Retry adjusting the size computation for reserved blocks.

Due to the change in https://lwn.net/Articles/546473/, kernel reserves a
few extra blocks (lesser of 2% and 4096 blocks) on ext4 FS which leads to
OTA update failures. Adjust the size computation if the device has
BOARD_HAS_EXT4_RESERVED_BLOCKS := true.

It amends the last attemp in [1]. Now it computes the used blocks from the
make_ext4fs output, instead of altering its argument.

[1]: commit efbb5d2e692283be32069e808b88522727c7fe98.

Bug: 21522719
Bug: 22023465
Bug: 22174684
Change-Id: I9783a51abe6581ff5c75db81e78ac606d0f32c4c
diff --git a/core/Makefile b/core/Makefile
index b1f9484..598b620 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -733,6 +733,7 @@
 $(if $(BOARD_SYSTEMIMAGE_PARTITION_SIZE),$(hide) echo "system_size=$(BOARD_SYSTEMIMAGE_PARTITION_SIZE)" >> $(1))
 $(if $(BOARD_SYSTEMIMAGE_FILE_SYSTEM_TYPE),$(hide) echo "system_fs_type=$(BOARD_SYSTEMIMAGE_FILE_SYSTEM_TYPE)" >> $(1))
 $(if $(BOARD_SYSTEMIMAGE_JOURNAL_SIZE),$(hide) echo "system_journal_size=$(BOARD_SYSTEMIMAGE_JOURNAL_SIZE)" >> $(1))
+$(if $(BOARD_HAS_EXT4_RESERVED_BLOCKS),$(hide) echo "has_ext4_reserved_blocks=$(BOARD_HAS_EXT4_RESERVED_BLOCKS)" >> $(1))
 $(if $(BOARD_SYSTEMIMAGE_SQUASHFS_COMPRESSOR),$(hide) echo "system_squashfs_compressor=$(BOARD_SYSTEMIMAGE_SQUASHFS_COMPRESSOR)" >> $(1))
 $(if $(BOARD_SYSTEMIMAGE_SQUASHFS_COMPRESSOR_OPT),$(hide) echo "system_squashfs_compressor_opt=$(BOARD_SYSTEMIMAGE_SQUASHFS_COMPRESSOR_OPT)" >> $(1))
 $(if $(BOARD_USERDATAIMAGE_FILE_SYSTEM_TYPE),$(hide) echo "userdata_fs_type=$(BOARD_USERDATAIMAGE_FILE_SYSTEM_TYPE)" >> $(1))
@@ -997,7 +998,15 @@
       $(TARGET_OUT) $(systemimage_intermediates)/system_image_info.txt $(1) \
       || ( echo "Out of space? the tree size of $(TARGET_OUT) is (MB): " 1>&2 ;\
            du -sm $(TARGET_OUT) 1>&2;\
-           echo "The max is $$(( $(BOARD_SYSTEMIMAGE_PARTITION_SIZE) / 1048576 )) MB." 1>&2 ;\
+           if [ "$(INTERNAL_USERIMAGES_EXT_VARIANT)" == "ext4" ]; then \
+               maxsize=$(BOARD_SYSTEMIMAGE_PARTITION_SIZE); \
+               if [ "$(BOARD_HAS_EXT4_RESERVED_BLOCKS)" == "true" ]; then \
+                   maxsize=$$((maxsize - 4096 * 4096)); \
+               fi; \
+               echo "The max is $$(( maxsize / 1048576 )) MB." 1>&2 ;\
+           else \
+               echo "The max is $$(( $(BOARD_SYSTEMIMAGE_PARTITION_SIZE) / 1048576 )) MB." 1>&2 ;\
+           fi; \
            mkdir -p $(DIST_DIR); cp $(INSTALLED_FILES_FILE) $(DIST_DIR)/installed-files-rescued.txt; \
            exit 1 )
 endef
@@ -1480,6 +1489,9 @@
 ifdef BOARD_RECOVERYIMAGE_PARTITION_SIZE
 	$(hide) echo "recovery_size=$(BOARD_RECOVERYIMAGE_PARTITION_SIZE)" >> $(zip_root)/META/misc_info.txt
 endif
+ifdef BOARD_HAS_EXT4_RESERVED_BLOCKS
+	$(hide) echo "has_ext4_reserved_blocks=$(BOARD_HAS_EXT4_RESERVED_BLOCKS)" >> $(zip_root)/META/misc_info.txt
+endif
 ifdef TARGET_RECOVERY_FSTYPE_MOUNT_OPTIONS
 	@# TARGET_RECOVERY_FSTYPE_MOUNT_OPTIONS can be empty to indicate that nothing but defaults should be used.
 	$(hide) echo "recovery_mount_options=$(TARGET_RECOVERY_FSTYPE_MOUNT_OPTIONS)" >> $(zip_root)/META/misc_info.txt