profiling: add streaming-write profiling helper

Writes 1GB of zeros to a gocryptfs mount while collecting
cpu and memory profiles.

profiling/streaming-write.bash

@@ -0,0 +1,22 @@
+#!/bin/bash -eu
+
+cd "$(dirname "$0")"
+
+T=$(mktemp -d)
+mkdir $T/a $T/b
+
+../gocryptfs -init -quiet -scryptn 10 -extpass "echo test" $T/a
+../gocryptfs -quiet -extpass "echo test" -cpuprofile $T/cprof -memprofile $T/mprof \
+	$T/a $T/b
+
+# Cleanup trap
+trap "cd /; fusermount -u -z $T/b; rm -Rf $T/a" EXIT
+
+# Write 10 x 100MB instead of 1 x 1GB to keep the used disk space low
+for i in $(seq 1 10); do
+	dd if=/dev/zero of=$T/b/zero bs=1M count=100
+done
+
+echo
+echo "Hint: go tool pprof ../gocryptfs $T/cprof"
+echo "      go tool pprof -alloc_space ../gocryptfs /tmp/tmp.DRhBSFO6pu/mprof"