[Qemu-devel] [PATCH 4/5] trace-cmd: Add non-blocking option for open() and splice_read()

[Yoshihiro YUNOMAE]

Add non-blocking option for open() and splice_read() for avoiding block to read
trace data of a guest from FIFO.

If SIGINT comes to read/write processes from the parent process in the case
where FIFO as a read I/F is assigned, then reading is normally blocked for
splice_read(). So, we added nonblock option to open() and splice_read().

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

 trace-recorder.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/trace-recorder.c b/trace-recorder.c
index 3b750e9..6577fe8 100644
--- a/trace-recorder.c
+++ b/trace-recorder.c
@@ -124,7 +124,7 @@ struct tracecmd_recorder *tracecmd_create_recorder_fd(int 
fd, int cpu)
                goto out_free;
 
        sprintf(path, "%s/per_cpu/cpu%d/trace_pipe_raw", tracing, cpu);
-       recorder->trace_fd = open(path, O_RDONLY);
+       recorder->trace_fd = open(path, O_RDONLY | O_NONBLOCK);
        if (recorder->trace_fd < 0)
                goto out_free;
 
@@ -172,14 +172,17 @@ static long splice_data(struct tracecmd_recorder 
*recorder)
        long ret;
 
        ret = splice(recorder->trace_fd, NULL, recorder->brass[1], NULL,
-                    recorder->page_size, 1 /* SPLICE_F_MOVE */);
+                    recorder->page_size, SPLICE_F_MOVE | SPLICE_F_NONBLOCK);
        if (ret < 0) {
-               warning("recorder error in splice input");
-               return -1;
+               if (errno != EAGAIN) {
+                       warning("recorder error in splice input");
+                       return -1;
+               }
+               return 0; /* Buffer is empty */
        }
 
        ret = splice(recorder->brass[0], NULL, recorder->fd, NULL,
-                    recorder->page_size, 3 /* and NON_BLOCK */);
+                    recorder->page_size, SPLICE_F_MOVE | SPLICE_F_NONBLOCK);
        if (ret < 0) {
                if (errno != EAGAIN) {
                        warning("recorder error in splice output");