support "sideload over ADB" mode

Rather than depending on the existence of some place to store a file
that is accessible to users on an an unbootable device (eg, a physical
sdcard, external USB drive, etc.), add support for sideloading
packages sent to the device with adb.

This change adds a "minimal adbd" which supports nothing but receiving
a package over adb (with the "adb sideload" command) and storing it to
a fixed filename in the /tmp ramdisk, from where it can be verified
and sideloaded in the usual way.  This should be leave available even
on locked user-build devices.

The user can select "apply package from ADB" from the recovery menu,
which starts minimal-adb mode (shutting down any real adbd that may be
running).  Once minimal-adb has received a package it exits
(restarting real adbd if appropriate) and then verification and
installation of the received package proceeds.

Change-Id: I6fe13161ca064a98d06fa32104e1f432826582f5
diff --git a/minadbd/utils.h b/minadbd/utils.h
new file mode 100644
index 0000000..f70ecd2
--- /dev/null
+++ b/minadbd/utils.h
@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef _ADB_UTILS_H
+#define _ADB_UTILS_H
+
+/* bounded buffer functions */
+
+/* all these functions are used to append data to a bounded buffer.
+ *
+ * after each operation, the buffer is guaranteed to be zero-terminated,
+ * even in the case of an overflow. they all return the new buffer position
+ * which allows one to use them in succession, only checking for overflows
+ * at the end. For example:
+ *
+ *    BUFF_DECL(temp,p,end,1024);
+ *    char*    p;
+ *
+ *    p = buff_addc(temp, end, '"');
+ *    p = buff_adds(temp, end, string);
+ *    p = buff_addc(temp, end, '"');
+ *
+ *    if (p >= end) {
+ *        overflow detected. note that 'temp' is
+ *        zero-terminated for safety. 
+ *    }
+ *    return strdup(temp);
+ */
+
+/* tries to add a character to the buffer, in case of overflow
+ * this will only write a terminating zero and return buffEnd.
+ */
+char*   buff_addc (char*  buff, char*  buffEnd, int  c);
+
+/* tries to add a string to the buffer */
+char*   buff_adds (char*  buff, char*  buffEnd, const char*  s);
+
+/* tries to add a bytes to the buffer. the input can contain zero bytes,
+ * but a terminating zero will always be appended at the end anyway
+ */
+char*   buff_addb (char*  buff, char*  buffEnd, const void*  data, int  len);
+
+/* tries to add a formatted string to a bounded buffer */
+char*   buff_add  (char*  buff, char*  buffEnd, const char*  format, ... );
+
+/* convenience macro used to define a bounded buffer, as well as
+ * a 'cursor' and 'end' variables all in one go.
+ *
+ * note: this doesn't place an initial terminating zero in the buffer,
+ * you need to use one of the buff_ functions for this. or simply
+ * do _cursor[0] = 0 manually.
+ */
+#define  BUFF_DECL(_buff,_cursor,_end,_size)   \
+    char   _buff[_size], *_cursor=_buff, *_end = _cursor + (_size)
+
+#endif /* _ADB_UTILS_H */