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+ , 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 , 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:  https://developer.apple.com/library/archive/technotes/tn/tn1150.html Link:  https://opensource.apple.com/source/hfs/hfs-407.30.1/core/MacOSStubs.c.auto.... Link: https://lore.kernel.org/lkml/20180711224625.airwna6gzyatoowe@eaf/ Cc: Viacheslav Dubeyko firstname.lastname@example.org Suggested-by: "Ernesto A. Fernández" email@example.com Signed-off-by: Arnd Bergmann firstname.lastname@example.org
Reviewed-by: Ernesto A. Fernández email@example.com