On 11/09/2021 10:05:02-0700, Linus Torvalds wrote: > On Sat, Sep 11, 2021 at 8:59 AM Alexandre Belloni > <alexandre.belloni@xxxxxxxxxxx> wrote: > > > > The broken down time conversion is similar to what is done > > in the time subsystem since v5.14. > > By "similar" you mean "identical", no? > > Why is the rtc subsystem not just using the generic time64_to_tm()? > > Yes, yes, I realize that due to historical mistakes, there's a > duplicate 'struct rtc_time' struct, but it turns out that that is > _identical_ to 'struct tm' except it also has a 'int tm_isdst' at the > end. > > So you could literally make a union of the two, pass the 'struct tm' > part down to the generic code, and just do > > rtc_tm->tm_isdst = 0; > > at the end. > > Rather than have a duplicate copy of that admittedly clever Neri and > Schneider algorithm. > > Hmm? > Yes, most of it is historical, I did have a look at removing the copy but at the time, rtc_time64_to_tm was slightly more efficient because it knew the time was positive. The other issue is that struct rtc_time is exposed to userspace while the kernel struct tm is not and this would tie both struct and if you look close enough, struct tm has long tm_year and struct rtc_time has int tm_year which on 32-bit ARM has a different size. I've been reluctant to change struct tm because I didn't take the time to check the impact on all the users (IIRC, mainly in filesystems). -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
