dev/null
+++ b/Documentation/libtracefs-stream.txt
@@ -0,0 +1,93 @@
+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 <tracefs.h>
+
+int main(int argc, char **argv)
+{
+ mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
+ const char *filename = "./test.out";
+ int fd = creat(filename, mode);
+
+ return tracefs_trace_pipe_stream(fd, NULL, 0);
+}
+--
+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@xxxxxxxxxxx>
+*Tzvetomir Stoyanov* <tz.stoyanov@xxxxxxxxx>
+--
+REPORTING BUGS
+--------------
+Report bugs to <linux-trace-devel@xxxxxxxxxxxxxxx>
+
+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.h b/include/tracefs.h
index e29b550..f3c69da 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -184,4 +184,8 @@ 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);
+
#endif /* _TRACE_FS_H */
diff --git a/src/tracefs-tools.c b/src/tracefs-tools.c
index 0cbb56d..4874a44 100644
--- a/src/tracefs-tools.c
+++ b/src/tracefs-tools.c
@@ -15,6 +15,7 @@
#include <limits.h>
#include <pthread.h>
#include <errno.h>
+#include <signal.h>
#include "tracefs.h"
#include "tracefs-local.h"
@@ -912,3 +913,94 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
tracefs_put_tracing_file(filter_path);
return ret;
}
+
+static bool keep_going;
+
+static void finish(int sig)
+{
+ signal(SIGINT,SIG_DFL);
+ keep_going = false;
+}
+
+/**
+ * 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)
+{
+ 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;
+ }
+ signal(SIGINT, finish);
+ 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);
+}
--
2.27.0
|