Messages in this thread | | | From | Paolo Giarrusso <> | Date | Thu, 5 Nov 2009 21:22:45 +0100 | Subject | Daylight saving time & FAT |
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Hi, I'm an ex kernel developer, writing to you because of a problem with FAT and its Linux driver.
When re-rsync'ing two hard drives (one VFAT, one NTFS mounted with ntfs-3g) after a Daylight Saving Time change (I was on CEST, +0200, now I'm on CET, +0100), I discovered a one-hour time difference over all files (on FAT, they are one hour in future). My current understanding is that FAT stores times relative to the current timezone, and that's crappy (see fat_time_fat2unix(), in fs/fat/misc.c). But with the current code, it gets even more crappy - the same file will have a different _UTC_ timestamp depending on my current timezone, since the current offset from UTC is added to the stored timestamp to get the UTC time (I verified the timezone change would perfectly explain, even in sign, the time difference I found). That's why I guess that the FAT timestamps are wrong. I frankly doubt that Windows is so bad.
On DOS, they could get away without any conversion at all. But on current Windows systems? Either you find the right time zone at file saving time (too complicated IMHO) or ignore DST when saving/restoring time (i.e. pretend DST is not in effect, and add the shift if needed). I don't know right now what happens. I wrote this mail to discuss what would be the correct solution (the second?), and if it is possible to implement it.
Thanks for your attention Regards -- Paolo Giarrusso
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