MTP add/remove storage instead of disabling MTP
Implement a pipe between TWRP and MTP to allow TWRP to tell MTP
to remove storage partitions as they become unavailable (e.g.
during a wipe, unmount, etc) instead of disabling MTP completely.
This includes some fixes and improvements in destructors to
properly remove / delete various items. This also means that we
will not be toggling adb off and on quite as often.
I do not like that we had to add another thread, but we were
unable to use select() on the mtp_usb character device because
this device does not support polling. Select always returned
indicating that the mtp file descriptor was ready to be read and
the resulting read would block. The read block prevented us from
being able to include reading of the pipe between TWRP and MTP in
the main MTP thread.
We might want to add a return pipe letting TWRP know if the
removal of the storage device was successful, but I am not sure
how we want to implement this. It would invovle timeouts in both
TWRP and MTP to ensure that we returned a failure indicator in a
timely manner to TWRP and prevent deleting the storage device in
the case of a failure. Right now we make no attempt to ensure that
an MTP operation is underway like a large file transfer, but we
were not doing anything like this in the past. In some respects we
have limited control over what happens. If the user installs a
zip that unmounts a storage partition, we will not know about the
change in storage status anyway. Regular Android does not have
these troubles because partitions rarely get unmounted like in
recovery. At some point, we have to hold the user accountable for
performing actions that may remove a storage partition while they
are using MTP anyway.
Ideally we do not want to toggle the USB IDs and thus toggle adb
off and on during early boot, but I am not sure what the best way
to handle that at this time.
Change-Id: I9343e5396bf6023d3b994de1bf01ed91d129bc14
diff --git a/mtp/tw_sys_atomics.h b/mtp/tw_sys_atomics.h
new file mode 100644
index 0000000..6349a93
--- /dev/null
+++ b/mtp/tw_sys_atomics.h
@@ -0,0 +1,67 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+#ifndef _TW_SYS_ATOMICS_H
+#define _TW_SYS_ATOMICS_H
+
+#include <sys/cdefs.h>
+#include <sys/time.h>
+
+__BEGIN_DECLS
+
+/* Note: atomic operations that were exported by the C library didn't
+ * provide any memory barriers, which created potential issues on
+ * multi-core devices. We now define them as inlined calls to
+ * GCC sync builtins, which always provide a full barrier.
+ *
+ * NOTE: The C library still exports atomic functions by the same
+ * name to ensure ABI stability for existing NDK machine code.
+ *
+ * If you are an NDK developer, we encourage you to rebuild your
+ * unmodified sources against this header as soon as possible.
+ */
+
+/* This was kanged from Android 4.4 bionic/libc/include/sys/atomics.h
+ * This header was removed in Android 5.0 in favor of stdatomics.h but
+ * to maintain compatibility across multiple trees, we are including our
+ * own copy.
+ */
+
+#ifndef __ATOMIC_INLINE__
+#define __ATOMIC_INLINE__ static __inline__ __attribute__((always_inline))
+#endif
+
+__ATOMIC_INLINE__ int
+__tw_atomic_cmpxchg(int old_value, int new_value, volatile int* ptr)
+{
+ /* We must return 0 on success */
+ return __sync_val_compare_and_swap(ptr, old_value, new_value) != old_value;
+}
+
+__END_DECLS
+
+#endif /* _TW_SYS_ATOMICS_H */