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[Qemu-block] [PATCH 3/5] trace: enable tracing in qemu-nbd

From: Denis V. Lunev
Subject: [Qemu-block] [PATCH 3/5] trace: enable tracing in qemu-nbd
Date: Thu, 2 Jun 2016 21:35:43 +0300

Please note, trace_init_backends() must be called in the final process,
i.e. after daemonization. This is necessary to keep tracing thread in
the proper process.

Signed-off-by: Denis V. Lunev <address@hidden>
CC: Eric Blake <address@hidden>
CC: Paolo Bonzini <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
CC: Kevin Wolf <address@hidden>
 qemu-nbd.c    | 18 +++++++++++++++++-
 qemu-nbd.texi | 28 ++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/qemu-nbd.c b/qemu-nbd.c
index 6554f0a..cd29164 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -27,12 +27,14 @@
 #include "qemu/error-report.h"
 #include "qemu/config-file.h"
 #include "qemu/bswap.h"
+#include "qemu/log.h"
 #include "block/snapshot.h"
 #include "qapi/util.h"
 #include "qapi/qmp/qstring.h"
 #include "qom/object_interfaces.h"
 #include "io/channel-socket.h"
 #include "crypto/init.h"
+#include "trace/control.h"
 #include <getopt.h>
 #include <libgen.h>
@@ -88,6 +90,8 @@ static void usage(const char *name)
 "General purpose options:\n"
 "  --object type,id=ID,...   define an object such as 'secret' for providing\n"
 "                            passwords and/or encryption keys\n"
+"  --trace [[enable=]<pattern>][,events=<file>][,file=<file>]\n"
+"                            specify tracing options\n"
 #ifdef __linux__
 "Kernel NBD client support:\n"
 "  -c, --connect=DEV         connect FILE to the local NBD device DEV\n"
@@ -470,7 +474,7 @@ int main(int argc, char **argv)
     off_t fd_size;
     QemuOpts *sn_opts = NULL;
     const char *sn_id_or_name = NULL;
-    const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:tl:x:";
+    const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:tl:x:T:";
     struct option lopt[] = {
         { "help", no_argument, NULL, 'h' },
         { "version", no_argument, NULL, 'V' },
@@ -498,6 +502,7 @@ int main(int argc, char **argv)
         { "export-name", required_argument, NULL, 'x' },
         { "tls-creds", required_argument, NULL, QEMU_NBD_OPT_TLSCREDS },
         { "image-opts", no_argument, NULL, QEMU_NBD_OPT_IMAGE_OPTS },
+        { "trace", required_argument, NULL, 'T' },
         { NULL, 0, NULL, 0 }
     int ch;
@@ -518,6 +523,7 @@ int main(int argc, char **argv)
     const char *tlscredsid = NULL;
     bool imageOpts = false;
     bool writethrough = true;
+    char *trace_file = NULL;
     /* The client thread uses SIGTERM to interrupt the server.  A signal
      * handler ensures that "qemu-nbd -v -c" exits with a nice status code.
@@ -531,6 +537,7 @@ int main(int argc, char **argv)
+    qemu_add_opts(&qemu_trace_opts);
     while ((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
@@ -703,6 +710,9 @@ int main(int argc, char **argv)
         case QEMU_NBD_OPT_IMAGE_OPTS:
             imageOpts = true;
+        case 'T':
+            trace_file = trace_opt_parse(optarg, trace_file);
+            break;
@@ -718,6 +728,12 @@ int main(int argc, char **argv)
+    if (!trace_init_backends()) {
+        exit(1);
+    }
+    trace_init_file(trace_file);
+    qemu_set_log(LOG_TRACE);
     if (tlscredsid) {
         if (sockpath) {
             error_report("TLS is only supported with IPv4/IPv6");
diff --git a/qemu-nbd.texi b/qemu-nbd.texi
index 9f23343..e6943ad 100644
--- a/qemu-nbd.texi
+++ b/qemu-nbd.texi
@@ -92,6 +92,34 @@ Display extra debugging information
 Display this help and exit
 @item -V, --version
 Display version information and exit
address@hidden -T, --trace address@hidden,address@hidden
address@hidden --trace
+Specify tracing options.
address@hidden @option
address@hidden address@hidden
+Immediately enable events matching @var{pattern}.
+The file must contain one event name (as listed in the @file{trace-events} 
+per line; globbing patterns are accepted too.  This option is only
+available if QEMU NBD has been compiled with the @var{simple}, @var{stderr}
+or @var{ftrace} tracing backend.  To specify multiple events or patterns,
+specify the @option{--trace} option multiple times.
+Use @code{--trace help} to print a list of names of trace points.
address@hidden address@hidden
+Immediately enable events listed in @var{file}.
+The file must contain one event name (as listed in the @file{trace-events} 
+per line; globbing patterns are accepted too.  This option is only
+available if QEMU NBD has been compiled with the @var{simple}, @var{stderr} or
address@hidden tracing backend.
address@hidden address@hidden
+Log output traces to @var{file}.
+This option is only available if QEMU NBD has been compiled with
+the @var{simple} tracing backend.
address@hidden table
 @end table
 @c man end

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