移植exFAT到Android4.2.2
最近在Android上测试64GB的TF卡支持情况，发现在Windows平台上默认会把卡格式化为exFAT，而不是以前的FAT32或NTFS，故而引发了我对该文件系统的了解。本文是在RK3188 Android4.2上面进行移植实验并验证通过的。
方法/步骤
最近在Android上测试64GB的TF卡支持情况，发现在Windows平台上默认会把卡格式化为exFAT，而不是以前的FAT32或NTFS，故而引发了我对该文件系统的了解。
在Linux内核中不支持exFAT文件系统，需要像对ntfs（移植可查阅“参考网址”相关内容）支持一样使用fuse，即用户态文件系统，那什么是exFAT和fuse呢？
1.exFAT
exFAT（Extended File Allocation Table），又名FAT64，是一种特别适合于闪存的文件系统，可支持单个文件超过4GB的大小。
2.fuse
用户空间文件系统（Filesystem in Userspace，简称FUSE）是操作系统中的概念，指完全在用户态实现的文件系统。目前Linux通过内核模块对此进行支持。
了解完了相关内容，那如何移植呢？下面是移植过程：
1.准备工作
a.exFAT源码
使用svn co http://exfat.googlecode.com/svn/trunk/ exfat-read-only命令下载整份exfat源码到当前的exfat-read-only目录中，现在的（2013年07月24日的版本为1.0.0）。
b.fuse源码
从https://code.google.com/p/exfat/wiki/HOWTO了解到还需要fuse-devel或libfuse-dev，故而从http://sourceforge.net/projects/fuse/files/fuse-2.X/2.9.3/下载最新的fuse-2.9.3.tar.gz文件。
2.移植步骤
a.设置内核的配置：CONFIG_FUSE_FS=y；（会创建/dev/fuse结点）
b.在Android源码目录下的external目录下创建exfat-fuse目录，交将上面通过svn下载的exFAT代码复制到该目录下，并将fuse-2.9.3.tar.gz文件解压后将其文件也复制到该目录下，进入到exfat-fuse目录，执行./configure命令，会创建include/config.h等文件；
c.在exfat-fuse目录下创建Android.mk文件，内容如下：
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
SRCPATH := lib
LOCAL_CFLAGS := -D_FILE_OFFSET_BITS=64 -DFUSE_USE_VERSION=26
LOCAL_MODULE_TAGS := optional
LOCAL_MODULE := libfuse_exfat
LOCAL_SRC_FILES := $(SRCPATH)/buffer.c
LOCAL_SRC_FILES += $(SRCPATH)/cuse_lowlevel.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_kern_chan.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_loop.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_loop_mt.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_lowlevel.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_mt.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_opt.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_session.c
LOCAL_SRC_FILES += $(SRCPATH)/fuse_signals.c
LOCAL_SRC_FILES += $(SRCPATH)/helper.c
LOCAL_SRC_FILES += $(SRCPATH)/mount.c
LOCAL_SRC_FILES += $(SRCPATH)/mount_util.c
LOCAL_SRC_FILES += $(SRCPATH)/ulockmgr.c
LOCAL_SHARED_LIBRARIES := libdl
LOCAL_PRELINK_MODULE := false
LOCAL_C_INCLUDES := $(LOCAL_PATH)/include
include $(BUILD_SHARED_LIBRARY)
include $(CLEAR_VARS)
SRCPATH := libexfat
LOCAL_CFLAGS := -D_FILE_OFFSET_BITS=64 -DFUSE_USE_VERSION=26 -D__GLIBC__=1
LOCAL_MODULE_TAGS := optional
LOCAL_MODULE := libexfat
LOCAL_SRC_FILES := $(SRCPATH)/cluster.c
LOCAL_SRC_FILES += $(SRCPATH)/io.c
LOCAL_SRC_FILES += $(SRCPATH)/log.c
LOCAL_SRC_FILES += $(SRCPATH)/lookup.c
LOCAL_SRC_FILES += $(SRCPATH)/mount.c
LOCAL_SRC_FILES += $(SRCPATH)/node.c
LOCAL_SRC_FILES += $(SRCPATH)/time.c
LOCAL_SRC_FILES += $(SRCPATH)/utf.c
LOCAL_SRC_FILES += $(SRCPATH)/utils.c
LOCAL_SHARED_LIBRARIES := libdl libfuse_exfat
LOCAL_PRELINK_MODULE := false
include $(BUILD_SHARED_LIBRARY)
include $(CLEAR_VARS)
LOCAL_CFLAGS := -D_FILE_OFFSET_BITS=64 -D__GLIBC__=1
LOCAL_C_INCLUDES := $(LOCAL_PATH)/libexfat
LOCAL_MODULE := dumpexfat
LOCAL_MODULE_TAGS := optional
LOCAL_SRC_FILES := dump/main.c
LOCAL_SHARED_LIBRARIES := libexfat
include $(BUILD_EXECUTABLE)
