[v3,3/8] libtracefs: Add tracefs_cpu_pipe()

Commit Message

Steven Rostedt Nov. 9, 2022, 11:52 p.m. UTC

From: "Steven Rostedt (Google)" <[e-mail]>

Add the interface to call splice directly from the tracefs_cpu descriptor.
The requirement is that either the passed in file descriptor is a pipe, or
that the tcpu was created with tracefs_cpu_create_fd() and the fd used
there was a pipe.

Signed-off-by: Steven Rostedt (Google) <[e-mail]>
---
 include/tracefs.h    |  2 +-
 src/tracefs-record.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

Patch

diff --git a/include/tracefs.h b/include/tracefs.h
index fd4f0668e7cc..9f0bdc62836a 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -609,6 +609,6 @@  int tracefs_cpu_write(struct tracefs_cpu *tcpu, int wfd, bool nonblock);
 int tracefs_cpu_stop(struct tracefs_cpu *tcpu);
 int tracefs_cpu_flush(struct tracefs_cpu *tcpu, void *buffer);
 int tracefs_cpu_flush_write(struct tracefs_cpu *tcpu, int wfd);
-
+int tracefs_cpu_pipe(struct tracefs_cpu *tcpu, int wfd, bool nonblock);
 
 #endif /* _TRACE_FS_H */
diff --git a/src/tracefs-record.c b/src/tracefs-record.c
index 4ef3a259a203..f5a72a08877d 100644
--- a/src/tracefs-record.c
+++ b/src/tracefs-record.c
@@ -547,3 +547,33 @@  int tracefs_cpu_write(struct tracefs_cpu *tcpu, int wfd, bool nonblock)
 
 	return tot_write;
 }
+
+/**
+ * tracefs_cpu_pipe - Write the raw trace file into a pipe descriptor
+ * @tcpu: The descriptor representing the raw trace file
+ * @wfd: The write file descriptor to write the data to (must be a pipe)
+ * @nonblock: Hint to not block on the read if there's no data.
+ *
+ * This will splice directly the file descriptor of the trace_pipe_raw
+ * file to the given @wfd, which must be a pipe. This can also be used
+ * if @tcpu was created with tracefs_cpu_create_fd() where the passed
+ * in @fd there was a pipe, then @wfd does not need to be a pipe.
+ *
+ * Returns the number of bytes read or negative on error.
+ */
+int tracefs_cpu_pipe(struct tracefs_cpu *tcpu, int wfd, bool nonblock)
+{
+	int mode = SPLICE_F_MOVE;
+	int ret;
+
+	ret = wait_on_input(tcpu, nonblock);
+	if (ret <= 0)
+		return ret;
+
+	if (nonblock || tcpu->flags & TC_NONBLOCK)
+		mode |= SPLICE_F_NONBLOCK;
+
+	ret = splice(tcpu->fd, NULL, wfd, NULL,
+		     tcpu->pipe_size, mode);
+	return ret;
+}