From 4fd65aec913a1b99e8d748a7a82c150b8f7ee510 Mon Sep 17 00:00:00 2001 From: Laurent Bercot Date: Fri, 2 Jan 2015 10:15:29 +0000 Subject: Remove the --enable-right-tz configure option. Make it a run-time autodetection instead. Update doc. Thanks to Paul Jarc for the suggestion. --- doc/flags.html | 58 ++++++++-------------------------------------- doc/libstddjb/djbtime.html | 13 ++++------- doc/libstddjb/tai.html | 2 +- 3 files changed, 15 insertions(+), 58 deletions(-) (limited to 'doc') diff --git a/doc/flags.html b/doc/flags.html index a7bdab8..f519685 100644 --- a/doc/flags.html +++ b/doc/flags.html @@ -71,7 +71,7 @@ tested, so it's usually safe, and faster, to stick to the default.

--enable-tai-clock

- To understand what this flag is about - and the next three flags too - you + To understand what this flag is about - and the next two flags too - you should start by reading this page about Unix time, @@ -105,10 +105,13 @@ and makes event loop handling (with functions such as

  • ↑ skalibs uses TAI internally; setting your system clock to TAI-10 saves a lot of conversions and makes time computations with skalibs more efficient.
    • -
  • → In order to display GMT or local time properly, you have to -use the right/ timezones from Arthur David Olson's timezone -library. If your libc does not support them, see the -next flag.
    • +
  • → skalibs-aware software will display GMT or local time properly in +every case, but you have to +use the right/ timezones, from Arthur David Olson's timezone +library, to prevent your other software from being confused by a TAI-10 system clock. +If you do not use right/ timezones, utilities such as date +will not compute the proper time - they will have an offset of 24 seconds +or so.
  • ↓ This setup is arguably not SUSv4 conformant (a strict interpretation of Single Unix requires the system clock to be set to UTC).
  • ↓ This setup is not compatible with @@ -126,7 +129,8 @@ POSIX setup:
  • ↑ This is strictly SUSv4-compliant. Most Unix machines all over the world are set up like this.
  • ↑ This is compatible with ntpd.
    • -
  • → You should not use Olson's time library in that case.
    • +
  • → You should use posix/ time zones in that case, +not right/ time zones.
  • ↓ skalibs time computations will take a bit more processing power.
  • ↓ Most importantly, you forsake all linearity - and even monotonicity - on your system clock, which can now only be used as a wall clock, @@ -154,48 +158,6 @@ POSIX freak, or your Unix distribution is running ntpd for you, or other software is assuming you're on UTC. This is the default.

    - -

    --enable-right-tz

    - -

    - This option instructs skalibs that you're using Olson's time -library, i.e. "right/" timezones. -

    - -

    - Normally, if you set --enable-tai-clock, you -should also set up your timezone to a "right/" one, and -set flag-tzisright. And if you don't use ---enable-tai-clock, you should also use a POSIX -timezone, and NOT use --enable-right-tz. Those two options -should always be used together. -

    - -

    - But some C libraries do not support the Olson time library's -timezone format, and just do not provide the "right/" timezones! For -instance, musl, -an alternative libc for Linux, only supports POSIX timezones. And you -might want to use such a libc, and still set up your clock to -TAI-10, for instance in embedded environments where accurate timekeeping -is important. In such cases, you'll set up a POSIX timezone, and use the ---enable-tai-clock option without the --enable-right-tz one. -

    - -

    - Be aware that setting your system clock to TAI-10 without having a -"right/" timezone will cause non-skalibs-using software to display -local time incorrectly; in such a setup, only skalibs-using software -will understand what is going on and do the proper computations to -display the correct local time. Keep your settings as consistent as -possible. -

    - -

    - By default, skalibs will consider you are using POSIX timezones (as well -as a UTC system clock). -

    -

    --enable-clock

    diff --git a/doc/libstddjb/djbtime.html b/doc/libstddjb/djbtime.html index 45876c8..2fa3071 100644 --- a/doc/libstddjb/djbtime.html +++ b/doc/libstddjb/djbtime.html @@ -107,15 +107,10 @@ error occurs (for instance: the leap second table cannot be found).

    The following functions convert time between an internal representation -and a broken-down struct tm. The ---enable-right-tz configure option is used in -determining how the conversion should proceed. If the --enable-tai-clock -and --enable-right-tz configure options have been both enabled -or both disabled, everything is naturally -converted as it should be. If only one of them has been enabled, -unholy magic happens here -to get the correct broken-down time despite the timezone definition being -wrong. +and a broken-down struct tm. Conversions are performed to +get leap seconds handling right, depending on whether skalibs has been +configured for a TAI-10 or a UTC system clock, and on whether the current +timezone takes leap seconds into account or not.

    diff --git a/doc/libstddjb/tai.html b/doc/libstddjb/tai.html index 3524c05..3617959 100644 --- a/doc/libstddjb/tai.html +++ b/doc/libstddjb/tai.html @@ -55,7 +55,7 @@ on time. It's outdated (there was a leap second in 2009), but complete.

    • page about leap seconds, UTC and TAI.
  • The skalibs --enable-tai-clock -and --enable-right-tz documentation.
    • +documentation.
  • Dan J. Bernstein's page on UTC, TAI and Unix time.
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