Add misc_writer.

bootloader_message.h currently divides /misc into four segments. The
space between 2K and 16K is reserved for vendor use (e.g. bootloader
persists flags). This CL adds a vendor tool "misc_writer", to allow
writing data to the vendor space in /misc, before getting a dedicated
HAL for accessing /misc partition (b/131775112).

Targets need to explicitly include the module, then invoke the
executable to write data. For example, the following command will write
3-byte data ("0xABCDEF") to offset 4 in vendor space (i.e. 2048 + 4 in
/misc).
$ /vendor/bin/misc_writer --vendor-space-offset 4 --hex-string 0xABCDEF

Bug: 132906936
Test: Run recovery_unit_test on crosshatch.
Test: Call the command via init.hardware.rc on crosshatch. Check that
      the call finishes successfully. Then check the contents written to
      /misc (`dd bs=1 skip=2048 if=/dev/block/sda2 count=32 | xxd`).
Change-Id: I79548fc63fc79b705a0320868690569c3106949f
Merged-In: I79548fc63fc79b705a0320868690569c3106949f
(cherry picked from commit 7ae0169842)

bootloader_message/bootloader_message.cpp

@@ -21,6 +21,7 @@
 #include <string.h>
 
 #include <string>
+#include <string_view>
 #include <vector>
 
 #include <android-base/file.h>
@@ -32,7 +33,17 @@
 using android::fs_mgr::Fstab;
 using android::fs_mgr::ReadDefaultFstab;
 
+static std::string g_misc_device_for_test;
+
+// Exposed for test purpose.
+void SetMiscBlockDeviceForTest(std::string_view misc_device) {
+  g_misc_device_for_test = misc_device;
+}
+
 static std::string get_misc_blk_device(std::string* err) {
+  if (!g_misc_device_for_test.empty()) {
+    return g_misc_device_for_test;
+  }
   Fstab fstab;
   if (!ReadDefaultFstab(&fstab)) {
     *err = "failed to read default fstab";
@@ -228,6 +239,37 @@ bool write_wipe_package(const std::string& package_data, std::string* err) {
                               WIPE_PACKAGE_OFFSET_IN_MISC, err);
 }
 
+static bool OffsetAndSizeInVendorSpace(size_t offset, size_t size) {
+  auto total_size = WIPE_PACKAGE_OFFSET_IN_MISC - VENDOR_SPACE_OFFSET_IN_MISC;
+  return size <= total_size && offset <= total_size - size;
+}
+
+bool ReadMiscPartitionVendorSpace(void* data, size_t size, size_t offset, std::string* err) {
+  if (!OffsetAndSizeInVendorSpace(offset, size)) {
+    *err = android::base::StringPrintf("Out of bound read (offset %zu size %zu)", offset, size);
+    return false;
+  }
+  auto misc_blk_device = get_misc_blk_device(err);
+  if (misc_blk_device.empty()) {
+    return false;
+  }
+  return read_misc_partition(data, size, misc_blk_device, VENDOR_SPACE_OFFSET_IN_MISC + offset,
+                             err);
+}
+
+bool WriteMiscPartitionVendorSpace(const void* data, size_t size, size_t offset, std::string* err) {
+  if (!OffsetAndSizeInVendorSpace(offset, size)) {
+    *err = android::base::StringPrintf("Out of bound write (offset %zu size %zu)", offset, size);
+    return false;
+  }
+  auto misc_blk_device = get_misc_blk_device(err);
+  if (misc_blk_device.empty()) {
+    return false;
+  }
+  return write_misc_partition(data, size, misc_blk_device, VENDOR_SPACE_OFFSET_IN_MISC + offset,
+                              err);
+}
+
 extern "C" bool write_reboot_bootloader(void) {
   std::string err;
   return write_reboot_bootloader(&err);