From: "Yordan Karadzhov (VMware)" <y.karadz@xxxxxxxxx>
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>
[ Updated to fix writing to STDOUT ]
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
Documentation/libtracefs-stream.txt | 106 +++++++++++++++++++++
include/tracefs-local.h | 1 +
include/tracefs.h | 5 +
src/tracefs-tools.c | 140 ++++++++++++++++++++++++++++
4 files changed, 252 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..b9692e3
--- /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>*
+
+ssize_t tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
+ssize_t 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 the
+number of bytes transfered 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, SPLICE_F_NONBLOCK);
+ 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@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-local.h b/include/tracefs-local.h
index 9e3aa18..73698e8 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;
+ bool pipe_keep_going;
};
extern pthread_mutex_t toplevel_lock;
diff --git a/include/tracefs.h b/include/tracefs.h
index e29b550..23a3c7d 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);
+ssize_t tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance, int flags);
+ssize_t 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..1df3732 100644
--- a/src/tracefs-tools.c
+++ b/src/tracefs-tools.c
@@ -912,3 +912,143 @@ int tracefs_function_notrace(struct tracefs_instance *instance, const char *filt
tracefs_put_tracing_file(filter_path);
return ret;
}
+
+static bool 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 number of bytes transferred otherwise.
+ */
+ssize_t tracefs_trace_pipe_stream(int fd, struct tracefs_instance *instance,
+ int flags)
+{
+ bool *keep_going = instance ? &instance->pipe_keep_going :
+ &top_pipe_keep_going;
+ const char *file = "trace_pipe";
+ int brass[2], in_fd, ret = -1;
+ int oflags = flags & SPLICE_F_NONBLOCK ? O_NONBLOCK: 0;
+ off_t data_size;
+ ssize_t bread = 0;
+
+ (*(volatile bool *)keep_going) = true;
+
+ in_fd = tracefs_instance_file_open(instance, file, O_RDONLY | oflags);
+ 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;
+ }
+
+ errno = 0;
+
+ while (*(volatile bool *)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;
+ bread += ret;
+ }
+
+ /*
+ * Do not return error in the case when the "splice" system call
+ * was interrupted by the user (pressing Ctrl-c).
+ * Or if NONBLOCK was specified.
+ */
+ if (!keep_going || errno == EAGAIN || errno == EINTR)
+ ret = 0;
+
+ close_all:
+ close(brass[0]);
+ close(brass[1]);
+ close_file:
+ close(in_fd);
+
+ return ret ? ret : bread;
+}
+
+/**
+ * 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 number of bytes transferred otherwise.
+ */
+
+ssize_t tracefs_trace_pipe_print(struct tracefs_instance *instance)
+{
+ bool *keep_going = instance ? &instance->pipe_keep_going :
+ &top_pipe_keep_going;
+ char buf[BUFSIZ];
+ ssize_t bread = 0;
+ int brass[2];
+ int ret;
+
+ if(pipe(brass) < 0) {
+ tracefs_warning("Failed to open pipe.");
+ return -1;
+ }
+
+ errno = 0;
+ do {
+ ret = tracefs_trace_pipe_stream(brass[1],
+ instance,
+ SPLICE_F_MORE | SPLICE_F_MOVE |
+ SPLICE_F_NONBLOCK);
+ if (ret < 0 && errno != EAGAIN && errno != EINTR)
+ break;
+
+ if (!ret)
+ break;
+
+ ret = read(brass[0], buf, BUFSIZ);
+ if (ret < 0 && errno == EAGAIN)
+ ret = 0;
+ if (ret > 0) {
+ ret = write(STDOUT_FILENO, buf, ret);
+ if (ret > 0)
+ bread += ret;
+ }
+ } while (ret > 0 && *(volatile bool *)keep_going);
+
+ close(brass[0]);
+ close(brass[1]);
+
+ return ret < 0 ? ret : bread;
+}
+
+/**
+ * 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;
+}
--
2.30.2
|