On Wed, Jun 20, 2018 at 5:51 PM, Coly Li colyli@suse.de wrote:
On 2018/6/20 5:51 PM, Arnd Bergmann wrote:
bcache uses get_seconds() to read the current system time and store it in the superblock as well as in uuid_entry structures that are user visible.
This changes over from the deprecated function to ktime_get_real_seconds(), which returns a 64-bit timestamp as it should. Unfortunately, the two structures are still limited to 32 bits, so this won't fix any real problems. Let's at least document that properly, in case we get an updated format in the future it can be fixed. Until then, we still have some time, and checking the tools at https://github.com/koverstreet/bcache-tools reveals no access to any of them.
Signed-off-by: Arnd Bergmann arnd@arndb.de
Hi Arnd,
Firstly thanks to your patch, especially the detailed information in patch log, it helps me to understand the problem more easier.
From the information, it seems the problem is current 32bit time stamp will be overflow in 2106. So it will be 88 years later, which I have to say I don't care.
Also for get_seconds() which works well for current code as many other places call it, I would like to keep it.
I'm currently in the process of removing all instances of get_seconds() with patches like this. In many cases, we actually want to use ktime_get_seconds() to return a monotonic time that is immune to concurrent setttimeofday() calls, in others the code needs to be changed to avoid the y2038 overflow. For bcache, we don't really need either of them, but I'd still want to move over everything to ktime_get_* based interfaces.
Should I clarify that motivation in the changelog text further?
I can also do a simple replacement of get_seconds() with ktime_get_real_seconds() throughout bcache instead of adding the intermediate helper function.
Arnd