updater: Allow devices to suppress BLKDISCARD

* On some devices TRIM is disabled for security reasons. Don't fail
  flashing the ROM because discard isn't possible in this case.

Change-Id: I044619c3e0b01a496d967ef136501d0190240ad4

updater/Android.mk

@@ -74,6 +74,10 @@ LOCAL_CFLAGS := \
     -Wall \
     -Werror
 
+ifeq ($(BOARD_SUPPRESS_EMMC_WIPE),true)
+    LOCAL_CFLAGS += -DSUPPRESS_EMMC_WIPE
+endif
+
 LOCAL_EXPORT_C_INCLUDE_DIRS := \
     $(LOCAL_PATH)/include
 

updater/blockimg.cpp

@@ -1499,10 +1499,12 @@ static int PerformCommandErase(CommandParameters& params) {
       // length in bytes
       blocks[1] = (range.second - range.first) * static_cast<uint64_t>(BLOCKSIZE);
 
+#ifndef SUPPRESS_EMMC_WIPE
       if (ioctl(params.fd, BLKDISCARD, &blocks) == -1) {
         PLOG(ERROR) << "BLKDISCARD ioctl failed";
         return -1;
       }
+#endif
     }
   }