Android(安卓)4.4.2 exfat 移植
16lz
2022-04-28
简介
Android原生的平台不支持NTFS和exFAT格式的文件系统，但是Linux已经有相应的开源代码，因此只需找到相应的源码将其移植到Android上即可。
我目前使用的系统是Android 4.4.2的，系统里已经集成了对NTFS文件系统的支持。所以我现在要做的就是将exFAT格式的文件系统移植过来。
基本概念
exFAT（Extended File Allocation Table），又名FAT64，是一种能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。
FUSE 用户空间文件系统（Filesystem in Userppace）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。
上面是基于FUSE做的exFAT文件系统的支持，还有一种是exfat-nofuse的模式，由于时间原因没有去实践了，等以后有机会再去尝试下。感兴趣的同学可以自行去研究下看可不可行。
风骚实战
第一步：下载exFAT相关代码并将exFAT源码导入external目录下并编译通过
我这里是使用别人开源的在Android平台上的源码，exfat有官方源码，但是要在Android平台上编译通过还需要修改若干文件，这里我就取巧了，直接用别人整理好的。代码下载,我现在下载的版本。但是这个源码下载下来还是有编译错误。我做的调整如下：
增加 external/exfat/Android.mk
LOCAL_PATH := $(call my-dir)include \ $(LOCAL_PATH)/fuse/Android.mk \ $(LOCAL_PATH)/exfat/Android.mk \修改 external/exfat/fuse/Android.mk
LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_CFLAGS := -O2 -g -W -Wall -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -DHAVE_CONFIG_H -DFUSE_USE_VERSION=26LOCAL_SRC_FILES := \ buffer.c \ cuse_lowlevel.c \ fuse.c \ fuse_kern_chan.c \ fuse_loop.c \ fuse_loop_mt.c \ fuse_lowlevel.c \ fuse_mt.c fuse_opt.c \ fuse_session.c \ fuse_signals.c \ helper.c \ mount.c \ mount_util.c \ ulockmgr.cLOCAL_C_INCLUDES := \ $(LOCAL_PATH)/includeLOCAL_SYSTEM_SHARED_LIBRARIES:= libc libcutilsLOCAL_LDFLAGS += -ldlLOCAL_MODULE := libfuse-exfatLOCAL_MODULE_TAGS := optionalinclude $(BUILD_STATIC_LIBRARY)修改 external/exfat/exfat/Android.mk
EXFAT_ROOT := $(call my-dir)LOCAL_PATH := $(call my-dir)LINKS := fsck.exfat mkfs.exfatinclude $(CLEAR_VARS)EXFAT_CFLAGS := -O2 -g -W -Wall -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -DHAVE_CONFIG_H \ -Wall -O2 -std=c99 \ -D__GLIBC__ \ -D_FILE_OFFSET_BITS=64 \ -DALWAYS_USE_SYNC_OPTION=1 \ -DUSE_TRANSITIONAL_LFS=1 \ -I$(EXFAT_ROOT)/libexfat \ -I$(EXFAT_ROOT)/../fuse/includeLOCAL_MODULE := mount.exfatLOCAL_SRC_FILES := main.cLOCAL_STATIC_LIBRARIES += libexfat_mount libexfat_fsck libexfat_mkfs libexfat_dump libexfat_labelLOCAL_STATIC_LIBRARIES += libexfat libfuse-exfatLOCAL_LDFLAGS += -ldlinclude $(BUILD_EXECUTABLE)SYMLINKS := $(addprefix $(TARGET_OUT)/bin/,$(LINKS))$(SYMLINKS): EXFAT_BINARY := $(LOCAL_MODULE)$(SYMLINKS): $(LOCAL_INSTALLED_MODULE) $(LOCAL_PATH)/Android.mk @echo "Symlink: $@ -> $(EXFAT_BINARY)" @mkdir -p $(dir $@) @rm -rf $@ $(hide) ln -sf $(EXFAT_BINARY) $@ALL_DEFAULT_INSTALLED_MODULES += $(SYMLINKS)include $(EXFAT_ROOT)/libexfat/Android.mkinclude $(EXFAT_ROOT)/fuse/Android.mkinclude $(EXFAT_ROOT)/mkfs/Android.mkinclude $(EXFAT_ROOT)/fsck/Android.mkinclude $(EXFAT_ROOT)/dump/Android.mkinclude $(EXFAT_ROOT)/label/Android.mk将上面三个Android.mk文件修改好后，就可以编译通过啦。同时它会生成fsck.exfat、mkfs.exfat和 mount.exfat三个可执行bin文件。fsck.exfat用于检测文件系统格式是否是exFAT，mkfs.exfat将文件系统格式化，mount.exfat将exFAT文件系统挂载起来。将生成的bin文件push到Android设备中，直接执行mount.exfat devicePath mountPoint，将exFat文件格式的系统挂载到Android 对应的可访问目录下。这样就可以访问exFat文件格式的U盘了。这一步是为了测试我们的exfat源码是否可以识别和挂载exFAT格式的U盘。测试通过我们就可以执行第二步，实现exFAT格式的U盘自动挂载。
