android 限定Mtp映射目录大小

来源：互联网发布：2017nba球员数据排名编辑：程序博客网时间：2024/05/16 15:25

功能需求：限定Mtp目录的大小，比如4G，即使映射的外置存储空间（SD－card）大于4GB，目录容量也就4G，小于 4G的外部存储则按原大小处理。

软件平台：android 4.4.2

看到这个需求，一开始的考虑是单给mtp映射到外置sdcard的目录建立一个4G的分区，当然这不是相对较优的解决方向；后来查看向相关目录拷贝文件时，mtpserver的log看，mtpservice一直在查看存储介质剩余的存储空间，于是打算从获取剩余空间的jni接口中做这层管卡。

--- a/frameworks/av/media/mtp/MtpStorage.cpp
+++ b/frameworks/av/media/mtp/MtpStorage.cpp
@@ -35,6 +35,8 @@

namespace android {

+const uint64_t gbSpace = 1024L*1024L*1024L; //1GB
+
MtpStorage::MtpStorage(MtpStorageID id, const char* filePath,
const char* description, uint64_t reserveSpace,
bool removable, uint64_t maxFileSize)
@@ -87,15 +89,42 @@ uint64_t MtpStorage::getMaxCapacity() {
}

uint64_t MtpStorage::getFreeSpace() {
+ int i = 0;
+ FILE *fstream=NULL;
+ char buff[128];
+ char length[128];
struct statfs stat;
+ memset(buff, 0, sizeof(buff));
+ memset(length, 0, sizeof(length));
+
if (statfs(getPath(), &stat))
return -1;
uint64_t freeSpace = (uint64_t)stat.f_bavail * (uint64_t)stat.f_bsize;
+ if (4*gbSpace > freeSpace)
+ return (freeSpace > mReserveSpace ? freeSpace - mReserveSpace : 0);

//ALPS00120037,Added for USB Develpment debug, more log for more debuging help
+ //sxlog_printf(ANDROID_LOG_INFO, "MtpStorage",
+ // "MtpStorage::getFreeSpace: freeSpace = %lld, mReserveSpace = %lld \n", freeSpace, mReserveSpace);
+ //ALPS00120037,Added for USB Develpment debug, more log for more debuging help
+
+ fstream = popen("du -sk /storage/sdcard1/music/","r");
+ if (NULL != fgets(buff, sizeof(buff), fstream)) {
+ while (buff[i] != '\t') {
+ length[i] = buff[i];
+ i++;
+ }
+ }
+ pclose(fstream);
+
+ unsigned long long used = ((unsigned long long)strtol(length, NULL, 10)) * 1024L;//此处注意红色标示部分，否则到2G的时候，就显示空间为0了（溢出错误）。
+ if (4*gbSpace <= used) {
+ return 0;
+ } else {
+ freeSpace = (4*gbSpace) - used;
+ }
sxlog_printf(ANDROID_LOG_INFO, "MtpStorage",
"MtpStorage::getFreeSpace: freeSpace = %lld, mReserveSpace = %lld \n", freeSpace, mReserveSpace);

return (freeSpace > mReserveSpace ? freeSpace - mReserveSpace : 0);
}

过程还是比较简洁的，但最终达到的效果却是不容小视。。。

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