| Message ID | 20200801112007.2148-1-von81@163.com |
|---|---|
| State | Rejected |
| Headers | show |
| Series | rtc: interface:: 1969-12-31T23:59:59 is set as rtc_time if rtc_time is invalid in __rtc_read_time | expand |
Hi, On 01/08/2020 19:20:07+0800, Grant Feng wrote: > 1969-12-31T23:59:59 is an error more clear than Invalid argument Definitively not, 1969-12-31T23:59:59 is a valid date and should not be returned when it is known the current date is not set in the RTC. > > For example, when the RTC clock is not set, it will print a kernel > error log every time someone tries to read the clock: > ~ # hwclock -r > hwclock: RTC_RD_TIME: Invalid argument > > It's clear and easy to understand what happened if print > 1969-12-31T23:59:59 in this situation： > ~ # hwclock -r > Wed Dec 31 23:59:59 1969 0.000000 seconds > How do you know this is an error an not what is actually set on the RTC?
Hi, On 2020-08-01 21:28, Alexandre Belloni wrote: > On 01/08/2020 19:20:07+0800, Grant Feng wrote: >> 1969-12-31T23:59:59 is an error more clear than Invalid argument > Definitively not, 1969-12-31T23:59:59 is a valid date and should not be > returned when it is known the current date is not set in the RTC. 'rtc_valid_tm' is used to check rtc_time and 1969-12-31T23:59:59 is invalid. when the RTC clock is not set, some rtc devices always return '0' or almost random data, and different rtc devices may give different return data. so, I think, it's usful to return a default date when the current date is not set in the RTC. >> For example, when the RTC clock is not set, it will print a kernel >> error log every time someone tries to read the clock: >> ~ # hwclock -r >> hwclock: RTC_RD_TIME: Invalid argument >> >> It's clear and easy to understand what happened if print >> 1969-12-31T23:59:59 in this situation： >> ~ # hwclock -r >> Wed Dec 31 23:59:59 1969 0.000000 seconds >> > How do you know this is an error an not what is actually set on the RTC? 'rtc_valid_tm' will check rtc_time when someone set the RTC, the time should not be earlier than 1970-1-1T00:00:00. so 1969-12-31T23:59:59 can not be actually set on the RTC. When someone get ~ # hwclock -r Wed Dec 31 23:59:59 1969 0.000000 seconds he knows: the RTC time doesn't match my watch, change it now. but still lots of people don't know what happened if they see ~ # hwclock -r hwclock: RTC_RD_TIME: Invalid argument Grant Feng Embedded Linux and Kernel engineering RTCHIP Information Technology (Shanghai) Co., Ltd.
On 02/08/2020 14:51:41+0800, Grant Feng wrote: > On 2020-08-01 21:28, Alexandre Belloni wrote: > > On 01/08/2020 19:20:07+0800, Grant Feng wrote: > > > 1969-12-31T23:59:59 is an error more clear than Invalid argument > > Definitively not, 1969-12-31T23:59:59 is a valid date and should not be > > returned when it is known the current date is not set in the RTC. > 'rtc_valid_tm' is used to check rtc_time and 1969-12-31T23:59:59 is invalid. > when the RTC clock is not set, some rtc devices always return '0' or almost > random data, and different rtc devices may give different return data. > so, I think, it's usful to return a default date when the current date is > not set in the RTC. You are not solving the issue you mention here. If the RTC doesn't know whether the date/time is invalid and the core think it is valid, then your code will not run. > > > For example, when the RTC clock is not set, it will print a kernel > > > error log every time someone tries to read the clock: > > > ~ # hwclock -r > > > hwclock: RTC_RD_TIME: Invalid argument > > > > > > It's clear and easy to understand what happened if print > > > 1969-12-31T23:59:59 in this situation： > > > ~ # hwclock -r > > > Wed Dec 31 23:59:59 1969 0.000000 seconds > > > > > How do you know this is an error an not what is actually set on the RTC? > 'rtc_valid_tm' will check rtc_time when someone set the RTC, the time > should not be earlier than 1970-1-1T00:00:00. so 1969-12-31T23:59:59 > can not be actually set on the RTC. > When someone get > ~ # hwclock -r > Wed Dec 31 23:59:59 1969 0.000000 seconds > he knows: the RTC time doesn't match my watch, change it now. > but still lots of people don't know what happened if they see > ~ # hwclock -r > hwclock: RTC_RD_TIME: Invalid argument > This makes userspace checking for errors way worse. Think about it, first userspace will need to check for an error when calling the ioctl then it will have to check the time and consider a vlid date invalid. Seriously, if hwclock doesn't do what you want, you can either patch it or use another tool.