include $(CLEAR_VARS)
LOCAL_CFLAGS := -D_FILE_OFFSET_BITS=64 -D__GLIBC__=1
LOCAL_C_INCLUDES := $(LOCAL_PATH)/libexfat
LOCAL_MODULE := fsck.exfat
LOCAL_MODULE_TAGS := optional
LOCAL_SRC_FILES := fsck/main.c
LOCAL_SHARED_LIBRARIES := libexfat
include $(BUILD_EXECUTABLE)
include $(CLEAR_VARS)
LOCAL_CFLAGS := -D_FILE_OFFSET_BITS=64 -D__GLIBC__=1
LOCAL_C_INCLUDES := $(LOCAL_PATH)/libexfat
LOCAL_MODULE := exfat.label
LOCAL_MODULE_TAGS := optional
LOCAL_SRC_FILES := label/main.c
LOCAL_SHARED_LIBRARIES := libexfat
include $(BUILD_EXECUTABLE)
include $(CLEAR_VARS)
LOCAL_CFLAGS := -D_FILE_OFFSET_BITS=64 -D__GLIBC__=1
LOCAL_C_INCLUDES := $(LOCAL_PATH)/libexfat
LOCAL_MODULE := mkfs.exfat
LOCAL_MODULE_TAGS := optional
LOCAL_SRC_FILES := mkfs/main.c mkfs/cbm.c mkfs/fat.c mkfs/rootdir.c mkfs/uct.c mkfs/vbr.c mkfs/mkexfat.c mkfs/uctc.c
LOCAL_SHARED_LIBRARIES := libexfat
include $(BUILD_EXECUTABLE)
include $(CLEAR_VARS)
LOCAL_CFLAGS := -D_FILE_OFFSET_BITS=64 -DFUSE_USE_VERSION=26 -D__GLIBC__=1
LOCAL_C_INCLUDES := $(LOCAL_PATH)/include $(LOCAL_PATH)/libexfat
LOCAL_MODULE := mount.exfat
LOCAL_MODULE_TAGS := optional
LOCAL_SRC_FILES := fuse/main.c
LOCAL_SHARED_LIBRARIES := libfuse_exfat libexfat
include $(BUILD_EXECUTABLE)
d.在相应产品的device.mk文件里添加如下语句：
PRODUCT_PACKAGES += \
fsck.exfat mount.exfat mkfs.exfat
我们现在只需要上面3个工具即可，而添加的Android.mk里还有其他工具，如果也想编译进来，可直接加到该配置项后面。
e.跟库相关配置添加好了，接下来就是编译和处理编译异常了，刚开始编译，出现如下错误：
target thumb C: libfuse_exfat <= external/exfat-fuse/lib/buffer.c
In file included from external/exfat-fuse/lib/buffer.c:12:0:
external/exfat-fuse/lib/fuse_i.h:35:2: error: unknown type name 'pthread_mutex_t'
external/exfat-fuse/lib/fuse_i.h:82:2: error: unknown type name 'pthread_mutex_t'
external/exfat-fuse/lib/fuse_i.h:84:2: error: unknown type name 'pthread_key_t'
external/exfat-fuse/lib/fuse_i.h:130:23: error: unknown type name 'pthread_t'
external/exfat-fuse/lib/buffer.c: In function 'fuse_buf_write':
external/exfat-fuse/lib/buffer.c:48:35: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c:51:34: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c: In function 'fuse_buf_read':
external/exfat-fuse/lib/buffer.c:82:34: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c:85:33: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c: In function 'fuse_buf_fd_to_fd':
external/exfat-fuse/lib/buffer.c:146:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
external/exfat-fuse/lib/buffer.c: In function 'fuse_buf_splice':
external/exfat-fuse/lib/buffer.c:171:19: error: 'SPLICE_F_MOVE' undeclared (first use in this function)
external/exfat-fuse/lib/buffer.c:171:19: note: each undeclared identifier is reported only once for each function it appears in
external/exfat-fuse/lib/buffer.c:173:19: error: 'SPLICE_F_NONBLOCK' undeclared (first use in this function)
external/exfat-fuse/lib/buffer.c:185:3: warning: implicit declaration of function 'splice' [-Wimplicit-function-declaration]
external/exfat-fuse/lib/buffer.c: In function 'fuse_buf_copy_one':
