On Fri, Nov 08, 2019 at 10:32:51PM +0100, Arnd Bergmann wrote: > The interpretation of on-disk timestamps in HFS and HFS+ differs > between 32-bit and 64-bit kernels at the moment. Use 64-bit timestamps > consistently so apply the current 64-bit behavior everyhere. > > According to the official documentation for HFS+ [1], inode timestamps > are supposed to cover the time range from 1904 to 2040 as originally > used in classic MacOS. > > The traditional Linux usage is to convert the timestamps into an unsigned > 32-bit number based on the Unix epoch and from there to a time_t. On > 32-bit systems, that wraps the time from 2038 to 1902, so the last > two years of the valid time range become garbled. On 64-bit systems, > all times before 1970 get turned into timestamps between 2038 and 2106, > which is more convenient but also different from the documented behavior. > > Looking at the Darwin sources [2], it seems that MacOS is inconsistent in > yet another way: all timestamps are wrapped around to a 32-bit unsigned > number when written to the disk, but when read back, all numeric values > lower than 2082844800U are assumed to be invalid, so we cannot represent > the times before 1970 or the times after 2040. > > While all implementations seem to agree on the interpretation of values > between 1970 and 2038, they often differ on the exact range they support > when reading back values outside of the common range: > > MacOS (traditional): 1904-2040 > Apple Documentation: 1904-2040 > MacOS X source comments: 1970-2040 > MacOS X source code: 1970-2038 > 32-bit Linux: 1902-2038 > 64-bit Linux: 1970-2106 > hfsfuse: 1970-2040 > hfsutils (32 bit, old libc) 1902-2038 > hfsutils (32 bit, new libc) 1970-2106 > hfsutils (64 bit) 1904-2040 > hfsplus-utils 1904-2040 > hfsexplorer 1904-2040 > 7-zip 1904-2040 > > Out of the above, the range from 1970 to 2106 seems to be the most useful, > as it allows using HFS and HFS+ beyond year 2038, and this matches the > behavior that most users would see today on Linux, as few people run > 32-bit kernels any more. > > Link: [1] https://developer.apple.com/library/archive/technotes/tn/tn1150.html > Link: [2] https://opensource.apple.com/source/hfs/hfs-407.30.1/core/MacOSStubs.c.auto.html > Link: https://lore.kernel.org/lkml/20180711224625.airwna6gzyatoowe@eaf/ > Cc: Viacheslav Dubeyko <slava@xxxxxxxxxxx> > Suggested-by: "Ernesto A. Fernández" <ernesto.mnd.fernandez@xxxxxxxxx> > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> > --- Reviewed-by: Ernesto A. Fernández <ernesto.mnd.fernandez@xxxxxxxxx>
