From testing on linux (rhel 7 and gentoo), it seems the timezone computed by my_system_gmt_sec is off by 7200 seconds and has a inverse sign. I am

I am working on a patch for adding datetime parsing support for RFC3339 as reported in MDEV-11829. In examining methods to use the provided offset to convert the parsed datetime to the timezone of mariadb. I have some questions on the my_system_gmt_sec function in sql-common/my_time.c . trying to determine why this is and if it is designed to be this way. From the comments in the file, it seems my_system_gmt_sec was designed specifically due to cross-platform issues. However there is no mention that it the timezone computed is suppose to be off or have an inverse sign. I could not find any usages of the my_time_zone global variable or where another function used the timezone computed by my_system_gmt_sec, so this might not effect anything, but I wanted some clarification. Here is some testing results: | ---------------------------- | ------------------------------------------ | -------------- | | Server TimeZone | my_system_gmt_sec timezone | Difference | | ---------------------------- | ------------------------------------------ | -------------- | | -18000 (-05:00 EST) | 25200 | 43200 | | 3600 (+01:00 CET) | -10800 | 14400 | | 0 (+00:00 GMT) | 7200 | 7200 | | ---------------------------- | ------------------------------------------ | -------------- | In testing I've been able to determine that the 7200 second deviation is caused by compensating for the "-3600" seconds twice, first in setting an initial timezone in my_init_time: https://github.com/MariaDB/server/blob/10.1/sql-common/my_time.c#L709 Inside my_system_gmt_sec the "current_timezone" is set to the "my_time_zone" which is at 3600 initially. Then below another 3600 is added to the timezone computation: https://github.com/MariaDB/server/blob/10.1/sql-common/my_time.c#L946 The diff variable that is computed has the correct offset, with an inverse sign. If current_timezone were set to "diff" then it would have the correct timezone but again with an inverse sign. The inverse sign comes from the doing t - l_time instead of l_time - t. Should the timezone computed have an inverse sign? Is there a reason it is offset by 7200 seconds? Perhaps the behavior is different on other platform, that I have not tested. Thank you, Seth Shelnutt