use C shim to start Android app

This should avoid relying on features of the Android builtin shell,
and so hopefully avoid failures like this one
http://git-annex.branchable.com/design/assistant/blog/day_197__template_haskell/#comment-07f90830f78f6495dcbdf90eb8636129

The C shim sets up busybox, and uses its builtin shell to run runshell.

It's important that busybox be configured with
CONFIG_FEATURE_SH_STANDALONE, so that while runshell is running, it
does not rely on either system utilities, or busybox being already
installed.

standalone/android/.gitignore

@@ -1 +1,2 @@
 build-utils
+start

standalone/android/Makefile

@@ -12,7 +12,7 @@ export ANDROID_NDK_ROOT=$(HOME)/tmp/android-ndk-r8d
 
 GITTREE=source/git/installed-tree
 
-build: source build-utils
+build: source build-utils start
 	# Debug build because it does not need signing keys.
 	cd source/term && tools/build-debug
 
@@ -30,6 +30,7 @@ build: source build-utils
 	cp source/git/git-upload-pack source/term/libs/armeabi/lib.git-upload-pack.so
 	arm-linux-androideabi-strip --strip-unneeded --remove-section=.comment --remove-section=.note source/term/libs/armeabi/*
 	cp runshell source/term/libs/armeabi/lib.runshell.so
+	cp start source/term/libs/armeabi/lib.start.so
 	
 	# remove git stuff we don't need to save space
 	rm -rf $(GITTREE)/bin/git-cvsserver \
@@ -117,7 +118,8 @@ source:
 	git clone git://github.com/jackpal/Android-Terminal-Emulator.git source/term
 
 clean:
-	rm -rf $(GITTREE) build-utils
+	rm -rf $(GITTREE)
+	rm -f build-utils start
 	cd source/busybox && $(MAKE) clean
 	#cd source/openssl && $(MAKE) clean
 	cd source/openssh && $(MAKE) clean

standalone/android/busybox_config

@@ -966,9 +966,9 @@ CONFIG_CTTYHACK=y
 # CONFIG_HUSH_EXPORT_N is not set
 # CONFIG_HUSH_MODE_X is not set
 # CONFIG_MSH is not set
-# CONFIG_FEATURE_SH_IS_ASH is not set
+CONFIG_FEATURE_SH_IS_ASH=y
 # CONFIG_FEATURE_SH_IS_HUSH is not set
-CONFIG_FEATURE_SH_IS_NONE=y
+# CONFIG_FEATURE_SH_IS_NONE is not set
 # CONFIG_FEATURE_BASH_IS_ASH is not set
 # CONFIG_FEATURE_BASH_IS_HUSH is not set
 CONFIG_FEATURE_BASH_IS_NONE=y

standalone/android/runshell

@@ -1,13 +1,10 @@
 #!/system/bin/sh
-# This is run by the Android app, and runs a shell in an environment
-# configured for git-annex.
+# This is runs a shell in an environment configured for git-annex.
 
 set -e
 
 prep () {
-	# I'm installed as lib/lib.runshell.so
-	orig="$(pwd)"
-	cd "$0/../.."
+	# lib.start.so will run us in the root of our app directory
 	base="$(pwd)"
 
 	# Cannot rely on Android providing a sane HOME
@@ -57,7 +54,7 @@ buildtree () {
 }
 
 install () {
-	if [ ! -d "$base/bin" ]; then
+	if [ ! -e "$base/git-annex" ]; then
 		if ! mkdir -p "$HOME"; then
 			echo "mkdir of $HOME failed!"
 		fi

standalone/android/start.c

@@ -0,0 +1,52 @@
+/* Installed as lib.start.so, this bootstraps a working busybox and uses
+ * it to run lib.runshell.so. */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+void chopdir (char *s) {
+	char *p=strrchr(s, '/');
+	if (p == NULL) {
+		fprintf(stderr, "cannot find directory in %s", s);
+		exit(1);
+	}
+	p[0] = '\0';
+}
+
+main () {
+	char buf[1024];
+	char *p;
+	struct stat st_buf;
+
+	/* Get something like /data/data/ga.androidterm/lib/lib.start.so */
+	int n=readlink("/proc/self/exe", buf, 1023);
+	if (n < 1) {
+		fprintf(stderr, "failed to find own name");
+		exit(1);
+	}
+	buf[n] = '\0';
+
+	/* Change directory to something like /data/data/ga.androidterm */
+	chopdir(buf);
+	chopdir(buf);
+	if (chdir(buf) != 0) {
+		perror("chdir");
+		exit(1);
+	}
+
+	/* If this is the first run, set up busybox link. */
+	if (stat("bin/busybox", &st_buf) != 0) {
+		mkdir("bin", 0777);
+		if (link("lib/lib.busybox.so", "bin/busybox") != 0) {
+			perror("link busybox");
+			exit(1);
+		}
+	}
+
+	execl("bin/busybox", "bin/busybox", "sh", "lib/lib.runshell.so", NULL);
+	perror("error running busybox sh");
+}

standalone/android/term.patch

@@ -37,7 +37,7 @@ index f6952f0..4b2aa5f 100644
          String execPath = LaunchActivity.getDataDir(this) + "/bin/execpty";
          ProcessBuilder execBuild =
 -                new ProcessBuilder(execPath, "/system/bin/sh", "-");
-+                new ProcessBuilder(execPath, "/data/data/ga.androidterm/lib/lib.runshell.so", "");
++                new ProcessBuilder(execPath, "/data/data/ga.androidterm/lib/lib.start.so", "");
          execBuild.redirectErrorStream(true);
          Process exec = null;
          try {
@@ -50,7 +50,7 @@ index 67287b2..1f9afa1 100644
     <string name="pref_ime_default">0</string>
     <bool name="pref_alt_sends_esc_default">false</bool>
 -   <string name="pref_shell_default">/system/bin/sh -</string>
-+   <string name="pref_shell_default">/data/data/ga.androidterm/lib/lib.runshell.so</string>
++   <string name="pref_shell_default">/data/data/ga.androidterm/lib/lib.start.so</string>
     <string name="pref_initialcommand_default"></string>
     <string name="pref_termtype_default">screen</string>
 -   <bool name="pref_close_window_on_process_exit_default">true</bool>