perf evlist: Introduce {prepare,start}_workload refactored from 'perf record'

So that we can easily start a workload in other tools.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-zdsksd4aphu0nltg2lpwsw3x@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

2 files changed, 106 insertions, 0 deletions

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index b774341e797f..a472247af191 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -13,6 +13,7 @@
 #include "thread_map.h"
 #include "evlist.h"
 #include "evsel.h"
+#include <unistd.h>
 
 #include "parse-events.h"
 
@@ -33,6 +34,7 @@ void perf_evlist__init(struct perf_evlist *evlist, struct cpu_map *cpus,
 		INIT_HLIST_HEAD(&evlist->heads[i]);
 	INIT_LIST_HEAD(&evlist->entries);
 	perf_evlist__set_maps(evlist, cpus, threads);
+	evlist->workload.pid = -1;
 }
 
 struct perf_evlist *perf_evlist__new(struct cpu_map *cpus,
@@ -674,3 +676,97 @@ out_err:
 
 	return err;
 }
+
+int perf_evlist__prepare_workload(struct perf_evlist *evlist,
+				  struct perf_record_opts *opts,
+				  const char *argv[])
+{
+	int child_ready_pipe[2], go_pipe[2];
+	char bf;
+
+	if (pipe(child_ready_pipe) < 0) {
+		perror("failed to create 'ready' pipe");
+		return -1;
+	}
+
+	if (pipe(go_pipe) < 0) {
+		perror("failed to create 'go' pipe");
+		goto out_close_ready_pipe;
+	}
+
+	evlist->workload.pid = fork();
+	if (evlist->workload.pid < 0) {
+		perror("failed to fork");
+		goto out_close_pipes;
+	}
+
+	if (!evlist->workload.pid) {
+		if (opts->pipe_output)
+			dup2(2, 1);
+
+		close(child_ready_pipe[0]);
+		close(go_pipe[1]);
+		fcntl(go_pipe[0], F_SETFD, FD_CLOEXEC);
+
+		/*
+		 * Do a dummy execvp to get the PLT entry resolved,
+		 * so we avoid the resolver overhead on the real
+		 * execvp call.
+		 */
+		execvp("", (char **)argv);
+
+		/*
+		 * Tell the parent we're ready to go
+		 */
+		close(child_ready_pipe[1]);
+
+		/*
+		 * Wait until the parent tells us to go.
+		 */
+		if (read(go_pipe[0], &bf, 1) == -1)
+			perror("unable to read pipe");
+
+		execvp(argv[0], (char **)argv);
+
+		perror(argv[0]);
+		kill(getppid(), SIGUSR1);
+		exit(-1);
+	}
+
+	if (!opts->system_wide && opts->target_tid == -1 && opts->target_pid == -1)
+		evlist->threads->map[0] = evlist->workload.pid;
+
+	close(child_ready_pipe[1]);
+	close(go_pipe[0]);
+	/*
+	 * wait for child to settle
+	 */
+	if (read(child_ready_pipe[0], &bf, 1) == -1) {
+		perror("unable to read pipe");
+		goto out_close_pipes;
+	}
+
+	evlist->workload.cork_fd = go_pipe[1];
+	close(child_ready_pipe[0]);
+	return 0;
+
+out_close_pipes:
+	close(go_pipe[0]);
+	close(go_pipe[1]);
+out_close_ready_pipe:
+	close(child_ready_pipe[0]);
+	close(child_ready_pipe[1]);
+	return -1;
+}
+
+int perf_evlist__start_workload(struct perf_evlist *evlist)
+{
+	if (evlist->workload.cork_fd > 0) {
+		/*
+		 * Remove the cork, let it rip!
+		 */
+		return close(evlist->workload.cork_fd);
+	}
+
+	return 0;
+}
diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
index 231c06f8286b..07d56b3e6d61 100644
--- a/tools/perf/util/evlist.h
+++ b/tools/perf/util/evlist.h
@@ -6,6 +6,7 @@
 #include "../perf.h"
 #include "event.h"
 #include "util.h"
+#include <unistd.h>
 
 struct pollfd;
 struct thread_map;
@@ -22,6 +23,10 @@ struct perf_evlist {
 	int		 nr_fds;
 	int		 nr_mmaps;
 	int		 mmap_len;
+	struct {
+		int	cork_fd;
+		pid_t	pid;
+	} workload;
 	bool		 overwrite;
 	union perf_event event_copy;
 	struct perf_mmap *mmap;
@@ -68,6 +73,11 @@ int perf_evlist__open(struct perf_evlist *evlist, bool group);
 void perf_evlist__config_attrs(struct perf_evlist *evlist,
 			       struct perf_record_opts *opts);
 
+int perf_evlist__prepare_workload(struct perf_evlist *evlist,
+				  struct perf_record_opts *opts,
+				  const char *argv[]);
+int perf_evlist__start_workload(struct perf_evlist *evlist);
+
 int perf_evlist__alloc_mmap(struct perf_evlist *evlist);
 int perf_evlist__mmap(struct perf_evlist *evlist, int pages, bool overwrite);
 void perf_evlist__munmap(struct perf_evlist *evlist);