Thank you for explaining that. On 2020-08-02 21:04, Alexandre Belloni wrote: > On 02/08/2020 14:51:41+0800, Grant Feng wrote: >> On 2020-08-01 21:28, Alexandre Belloni wrote: >>> On 01/08/2020 19:20:07+0800, Grant Feng wrote: >>>> 1969-12-31T23:59:59 is an error more clear than Invalid argument >>> Definitively not, 1969-12-31T23:59:59 is a valid date and should not be >>> returned when it is known the current date is not set in the RTC. >> 'rtc_valid_tm' is used to check rtc_time and 1969-12-31T23:59:59 is invalid. >> when the RTC clock is not set, some rtc devices always return '0' or almost >> random data, and different rtc devices may give different return data. >> so, I think, it's usful to return a default date when the current date is >> not set in the RTC. > You are not solving the issue you mention here. If the RTC doesn't know > whether the date/time is invalid and the core think it is valid, then > your code will not run. > >>>> For example, when the RTC clock is not set, it will print a kernel >>>> error log every time someone tries to read the clock: >>>> ~ # hwclock -r >>>> hwclock: RTC_RD_TIME: Invalid argument >>>> >>>> It's clear and easy to understand what happened if print >>>> 1969-12-31T23:59:59 in this situation： >>>> ~ # hwclock -r >>>> Wed Dec 31 23:59:59 1969 0.000000 seconds >>>> >>> How do you know this is an error an not what is actually set on the RTC? >> 'rtc_valid_tm' will check rtc_time when someone set the RTC, the time >> should not be earlier than 1970-1-1T00:00:00. so 1969-12-31T23:59:59 >> can not be actually set on the RTC. >> When someone get >> ~ # hwclock -r >> Wed Dec 31 23:59:59 1969 0.000000 seconds >> he knows: the RTC time doesn't match my watch, change it now. >> but still lots of people don't know what happened if they see >> ~ # hwclock -r >> hwclock: RTC_RD_TIME: Invalid argument >> > This makes userspace checking for errors way worse. Think about it, first > userspace will need to check for an error when calling the ioctl then it > will have to check the time and consider a vlid date invalid. Seriously, > if hwclock doesn't do what you want, you can either patch it or use > another tool. >
Thank you again for your patience to explain. I get the log and now I get it. commit 812318a094d0715194d9f686b22ee67e7dc59d93 Author: Alexandre Belloni <alexandre.belloni@bootlin.com> Date: Wed Feb 21 11:44:26 2018 +0100 rtc: cmos: let the core handle invalid time Setting the rtc to a valid time when the time is invalid is a bad practice, because then userspace doesn't know it shouldn't trust the RTC. Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com> then you removed the following code fragment in "drivers/rtc/rtc-cmos.c": - cmos_read_time(&pdev->dev, &time); - ret = rtc_valid_tm(&time); - if (ret) { - struct rtc_time def_time = { - .tm_year = 1, - .tm_mday = 1, - }; - cmos_set_time(&pdev->dev, &def_time); - } On 2020-08-02 21:04, Alexandre Belloni wrote: > On 02/08/2020 14:51:41+0800, Grant Feng wrote: >> On 2020-08-01 21:28, Alexandre Belloni wrote: >>> On 01/08/2020 19:20:07+0800, Grant Feng wrote: >>>> 1969-12-31T23:59:59 is an error more clear than Invalid argument >>> Definitively not, 1969-12-31T23:59:59 is a valid date and should not be >>> returned when it is known the current date is not set in the RTC. >> 'rtc_valid_tm' is used to check rtc_time and 1969-12-31T23:59:59 is invalid. >> when the RTC clock is not set, some rtc devices always return '0' or almost >> random data, and different rtc devices may give different return data. >> so, I think, it's usful to return a default date when the current date is >> not set in the RTC. > You are not solving the issue you mention here. If the RTC doesn't know > whether the date/time is invalid and the core think it is valid, then > your code will not run. > >>>> For example, when the RTC clock is not set, it will print a kernel >>>> error log every time someone tries to read the clock: >>>> ~ # hwclock -r >>>> hwclock: RTC_RD_TIME: Invalid argument >>>> >>>> It's clear and easy to understand what happened if print >>>> 1969-12-31T23:59:59 in this situation： >>>> ~ # hwclock -r >>>> Wed Dec 31 23:59:59 1969 0.000000 seconds >>>> >>> How do you know this is an error an not what is actually set on the RTC? >> 'rtc_valid_tm' will check rtc_time when someone set the RTC, the time >> should not be earlier than 1970-1-1T00:00:00. so 1969-12-31T23:59:59 >> can not be actually set on the RTC. >> When someone get >> ~ # hwclock -r >> Wed Dec 31 23:59:59 1969 0.000000 seconds >> he knows: the RTC time doesn't match my watch, change it now. >> but still lots of people don't know what happened if they see >> ~ # hwclock -r >> hwclock: RTC_RD_TIME: Invalid argument >> > This makes userspace checking for errors way worse. Think about it, first > userspace will need to check for an error when calling the ioctl then it > will have to check the time and consider a vlid date invalid. Seriously, > if hwclock doesn't do what you want, you can either patch it or use > another tool. >
diff --git a/drivers/rtc/interface.c b/drivers/rtc/interface.c index 794a4f036b99..e6b3f4163565 100644 --- a/drivers/rtc/interface.c +++ b/drivers/rtc/interface.c @@ -101,8 +101,20 @@ static int __rtc_read_time(struct rtc_device *rtc, struct rtc_time *tm) rtc_add_offset(rtc, tm); err = rtc_valid_tm(tm); - if (err < 0) + if (err < 0) { dev_dbg(&rtc->dev, "read_time: rtc_time isn't valid\n"); + + tm->tm_sec = 59; + tm->tm_min = 59; + tm->tm_hour = 23; + tm->tm_mday = 31; + tm->tm_mon = 11; + tm->tm_year = 69; + tm->tm_wday = 3; + tm->tm_yday = 365; + tm->tm_isdst = 0; + } + err = 0; } return err; }
1969-12-31T23:59:59 is an error more clear than Invalid argument For example, when the RTC clock is not set, it will print a kernel error log every time someone tries to read the clock: ~ # hwclock -r hwclock: RTC_RD_TIME: Invalid argument It's clear and easy to understand what happened if print 1969-12-31T23:59:59 in this situation： ~ # hwclock -r Wed Dec 31 23:59:59 1969 0.000000 seconds Signed-off-by: Grant Feng <von81@163.com> --- drivers/rtc/interface.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-)