cmd/trace: add option to output pprof files

The trace tool can generate some interesting profiles, but it was only
exposing them as svg through the web UI.  This adds command line options
to generate the raw pprof file.

Change-Id: I52e4f909fdca6f65c3616add444e3892783640f4
Reviewed-on: https://go-review.googlesource.com/23324
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/trace/main.go

@@ -15,6 +15,14 @@ Generate a trace file with 'go test':
 	go test -trace trace.out pkg
 View the trace in a web browser:
 	go tool trace trace.out
+Generate a pprof-like profile from the trace:
+	go tool trace -pprof=TYPE trace.out > TYPE.pprof
+
+Supported profile types are:
+	- net: network blocking profile
+	- sync: synchronization blocking profile
+	- syscall: syscall blocking profile
+	- sched: scheduler latency profile
 */
 package main
 
@@ -25,6 +33,7 @@ import (
 	"fmt"
 	"html/template"
 	"internal/trace"
+	"io"
 	"log"
 	"net"
 	"net/http"
@@ -39,15 +48,27 @@ Given a trace file produced by 'go test':
 
 Open a web browser displaying trace:
 	go tool trace [flags] [pkg.test] trace.out
+
+Generate a pprof-like profile from the trace:
+    go tool trace -pprof=TYPE [pkg.test] trace.out
+
 [pkg.test] argument is required for traces produced by Go 1.6 and below.
 Go 1.7 does not require the binary argument.
 
+Supported profile types are:
+    - net: network blocking profile
+    - sync: synchronization blocking profile
+    - syscall: syscall blocking profile
+    - sched: scheduler latency profile
+
 Flags:
 	-http=addr: HTTP service address (e.g., ':6060')
+	-pprof=type: print a pprof-like profile instead
 `
 
 var (
-	httpFlag = flag.String("http", "localhost:0", "HTTP service address (e.g., ':6060')")
+	httpFlag  = flag.String("http", "localhost:0", "HTTP service address (e.g., ':6060')")
+	pprofFlag = flag.String("pprof", "", "print a pprof-like profile instead")
 
 	// The binary file name, left here for serveSVGProfile.
 	programBinary string
@@ -73,6 +94,27 @@ func main() {
 		flag.Usage()
 	}
 
+	var pprofFunc func(io.Writer) error
+	switch *pprofFlag {
+	case "net":
+		pprofFunc = pprofIO
+	case "sync":
+		pprofFunc = pprofBlock
+	case "syscall":
+		pprofFunc = pprofSyscall
+	case "sched":
+		pprofFunc = pprofSched
+	}
+	if pprofFunc != nil {
+		if err := pprofFunc(os.Stdout); err != nil {
+			dief("failed to generate pprof: %v\n", err)
+		}
+		os.Exit(0)
+	}
+	if *pprofFlag != "" {
+		dief("unknown pprof type %s\n", *pprofFlag)
+	}
+
 	ln, err := net.Listen("tcp", *httpFlag)
 	if err != nil {
 		dief("failed to create server socket: %v\n", err)