FunctionFS: initial implementation

This is the second version of a patch which demonstrates the possibility
of using adbd (Android Debug Bridge daemon) with a generic FunctionFS gadget
instead of a custom adb usb gadget in the Linux kernel. It contains changes
introduced after Benoit's review - thank you Benoit.

The patch adds a new usb access layer to adbd using FunctionFS. The former
usb access method is still available. The method is chosen at runtime
depending if /dev/usb-ffs/adb/ep0 or /dev/android_adb is accessible.

How to use on the target device:

$ insmod g_ffs.ko idVendor=<vendor ID> iSerialNumber=<some string>
$ mount -t functionfs adb /dev/usb-ffs/adb -o uid=2000,gid=2000
$ ./adbd

This patch requires a patch to bionic which adds <linux/usb_functionfs.h>
which is an exact copy of the relevant file in the linux kernel.

Change-Id: I4b42eb267ffa50fca7a5fba46f388a2f083e8b2d
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
[benoit@android.com: detect at runtime if functionfs is mounted
or fallback using f_adb]
Signed-off-by: Benoit Goby <benoit@android.com>

adb/adb.c

@@ -1025,7 +1025,8 @@ int adb_main(int is_daemon, int server_port)
     if (sscanf(value, "%d", &port) == 1 && port > 0) {
         // listen on TCP port specified by service.adb.tcp.port property
         local_init(port);
-    } else if (access("/dev/android_adb", F_OK) == 0) {
+    } else if (access(USB_ADB_PATH, F_OK) == 0 ||
+               access(USB_FFS_ADB_EP0, F_OK) == 0) {
         // listen on USB
         usb_init();
     } else {

adb/adb.h

@@ -462,6 +462,17 @@ extern int SHELL_EXIT_NOTIFY_FD;
 
 #define CHUNK_SIZE (64*1024)
 
+#if !ADB_HOST
+#define USB_ADB_PATH     "/dev/android_adb"
+
+#define USB_FFS_ADB_PATH  "/dev/usb-ffs/adb/"
+#define USB_FFS_ADB_EP(x) USB_FFS_ADB_PATH#x
+
+#define USB_FFS_ADB_EP0   USB_FFS_ADB_EP(ep0)
+#define USB_FFS_ADB_OUT   USB_FFS_ADB_EP(ep1)
+#define USB_FFS_ADB_IN    USB_FFS_ADB_EP(ep2)
+#endif
+
 int sendfailmsg(int fd, const char *reason);
 int handle_host_request(char *service, transport_type ttype, char* serial, int reply_fd, asocket *s);