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Merge "Add time_offset=<UTC offset> to mount arguments" into main

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Neil Fuller 2024-01-19 17:26:00 +00:00 committed by Gerrit Code Review
commit 5b711b10db
1 changed files with 38 additions and 0 deletions
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38
fs/Vfat.cpp
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@ -20,6 +20,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <linux/fs.h>
@ -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) {