perf record: auto detect when stdout is a pipe

This patch gives the ability to 'perf record' to detect when its stdout
has been redirected to a pipe. There's now no more need to add '-o -'
switch in this case.

However '-o <path>' option has always precedence, that is if specified
and stdout has been connected via a pipe then the output will go into
the specified output.

LKML-Reference: <m3ipxo966i.fsf@gmail.com>
Signed-off-by: Franck Bui-Huu <fbuihuu@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 20 insertions, 12 deletions

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 45a3689f9ed6..1346d4230bc0 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -48,7 +48,7 @@ static unsigned int		user_freq 			= UINT_MAX;
 static int                      freq                            =   1000;
 static int                      output;
 static int                      pipe_output                     =      0;
-static const char               *output_name                    = "perf.data";
+static const char               *output_name                    = NULL;
 static int                      group                           =      0;
 static int                      realtime_prio                   =      0;
 static bool                     nodelay                         =  false;
@@ -497,18 +497,26 @@ static int __cmd_record(int argc, const char **argv)
                 exit(-1);
         }
 
-        if (!strcmp(output_name, "-"))
-                pipe_output = 1;
-        else if (!stat(output_name, &st) && st.st_size) {
-                if (write_mode == WRITE_FORCE) {
-                        char oldname[PATH_MAX];
-                        snprintf(oldname, sizeof(oldname), "%s.old",
-                                 output_name);
-                        unlink(oldname);
-                        rename(output_name, oldname);
+        if (!output_name) {
+                if (!fstat(STDOUT_FILENO, &st) && S_ISFIFO(st.st_mode))
+                        pipe_output = 1;
+                else
+                        output_name = "perf.data";
+        }
+        if (output_name) {
+                if (!strcmp(output_name, "-"))
+                        pipe_output = 1;
+                else if (!stat(output_name, &st) && st.st_size) {
+                        if (write_mode == WRITE_FORCE) {
+                                char oldname[PATH_MAX];
+                                snprintf(oldname, sizeof(oldname), "%s.old",
+                                         output_name);
+                                unlink(oldname);
+                                rename(output_name, oldname);
+                        }
+                } else if (write_mode == WRITE_APPEND) {
+                        write_mode = WRITE_FORCE;
                 }
-        } else if (write_mode == WRITE_APPEND) {
-                write_mode = WRITE_FORCE;
         }
 
         flags = O_CREAT|O_RDWR;