[Qemu-devel] [PATCH 3/5] trace-cmd: Support trace-agent of virtio-trace

[Yoshihiro YUNOMAE]

Add read path and control path to use trace-agent of virtio-trace.
When we use trace-agent, trace-cmd will be used as follows:
        # AGENT_READ_DIR=/tmp/virtio-trace/tracing \
          AGENT_CTL=/tmp/virtio-trace/agent-ctl-path.in \
          TRACING_DIR=/tmp/virtio-trace/debugfs/tracing \
          trace-cmd record -e "sched:*"
Here, AGENT_READ_DIR is the path for a reading directory of virtio-trace,
AGENT_CTL is a control path of trace-agent, and TRACING_DIR is a debugfs path
of a guest.

Signed-off-by: Yoshihiro YUNOMAE <address@hidden>
---

 trace-cmd.h      |    1 +
 trace-recorder.c |   57 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 trace-util.c     |   18 +++++++++++++++++
 3 files changed, 75 insertions(+), 1 deletions(-)

diff --git a/trace-cmd.h b/trace-cmd.h
index f904dc5..75506ed 100644
--- a/trace-cmd.h
+++ b/trace-cmd.h
@@ -72,6 +72,7 @@ static inline int tracecmd_host_bigendian(void)
 }
 
 char *tracecmd_find_tracing_dir(void);
+char *guest_agent_tracing_read_dir(void);
 
 /* --- Opening and Reading the trace.dat file --- */
 
diff --git a/trace-recorder.c b/trace-recorder.c
index 215affc..3b750e9 100644
--- a/trace-recorder.c
+++ b/trace-recorder.c
@@ -33,6 +33,7 @@
 #include <unistd.h>
 #include <ctype.h>
 #include <errno.h>
+#include <stdbool.h>
 
 #include "trace-cmd.h"
 
@@ -43,6 +44,8 @@ struct tracecmd_recorder {
        int             page_size;
        int             cpu;
        int             stop;
+       int             ctl_fd;
+       bool            agent_existing;
 };
 
 void tracecmd_free_recorder(struct tracecmd_recorder *recorder)
@@ -59,11 +62,29 @@ void tracecmd_free_recorder(struct tracecmd_recorder 
*recorder)
        free(recorder);
 }
 
+static char *use_trace_agent_dir(char *ctl_path,
+                                       struct tracecmd_recorder *recorder)
+{
+       ctl_path = strdup(ctl_path);
+       if (!ctl_path)
+               die("malloc");
+       warning("Use environmental control path: %s\n", ctl_path);
+
+       recorder->ctl_fd = open(ctl_path, O_WRONLY);
+       if (recorder->ctl_fd < 0)
+               return NULL;
+
+       recorder->agent_existing = true;
+
+       return guest_agent_tracing_read_dir();
+}
+
 struct tracecmd_recorder *tracecmd_create_recorder_fd(int fd, int cpu)
 {
        struct tracecmd_recorder *recorder;
        char *tracing = NULL;
        char *path = NULL;
+       char *ctl_path = NULL;
        int ret;
 
        recorder = malloc_or_die(sizeof(*recorder));
@@ -76,12 +97,23 @@ struct tracecmd_recorder *tracecmd_create_recorder_fd(int 
fd, int cpu)
        recorder->trace_fd = -1;
        recorder->brass[0] = -1;
        recorder->brass[1] = -1;
+       recorder->ctl_fd = -1;
+       recorder->agent_existing = false;
 
        recorder->page_size = getpagesize();
 
        recorder->fd = fd;
 
-       tracing = tracecmd_find_tracing_dir();
+       /*
+        * The trace-agent on a guest is controlled to run or stop by a host,
+        * so we need to assign the control path of the trace-agent to use
+        * virtio-trace.
+        */
+       ctl_path = getenv("AGENT_CTL");
+       if (ctl_path)
+               tracing = use_trace_agent_dir(ctl_path, recorder);
+       else
+               tracing = tracecmd_find_tracing_dir();
        if (!tracing) {
                errno = ENODEV;
                goto out_free;
@@ -182,6 +214,24 @@ long tracecmd_flush_recording(struct tracecmd_recorder 
*recorder)
        return total;
 }
 
+static void operation_to_trace_agent(int ctl_fd, bool run_agent)
+{
+       if (run_agent == true)
+               write(ctl_fd, "1", 2);
+       else
+               write(ctl_fd, "0", 2);
+}
+
+static void run_operation_to_trace_agent(int ctl_fd)
+{
+       operation_to_trace_agent(ctl_fd, true);
+}
+
+static void stop_operation_to_trace_agent(int ctl_fd)
+{
+       operation_to_trace_agent(ctl_fd, false);
+}
+
 int tracecmd_start_recording(struct tracecmd_recorder *recorder, unsigned long 
sleep)
 {
        struct timespec req;
@@ -189,6 +239,9 @@ int tracecmd_start_recording(struct tracecmd_recorder 
*recorder, unsigned long s
 
        recorder->stop = 0;
 
+       if (recorder->agent_existing)
+               run_operation_to_trace_agent(recorder->ctl_fd);
+       
        do {
                if (sleep) {
                        req.tv_sec = sleep / 1000000;
@@ -214,6 +267,8 @@ void tracecmd_stop_recording(struct tracecmd_recorder 
*recorder)
        if (!recorder)
                return;
 
+       if (recorder->agent_existing)
+               stop_operation_to_trace_agent(recorder->ctl_fd);
        recorder->stop = 1;
 }
 
diff --git a/trace-util.c b/trace-util.c
index d5a3eb4..ff639be 100644
--- a/trace-util.c
+++ b/trace-util.c
@@ -304,6 +304,24 @@ static int mount_debugfs(void)
        return ret;
 }
 
+char *guest_agent_tracing_read_dir(void)
+{
+       char *tracing_read_dir;
+
+       tracing_read_dir = getenv("AGENT_READ_DIR");
+       if (tracing_read_dir) {
+               tracing_read_dir = strdup(tracing_read_dir);
+               if (!tracing_read_dir)
+                       die("malloc");
+               warning("Use environmental read directory of trace-agent: %s\n",
+                                                       tracing_read_dir);
+               return tracing_read_dir;
+       }
+
+       warning("AGENT_READ_DIR was not declared");
+       return NULL;
+}
+
 char *tracecmd_find_tracing_dir(void)
 {
        char debugfs[MAX_PATH+1];