external/exfat-fuse/lib/buffer.c:232:27: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c:233:27: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c:236:15: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c:236:41: warning: pointer of type 'void *' used in arithmetic [-Wpointer-arith]
external/exfat-fuse/lib/buffer.c: In function 'fuse_buf_copy':
external/exfat-fuse/lib/buffer.c:313:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
看到是跟多线程与splice相关的，从相关资料了解到Android的bionic里面对pthread相关函数支持不佳，故而将相应功能先通过宏屏蔽掉：
a).将./include/config.h文件的#define HAVE_SPLICE 1注释掉；
b).修改./lib/fuse_mt.c文件，在fuse_loop_mt_proc函数中，将res = fuse_session_loop_mt(se);一句使用#ifdef __MULTI_THREAD和#endif括起来；
在同一文件中的fuse_loop_mt函数中，将如下语句也使用上面的宏括起来：
int res = fuse_start_cleanup_thread(f);
if (res)
return -1;
res = fuse_session_loop_mt(fuse_get_session(f));
fuse_stop_cleanup_thread(f);
并在该函数的第一句前加上int res = -1;一句。
修改./lib/cuse_lowlevel.c文件，在cuse_lowlevel_main函数中，将如下语句使用上面的宏括起来：
if (multithreaded)
res = fuse_session_loop_mt(se);
else
修改./lib/fuse.c文件，使用上面的宏将fuse_start_cleanup_thread和fuse_stop_cleanup_thread两函数（包括函数体）括起来；
修改./lib/fuse_loop_mt.c文件，使用上面的宏将整个文件内容括起来；
修改./lib/helper.c文件，在fuse_main_common函数中，将如下语句使用上面的宏括起来：
if (multithreaded)
res = fuse_loop_mt(fuse);
else
c).修改./include/fuse_common.h文件，添加#include <pthread.h>定义。
此时再次编译，有如下提示：
external/exfat-fuse/lib/fuse.c: In function 'fuse_fs_read_buf':
external/exfat-fuse/lib/fuse.c:1804:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
external/exfat-fuse/lib/fuse.c: In function 'mtime_eq':
external/exfat-fuse/lib/fuse.c:2427:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
external/exfat-fuse/lib/fuse.c:2428:3: error: 'struct stat const' has no member named 'st_mtim'
external/exfat-fuse/lib/fuse.c: In function 'update_stat':
external/exfat-fuse/lib/fuse.c:2455:24: error: 'struct stat const' has no member named 'st_mtim'
external/exfat-fuse/lib/fuse.c: In function 'fuse_lib_setattr':
external/exfat-fuse/lib/fuse.c:2810:17: error: 'struct stat' has no member named 'st_atim'
external/exfat-fuse/lib/fuse.c:2815:17: error: 'struct stat' has no member named 'st_mtim'
external/exfat-fuse/lib/fuse.c:2825:20: error: 'struct stat' has no member named 'st_atim'
external/exfat-fuse/lib/fuse.c:2827:20: error: 'struct stat' has no member named 'st_mtim'
没有相应的成员，做如下修改：
a).修改./include/config.h文件，将#define HAVE_STRUCT_STAT_ST_ATIM 1屏蔽掉；
b).修改./lib/fuse.c文件，在fuse_lib_setattr函数中的#ifdef HAVE_UTIMENSAT宏判断里做如下修改：
将tv[0] = attr->st_atim;修改为tv[0].tv_nsec = attr->st_atime;
将tv[1] = attr->st_mtim;修改为tv[1].tv_nsec = attr->st_mtime;
再次编译，出现如下错误：
external/exfat-fuse/lib/mount.c: In function 'exec_fusermount':
external/exfat-fuse/lib/mount.c:142:8: error: 'FUSERMOUNT_DIR' undeclared (first use in this function)
external/exfat-fuse/lib/mount.c:142:8: note: each undeclared identifier is reported only once for each function it appears in
external/exfat-fuse/lib/mount.c:142:23: error: expected ')' before string constant
