[PATCH v2 2/5] libtracefs: Add tracefs_cpu_create_fd()

[Steven Rostedt <rostedt@xxxxxxxxxxx>]

From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>

Add tracefs_cpu_create_fd() to attach a tracefs_cpu descriptor to an
already opened file descriptor.

Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 include/tracefs.h    |  1 +
 src/tracefs-record.c | 94 +++++++++++++++++++++++++++++---------------
 2 files changed, 64 insertions(+), 31 deletions(-)

diff --git a/include/tracefs.h b/include/tracefs.h
index f500cb47c372..449bfd04a395 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -597,6 +597,7 @@ tracefs_synth_get_event(struct tep_handle *tep, struct tracefs_synth *synth);
 
 struct tracefs_cpu;
 
+struct tracefs_cpu *tracefs_cpu_create_fd(int fd, int subbuf_size, bool nonblock);
 struct tracefs_cpu *tracefs_cpu_open(struct tracefs_instance *instance,
 				     int cpu, bool nonblock);
 void tracefs_cpu_close(struct tracefs_cpu *tcpu);
diff --git a/src/tracefs-record.c b/src/tracefs-record.c
index a59614de05ab..fdc470d71f1e 100644
--- a/src/tracefs-record.c
+++ b/src/tracefs-record.c
@@ -24,7 +24,6 @@ enum {
 };
 
 struct tracefs_cpu {
-	int		cpu;
 	int		fd;
 	int		flags;
 	int		nfds;
@@ -37,25 +36,21 @@ struct tracefs_cpu {
 };
 
 /**
- * tracefs_cpu_open - open an instance raw trace file
- * @instance: the instance (NULL for toplevel) of the cpu raw file to open
- * @cpu: The CPU that the raw trace file is associated with
+ * tracefs_cpu_create_fd - create a tracefs_cpu instance for an existing fd
+ * @fd: The file descriptor to attach the tracefs_cpu to
+ * @subbuf_size: The expected size to read the subbuffer with
  * @nonblock: If true, the file will be opened in O_NONBLOCK mode
  *
  * Return a descriptor that can read the tracefs trace_pipe_raw file
- * for a give @cpu in a given @instance.
+ * that is associated with the given @fd and must be read in @subbuf_size.
  *
  * Returns NULL on error.
  */
 struct tracefs_cpu *
-tracefs_cpu_open(struct tracefs_instance *instance, int cpu, bool nonblock)
+tracefs_cpu_create_fd(int fd, int subbuf_size, bool nonblock)
 {
 	struct tracefs_cpu *tcpu;
-	struct tep_handle *tep;
 	int mode = O_RDONLY;
-	char path[128];
-	char *buf;
-	int len;
 	int ret;
 
 	tcpu = calloc(1, sizeof(*tcpu));
@@ -70,14 +65,62 @@ tracefs_cpu_open(struct tracefs_instance *instance, int cpu, bool nonblock)
 	tcpu->splice_pipe[0] = -1;
 	tcpu->splice_pipe[1] = -1;
 
+	tcpu->fd = fd;
+
+	tcpu->subbuf_size = subbuf_size;
+
+	if (tcpu->flags & TC_NONBLOCK) {
+		tcpu->ctrl_pipe[0] = -1;
+		tcpu->ctrl_pipe[1] = -1;
+	} else {
+		/* ctrl_pipe is used to break out of blocked reads */
+		ret = pipe(tcpu->ctrl_pipe);
+		if (ret < 0)
+			goto fail;
+		if (tcpu->ctrl_pipe[0] > tcpu->fd)
+			tcpu->nfds = tcpu->ctrl_pipe[0] + 1;
+		else
+			tcpu->nfds = tcpu->fd + 1;
+	}
+
+	return tcpu;
+ fail:
+	free(tcpu);
+	return NULL;
+}
+
+/**
+ * tracefs_cpu_open - open an instance raw trace file
+ * @instance: the instance (NULL for toplevel) of the cpu raw file to open
+ * @cpu: The CPU that the raw trace file is associated with
+ * @nonblock: If true, the file will be opened in O_NONBLOCK mode
+ *
+ * Return a descriptor that can read the tracefs trace_pipe_raw file
+ * for a give @cpu in a given @instance.
+ *
+ * Returns NULL on error.
+ */
+struct tracefs_cpu *
+tracefs_cpu_open(struct tracefs_instance *instance, int cpu, bool nonblock)
+{
+	struct tracefs_cpu *tcpu;
+	struct tep_handle *tep;
+	char path[128];
+	char *buf;
+	int mode = O_RDONLY;
+	int subbuf_size;
+	int len;
+	int ret;
+	int fd;
+
+	if (nonblock)
+		mode |= O_NONBLOCK;
+
 	sprintf(path, "per_cpu/cpu%d/trace_pipe_raw", cpu);
 
-	tcpu->cpu = cpu;
-	tcpu->fd = tracefs_instance_file_open(instance, path, mode);
-	if (tcpu->fd < 0) {
-		free(tcpu);
+	fd = tracefs_instance_file_open(instance, path, mode);
+	if (fd < 0)
 		return NULL;
-	}
 
 	tep = tep_alloc();
 	if (!tep)
@@ -93,29 +136,18 @@ tracefs_cpu_open(struct tracefs_instance *instance, int cpu, bool nonblock)
 	if (ret < 0)
 		goto fail;
 
-	tcpu->subbuf_size = tep_get_sub_buffer_size(tep);
+	subbuf_size = tep_get_sub_buffer_size(tep);
 	tep_free(tep);
 	tep = NULL;
 
-	if (tcpu->flags & TC_NONBLOCK) {
-		tcpu->ctrl_pipe[0] = -1;
-		tcpu->ctrl_pipe[1] = -1;
-	} else {
-		/* ctrl_pipe is used to break out of blocked reads */
-		ret = pipe(tcpu->ctrl_pipe);
-		if (ret < 0)
-			goto fail;
-		if (tcpu->ctrl_pipe[0] > tcpu->fd)
-			tcpu->nfds = tcpu->ctrl_pipe[0] + 1;
-		else
-			tcpu->nfds = tcpu->fd + 1;
-	}
+	tcpu = tracefs_cpu_create_fd(fd, subbuf_size, nonblock);
+	if (!tcpu)
+		goto fail;
 
 	return tcpu;
  fail:
 	tep_free(tep);
-	close(tcpu->fd);
-	free(tcpu);
+	close(fd);
 	return NULL;
 }
 
-- 
2.35.1