第二步：实现拔插exFAT文件格式的U盘自动挂载
要想实现U盘自动挂载，需要修改system/vold/Volume.cpp文件。因为我的系统已经实现了NTFS文件系统的自动挂载，所以我只要依葫芦画瓢就好了。
首先，在system/vold/目录下，添加Exfat.h和Exfat.cpp文件，代码如下：
Exfat.h
#ifndef _EXFAT_H#define _EXFAT_H#include class Exfat {public: static int check(const char *fsPath); static int doMount(const char *fsPath, const char *mountPoint, bool ro, bool remount, bool executable, int ownerUid, int ownerGid, int permMask, bool createLost);};#endif Exfat.cpp
#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define LOG_TAG "Vold"#include #include #include #include "Exfat.h"#include "VoldUtil.h"static char EXFAT_FIX_PATH[] = "/system/bin/fsck.exfat";static char EXFAT_MOUNT_PATH[] = "/system/bin/mount.exfat";int Exfat::check(const char *fsPath) { if (access(EXFAT_FIX_PATH, X_OK)) { SLOGW("Skipping fs checks\n"); return 0; } int rc = 0; int status; const char *args[4]; /* we first use -n to do ntfs detection */ args[0] = EXFAT_FIX_PATH; args[1] = fsPath; args[2] = NULL; rc = android_fork_execvp(ARRAY_SIZE(args), (char **)args, &status, false, true); if (rc) { errno = ENODATA; return -1; } if (!WIFEXITED(status)) { errno = ENODATA; return -1; } status = WEXITSTATUS(status); switch(status) { case 0: SLOGI("ExFat filesystem check completed OK"); break; default: SLOGE("Filesystem check failed (unknown exit code %d)", status); errno = EIO; return -1; } return 0;}int Exfat::doMount(const char *fsPath, const char *mountPoint, bool ro, bool remount, bool executable, int ownerUid, int ownerGid, int permMask, bool createLost) { int rc; int status; char mountData[255]; const char *args[6]; /* * Note: This is a temporary hack. If the sampling profiler is enabled, * we make the SD card world-writable so any process can write snapshots. * * TODO: Remove this code once we have a drop box in system_server. */ char value[PROPERTY_VALUE_MAX]; property_get("persist.sampling_profiler", value, ""); if (value[0] == '1') { SLOGW("The SD card is world-writable because the" " 'persist.sampling_profiler' system property is set to '1'."); permMask = 0; } sprintf(mountData, "utf8,uid=%d,gid=%d,fmask=%o,dmask=%o," "shortname=mixed,nodev,nosuid,dirsync", ownerUid, ownerGid, permMask, permMask); if (!executable) strcat(mountData, ",noexec"); if (ro) strcat(mountData, ",ro"); if (remount) strcat(mountData, ",remount"); SLOGD("Mounting ntfs with options:%s\n", mountData); args[0] = EXFAT_MOUNT_PATH; args[1] = "-o"; args[2] = mountData; args[3] = fsPath; args[4] = mountPoint; args[5] = NULL; rc = android_fork_execvp(ARRAY_SIZE(args), (char **)args, &status, false, true); if (rc && errno == EROFS) { SLOGE("%s appears to be a read only filesystem - retrying mount RO", fsPath); strcat(mountData, ",ro"); rc = android_fork_execvp(ARRAY_SIZE(args), (char **)args, &status, false, true); } if (!WIFEXITED(status)) { return rc; } if (rc == 0 && createLost) { 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 rc;} 然后，在Android.mk中加入Exfat.cpp
