diff --git a/fs/Vfat.cpp b/fs/Vfat.cpp index f3f04d8..c0cd918 100644 --- a/fs/Vfat.cpp +++ b/fs/Vfat.cpp @@ -20,6 +20,7 @@ #include #include #include +#include #include #include @@ -118,6 +119,16 @@ status_t Check(const std::string& source) { return 0; } +int16_t currentUtcOffsetMinutes() { + time_t now = time(NULL); + + struct tm nowTm; + localtime_r(&now, &nowTm); + + int32_t utcOffsetSeconds = nowTm.tm_gmtoff; + return (int16_t)(utcOffsetSeconds / 60); +} + status_t Mount(const std::string& source, const std::string& target, bool ro, bool remount, bool executable, int ownerUid, int ownerGid, int permMask, bool createLost) { int rc; @@ -136,6 +147,33 @@ status_t Mount(const std::string& source, const std::string& target, bool ro, bo android::base::StringPrintf("utf8,uid=%d,gid=%d,fmask=%o,dmask=%o,shortname=mixed", ownerUid, ownerGid, permMask, permMask); + // b/315058275: Set this to false if you don't want to use a fixed offset + // determined at mount time. When this is false, the vfat driver will fall + // back to using sys_tz, which Android does not set by default, then assume + // local time == UTC. + if (true) { + // Calculate the offset to use to adjust FAT timestamps to convert them + // from "local time" into unix epoch time. This assumes the current UTC + // offset of this device is the same as the device that wrote them. User + // space code, e.g. ls -l, will then apply the UTC offset for the UTC + // time to convert times from unix epoch time to local time for display. + // Before Android U (b/246256335), Android platform code informed the + // Linux kernel about the UTC offset under some circumstances, but not + // for all, e.g. DST changes. The kernel vfat driver is one of the few + // things in the kernel that tries to use kernel UTC offset information. + // Setting time zone offset in the Linux kernel is discouraged and so + // Android no longer informs the kernel. Instead, the offset for vfat + // to use is now set at volume mount time. This means that if the time + // zone offset changes while the device is mounted, or if files were + // written in opposing daylight saving time, then incorrect file times + // will be displayed until the volume is remounted. Even then, the vfat + // driver has to assume a fixed offset to apply to all files, so files + // written at different times of the year can have incorrect times + // calculated, e.g. offset incorrectly by one hour. + int16_t timeOffsetArg = currentUtcOffsetMinutes(); + mountData += android::base::StringPrintf(",time_offset=%d", timeOffsetArg); + } + rc = mount(c_source, c_target, "vfat", flags, mountData.c_str()); if (rc && errno == EROFS) {