external/exfat-fuse/lib/mount.c:142:23: error: too few arguments to function 'execv'
修改./lib/mount.c文件，在合适的位置添加如下语句：
#ifndef FUSERMOUNT_DIR
#define FUSERMOUNT_DIR "/system/bin/bin"
#endif
再次编译，出现如下错误：
external/exfat-fuse/lib/mount_util.c: In function 'mtab_needs_update':
external/exfat-fuse/lib/mount_util.c:37:19: error: '_PATH_MOUNTED' undeclared (first use in this function)
external/exfat-fuse/lib/mount_util.c:37:19: note: each undeclared identifier is reported only once for each function it appears in
修改./lib/mount_util.c文件，在合适的位置添加如下语句：
#ifndef _PATH_MOUNTED
#define _PATH_MOUNTED "/etc/mtab"
#endif
再次编译，出现如下错误提示：
/home/guochongxin/rk/3188/new/SDK4.2.2/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.6/bin/../lib/gcc/arm-linux-androideabi/4.6.x-google/../../../../arm-linux-androideabi/bin/ld: error: symbol __fuse_process_cmd has undefined version
/home/guochongxin/rk/3188/new/SDK4.2.2/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.6/bin/../lib/gcc/arm-linux-androideabi/4.6.x-google/../../../../arm-linux-androideabi/bin/ld: error: symbol fuse_lowlevel_new has undefined version FUSE_2.5
/home/guochongxin/rk/3188/new/SDK4.2.2/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.6/bin/../lib/gcc/arm-linux-androideabi/4.6.x-google/../../../../arm-linux-androideabi/bin/ld: error: symbol fuse_chan_new has undefined version FUSE_2.4
/home/guochongxin/rk/3188/new/SDK4.2.2/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.6/bin/../lib/gcc/arm-linux-androideabi/4.6.x-google/../../../../arm-linux-androideabi/bin/ld: error: symbol fuse_teardown has undefined version FUSE_2.2
collect2: ld returned 1 exit status
修改lib/fuse_misc.h文件，将#define FUSE_SYMVER(x) __asm__(x)修改为#define FUSE_SYMVER(x)
再次编译，出现如下错误：
In file included from external/exfat-fuse/libexfat/exfat.h:33:0,
from external/exfat-fuse/libexfat/cluster.c:23:
external/exfat-fuse/libexfat/compiler.h:28:2: error: #error C99-compliant compiler is required
修改./libexfat/compiler.h文件，将如下语句屏蔽掉：
#if __STDC_VERSION__ < 199901L
#error C99-compliant compiler is required
#endif
再次编译，此时编译通过了，那么继续接下来的修改吧。
f.相应的库和工具编译好了，剩下上层来调用了，修改vold相关文件来实现：
a).在Android源码的system/vold目录下添加exFat.h和exFat.cpp文件，相应的源码如下：
exFat.h:
#ifndef _EXFAT_H
#define _EXFAT_H
#include <unistd.h>
class exFat {
public:
static int doMount(const char *fsPath, const char *mountPoint, bool ro, int ownerUid);
static int unMount(const char *mountPoint);
static int format(const char *fsPath, unsigned int numSectors);
};
#endif
exFat.cpp:
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <linux/kdev_t.h>
#define LOG_TAG "Vold"
#include <cutils/log.h>
#include <cutils/properties.h>
#include "exFat.h"
static char EXFAT_PATH[] = "/system/bin/mount.exfat";
extern "C" int logwrap(int argc, const char **argv, int background);
extern "C" int mount(const char *, const char *, const char *, unsigned long, const void *);
int exFat::doMount(const char *fsPath, const char *mountPoint, bool ro, int ownerUid) {
int rc = 0;
do {
if(!ro){
const char *args[3];
args[0] = EXFAT_PATH;
args[1] = fsPath;
