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71 lines
3.4 KiB
Text
71 lines
3.4 KiB
Text
POSIX Divergence
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================
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The Sortix operating system cares about compatibility with existing software and
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maintaining such software by purging obsolete stuff from the system. Sortix
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recognizes the POSIX standard as valuable and embraces it rather than fighting
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it. Nonetheless, we don't implement standards for the sake of standards, but for
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the benefits we get from complying. Sometimes the standard mandates something
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that is broken or we can do considerably better. In those cases it's best to
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diverge and fix the design mistakes properly - but we must not forget there is
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a considerable compatibility cost we must pay. Don't diverge unless there is a
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good reason to and compatibility and an upgrade path must be considered.
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That said, Sortix has diverged from full POSIX compliance in the hope such
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decisions would be for the better. This document attempts to list where Sortix
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has intentionally diverged from POSIX 2008. See doc/obsolete-stuff for a more
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detailed rationale of why the interfaces are absent or scheduled for removal.
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Mind that Sortix doesn't fully intend to implement the XSI option and violations
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of that isn't listed here.
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It is worth noting that some particular interfaces scheduled for removal will
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likely take a very long time to phase out and wholly remove.
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Mandated by POSIX but not implemented in Sortix
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----
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* POSIX advisory locks (fcntl, lockf) are not implemented.
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* getpgrp is not implemented.
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* <strings.h> has been merged into <string.h>.
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* Numerous namespace violations (will be fixed or documented here).
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* Numerous missing features (will be fixed or documented here).
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Obsolescent in POSIX but not implemented in Sortix
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----
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* gets is not implemented (obsolescent in POSIX).
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* tmpnam is not implemented (obsolescent in POSIX).
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Mandated by POSIX and scheduled for Sortix removal
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----
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* select is scheduled for removal.
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* struct timeval is scheduled for removal.
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* times, <sys/times.h> is scheduled for removal.
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Obsolescent in POSIX and scheduled for Sortix removal
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---
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* asctime and asctime_r are scheduled for removal (obsolescent in POSIX).
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* ctime, ctime_r are scheduled for removal (obsolescent in POSIX).
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* utime, <utime.h> are scheduled for removal (obsolescent in POSIX).
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Signal Stacks
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-------------
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Threads are able to set a recursive signal handling stack using sigaltstack(2)
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even if SS_ONSTACK is currently set - while POSIX mandates EPERM in this case.
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Such a stack will be used for recursive signals (with SA_ONSTACK set) for the
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duration of the signal handler. The original signal stack state will be restored
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when the signal handler returns, any edit with sigaltstack will be temporary
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(unless the saved ucontext is modified).
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Timestamps
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----------
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The time_t values given by clock_gettime(CLOCK_REALTIME, ...) (and other system
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interfaces built upon that) are the number of actual seconds that has passed
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since 1970-01-01 00:00:00 UTC. This includes leap seconds, unlike the timestamps
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mandated by POSIX. This has the advantage that time_t values are unambiguously
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translate to a particular date and time and back and that the values are
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continuous and adding an internal to a time_t value actually delays by that
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interval. This has the unfortunate consequence that translating to and from
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POSIX time requires subtracting the number of leap seconds that has occurred for
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that time value. The standard library needs to get some utility functions for
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doing such conversion.
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