common_src_files := \ ... Ntfs.cpp \ Exfat.cpp \ ...最后，在Volume.cpp中加入相应的代码
...#include "Exfat.h"...int Volume::mountVol() { ... for (i = 0; i < n; i++) { ... int ntfs = 0; int exfat = 0; //add by steven if (Fat::check(devicePath)) { if (errno == ENODATA) { SLOGW("%s does not contain a FAT filesystem\n", devicePath); if (Fat::doMount(devicePath, getMountpoint(), false, false, false, AID_MEDIA_RW, AID_MEDIA_RW, 0002, true)) { /* try the NTFS filesystem */ if (!Ntfs::check(devicePath)) { ntfs = 1; SLOGI("%s contain a NTFS filesystem\n", devicePath); goto mnt; } /* try the EXFAT filesystem */ else if (!Exfat::check(devicePath)) { //add by steven exfat = 1; SLOGI("%s contain a EXFAT filesystem\n", devicePath); goto mnt; } else { if (Extfs::doMount(devicePath, getMountpoint(), false, false, AID_MEDIA_RW, AID_MEDIA_RW, 0002)) { SLOGE("%s failed to mount via EXTFS (%s)\n", devicePath, strerror(errno)); continue; } else { goto mounted; } } } else { goto mounted; } } errno = EIO; /* Badness - abort the mount */ SLOGE("%s failed FS checks (%s)", devicePath, strerror(errno)); setState(Volume::State_Idle); return -1; }mnt: errno = 0; int gid; if (ntfs) { if (Ntfs::doMount(devicePath, getMountpoint(), false, false, false, AID_MEDIA_RW, AID_MEDIA_RW, 0002, true)) { SLOGE("%s failed to mount via NTFS (%s)\n", devicePath, strerror(errno)); continue; } } else if (exfat) { //add by steven if (Exfat::doMount(devicePath, getMountpoint(), false, false, false, AID_MEDIA_RW, AID_MEDIA_RW, 0002, true)) { SLOGE("%s failed to mount via Exfat (%s)\n", devicePath, strerror(errno)); continue; } } else if (Fat::doMount(devicePath, getMountpoint(), false, false, false, AID_MEDIA_RW, AID_MEDIA_RW, 0002, true)) { SLOGE("%s failed to mount via VFAT (%s)\n", devicePath, strerror(errno)); continue; }mounted: extractMetadata(devicePath); if (providesAsec && mountAsecExternal() != 0) { SLOGE("Failed to mount secure area (%s)", strerror(errno)); umount(getMountpoint()); setState(Volume::State_Idle); return -1; } char service[64]; snprintf(service, 64, "fuse_%s", getLabel()); property_set("ctl.start", service); setState(Volume::State_Mounted); mCurrentlyMountedKdev = deviceNodes[i]; return 0; } SLOGE("Volume %s found no suitable devices for mounting :(\n", getLabel()); setState(Volume::State_Idle); return -1;}代码中exfat相关的都是添加的部分，主要做的事情就是检测设备节点是否是exFAT文件格式，如果是就挂载它。
第三步：将exfat加入系统中编译
在device/xxx/yyy.mk中加入exfat模块。这样系统编译的时候，会把exfat相关的文件编译进系统。
注：这里的xxx/yyy请根据自己的项目来决定加在哪个mk文件中。
# ntfs-3g binaryPRODUCT_PACKAGES += \ ntfs-3g \ ntfsfix# exfat binaryPRODUCT_PACKAGES += \ mount.exfat参考文章
移植exFAT到Android4.2.2
CyanogenMod 10 修改 Vold 使 Android 自动挂载 NTFS 和 exFAT 格式的 SD 卡
源码下载
exfat
exfat android分支
ntfs-3g
Android-fs
android_external_ntfs-3g_4.4
android_external_exfat
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