args[2] = mountPoint;
rc = logwrap(3, args, 1);
SLOGI(" %s %s %s", EXFAT_PATH, fsPath, mountPoint);
if(!rc){
SLOGI("Mount EXFAT device form %s to %s OK",fsPath,mountPoint);
char *lost_path;
asprintf(&lost_path, "%s/LOST.DIR", mountPoint);
if (access(lost_path, F_OK)) {
/*
* Create a LOST.DIR in the root so we have somewhere to put
* lost cluster chains (fsck_msdos doesn't currently do this)
*/
if (mkdir(lost_path, 0755)) {
SLOGE("Unable to create LOST.DIR (%s)", strerror(errno));
}
}
free(lost_path);
return 0;
}else{
SLOGE("Mount EXFAT device form %s to %s failed",fsPath,mountPoint);
return -1;
}
}else{
const char *args[5];
args[0] = EXFAT_PATH;
args[1] = fsPath;
args[2] = mountPoint;
args[3] = "-o";
args[4] = "ro,uid=1000";
rc = logwrap(5, args, 1);
if(!rc){
SLOGI("Mount EXFAT device form %s to %s OK.(Read-only)",fsPath,mountPoint);
return 0;
}else{
SLOGE("Mount EXFAT device form %s to %s failed.(Read-only)",fsPath,mountPoint);
return -1;
}
}
} while (0);
return rc;
}
int exFat::unMount(const char *mountPoint) {
int rc = 0;
do {
const char *args[3];
args[0] = "umount";
args[1] = mountPoint;
args[2] = NULL;
rc = logwrap(2, args, 1);
if(!rc){
SLOGI("unMount EXFAT device %s OK",mountPoint);
return 0;
}else{
SLOGE("unMount EXFAT device %s failed",mountPoint);
return -1;
}
} while (0);
return rc;
}
int exFat::format(const char *fsPath, unsigned int numSectors) {
return 0;
}
b).修改system/vold/Android.mk文件，在common_src_files量中将exFat.cpp添加进去；
c).修改system/vold/Volume.cpp文件，进行如下修改：
添加#include "exFat.h"一句；
修改int Volume::mountVol()函数中的如下语句：
if (Fat::doMount(devicePath, "/mnt/secure/staging", false, false, false,
AID_SYSTEM, gid, 0702, true)) {
SLOGE("%s failed to mount via VFAT (%s)\n", devicePath, strerror(errno));
continue;
}
为
if (Fat::doMount(devicePath, "/mnt/secure/staging", false, false, false,
AID_SYSTEM, gid, 0702, true)) {
SLOGE("%s failed to mount via VFAT (%s)\n", devicePath, strerror(errno));
if(exFat::doMount(devicePath, "/mnt/secure/staging", false, 1000)){
SLOGE("%s failed to mount via EXFAT (%s)\n", devicePath, strerror(errno));
continue;
}
}
至此，上层也修改好了，继续编译。
g.编译好后烧录运行，Android跑起来后，插入64GB的exFAT文件系统的TF卡，其中logcat信息中有如下错误提示：
I//system/bin/mount.exfat( 118): FUSE exfat 1.0.0
I//system/bin/mount.exfat( 118): ERROR: failed to get size of `/dev/block/vold/179:1'.
该问题从https://groups.google.com/forum/#!msg/exfat/Iei35MqkRGk/UeGSjnbzgQsJ可得知是一个已知问题，主要是fuse-exfat使用的LFS在Android native中没有提供相应的API函数，根据上面的提示，查找到该提示是在exfat-fuse目录中的./libexfat/io.c文件中的exfat_open处理，该函数会调用到exfat_seek，通过其来获得整个文件的大小，但该函数返回小于0的值，继续跟踪，该函数会调用到lseek函数，从http://fred-zone.blogspot.com/2011/02/io-offset.html了解到可通过两种方法处理，我们Android.mk里面包含了第一种方法，但无法处理，现在直接使用第二种方法来处理：
修改exfat-fuse目录里的./libexfat/io.c文件，添加如下内容：
#define lseek lseek64
#define pread pread64
#define pwrite pwrite64
#define fcntl __fcntl64
并将exfat-fuse目录里的所有.c和.h文件中的off_t替换为off64_t，重新编译烧录后，插上64GB的T卡后，有如下提示：
I//system/bin/mount.exfat( 116): FUSE exfat 1.0.0
I//system/bin/mount.exfat( 116): WARN: volume was not unmounted cleanly.
I/Vold ( 116): /system/bin/mount.exfat /dev/block/vold/179:1 /mnt/external_sd
I/Vold ( 116): Mount EXFAT device form /dev/block/vold/179:1 to /mnt/external_sd OK
挂载成功了，测试可以读写卡，但拔掉卡后有如下提示：
I/DEBUG ( 119): becae628 408f0940 [heap]
I/DEBUG ( 119): becae62c 401b81b4 /system/lib/libc.so
I/DEBUG ( 119): becae630 400e3602 /system/lib/libexfat.so
I/DEBUG ( 119): becae634 0001c000
I/DEBUG ( 119): becae638 00000252
I/DEBUG ( 119): becae63c 401b81b4 /system/lib/libc.so
I/DEBUG ( 119): becae640 400e3602 /system/lib/libexfat.so
I/DEBUG ( 119): becae644 4018879c /system/lib/libc.so (__pthread_clone)
I/DEBUG ( 119): #01 becae648 883d068a
I/DEBUG ( 119): becae64c 400e0457 /system/lib/libexfat.so (exfat_bug+82)
I/DEBUG ( 119): #02 becae650 becae66c [stack]
I/DEBUG ( 119): becae654 becae66c [stack]
I/DEBUG ( 119): becae658 04d00000
I/DEBUG ( 119): becae65c 04d00000
I/DEBUG ( 119): becae660 00000000
I/DEBUG ( 119): becae664 400e0095 /system/lib/libexfat.so (exfat_pread+36)
I/DEBUG ( 119): becae668 400e3602 /system/lib/libexfat.so
由此可以看到是libexfat的问题，从打印出来的栈信息，初步判断是exfat_bug涉及到影响，修改./libexfat/exfat.h文件，将如下语句：
void exfat_bug(const char* format, ...) PRINTF NORETURN;
void exfat_error(const char* format, ...) PRINTF;
void exfat_warn(const char* format, ...) PRINTF;
void exfat_debug(const char* format, ...) PRINTF;
替换为
#define exfat_debug(x...)
#define exfat_bug(x...)
#define exfat_warn(x...)
#define exfat_error(x...) exfat_errors++
再次编译，有如下错误提示：
target thumb C: libexfat <= external/exfat-fuse/libexfat/log.c
external/exfat-fuse/libexfat/log.c:34:1: error: expected identifier or '(' before '{' token
external/exfat-fuse/libexfat/log.c:56:6: error: expected '=', ',', ';', 'asm' or '__attribute__' before '++' token
external/exfat-fuse/libexfat/log.c:80:1: error: expected identifier or '(' before '{' token
external/exfat-fuse/libexfat/log.c:101:1: error: expected identifier or '(' before '{' token
修改./libexfat/log.c文件，将#include "exfat.h"屏蔽掉，再次编译，有如下错误提示：
external/exfat-fuse/libexfat/lookup.c: In function 'exfat_split':
external/exfat-fuse/libexfat/lookup.c:225:1: error: control reaches end of non-void function [-Werror=return-type]
cc1: some warnings being treated as errors
修改./libexfat/lookup.c文件，在exfat_split函数最后加上return 0;语句，再次编译，有如下错误提示：
external/exfat-fuse/mkfs/mkexfat.c: In function 'get_position':
external/exfat-fuse/mkfs/mkexfat.c:162:1: error: control reaches end of non-void function [-Werror=return-type]
cc1: some warnings being treated as errors
修改./mkfs/mkexfat.c文件，在get_position函数中最后加上return 0;语句，再次编译，未发现错误，烧录后，插拔TF卡未见明显异常信息。至此，移植告一段落了，待后期使用测试了。