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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968"><title>Implementation Notes</title><link rel="stylesheet" type="text/css" href="docbook.css"><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"><link rel="home" href="cygwin-api.html" title="Cygwin API Reference"><link rel="up" href="compatibility.html" title="Chapter 1. Compatibility"><link rel="prev" href="std-notimpl.html" title="NOT implemented system interfaces from the Single Unix Specification, Volume 7:"><link rel="next" href="cygwin-functions.html" title="Chapter 2. Cygwin Functions"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Implementation Notes</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="std-notimpl.html">Prev</a> </td><th width="60%" align="center">Chapter 1. Compatibility</th><td width="20%" align="right"> <a accesskey="n" href="cygwin-functions.html">Next</a></td></tr></table><hr></div><div class="sect1"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="std-notes"></a>Implementation Notes</h2></div></div></div><p><code class="function">chroot</code> only emulates a chroot function call
by keeping track of the current root and accomodating this in the file
related function calls. A real chroot functionality is not supported by
Windows however.</p><p><code class="function">clock_nanosleep</code> currently supports only
CLOCK_REALTIME and CLOCK_MONOTONIC. <code class="function">clock_setres</code>,
<code class="function">clock_settime</code>, and <code class="function">timer_create</code>
currently support only CLOCK_REALTIME.</p><p>POSIX file locks via <code class="function">fcntl</code> or
<code class="function">lockf</code>, as well as BSD <code class="function">flock</code> locks
are advisory locks. They don't interact with Windows mandatory locks, nor
do POSIX fcntl locks interfere with BSD flock locks or vice versa.</p><p>BSD file locks created via <code class="function">flock</code> are only
propagated to the direct parent process, not to grand parents or sibling
processes. The locks are only valid in the creating process, its parent
process, and subsequently started child processes sharing the same file
descriptor.</p><p>In very rare circumstances an application would want to use Windows
mandatory locks to interact with non-Cygwin Windows processes accessing the
same file (databases, etc). For these purposes, the entire locking mechanism
(fcntl/flock/lockf) can be switched to Windows mandatory locks on a
per-descriptor/per-process basis. For this purpose, use the call
</p><pre class="screen">
fcntl (fd, F_LCK_MANDATORY, 1);
</pre><p>
After that, all file locks on this descriptor will follow Windows mandatory
record locking semantics: Locks are per-descriptor/per-process; locks are not
propagated to child processes, not even via <code class="function">execve</code>;
no atomic replacement of read locks with write locks and vice versa on the
same descriptor; locks have to be unlocked exactly as they have been locked.
</p><p><code class="function">fpclassify</code>, <code class="function">isfinite</code>,
<code class="function">isgreater</code>, <code class="function">isgreaterequal</code>,
<code class="function">isinf</code>, <code class="function">isless</code>,
<code class="function">islessequal</code>, <code class="function">islessgreater</code>,
<code class="function">isnan</code>, <code class="function">isnormal</code>,
<code class="function">isunordered</code>, and <code class="function">signbit</code>
only support float and double arguments, not long double arguments.</p><p><code class="function">getitimer</code> and <code class="function">setitimer</code>
only support ITIMER_REAL for now.</p><p><code class="function">link</code> will fail on FAT, FAT32, and other filesystems
not supporting hardlinks, just as on Linux.</p><p><code class="function">lseek</code> only works properly on files opened in
binary mode. On files opened in textmode (via mount mode or explicit
open flag) its positioning is potentially unreliable.</p><p><code class="function">setuid</code> is only safe against reverting the user
switch after a call to one of the exec(2) functions took place. Windows
doesn't support a non-revertable user switch within the context of Win32
processes.</p><p><code class="function">vfork</code> just calls <code class="function">fork</code>.</p><p><code class="function">vhangup</code> and <code class="function">revoke</code> always
return -1 and set errno to ENOSYS. <code class="function">grantpt</code> and
<code class="function">unlockpt</code> always just return 0.</p><p>The XSI IPC functions <code class="function">semctl</code>,
<code class="function">semget</code>, <code class="function">semop</code>,
<code class="function">shmat</code>, <code class="function">shmctl</code>,
<code class="function">shmdt</code>, <code class="function">shmget</code>,
<code class="function">msgctl</code>, <code class="function">msgget</code>,
<code class="function">msgrcv</code> and <code class="function">msgsnd</code> are only
available when cygserver is running.</p><p>The Linux-specific function <code class="function">quotactl</code> only implements
what works on Windows: Windows only supports user block quotas on NTFS, no
group quotas, no inode quotas, no time constraints.</p><p><code class="function">qsort_r</code> is available in both BSD and GNU flavors,
depending on whether _BSD_SOURCE or _GNU_SOURCE is defined when compiling.</p><p>The Linux-specific function <code class="function">renameat2</code> only
supports the RENAME_NOREPLACE flag.</p><p><code class="function">basename</code> is available in both POSIX and GNU flavors,
depending on whether libgen.h is included or not.</p><p><code class="function">sigpause</code> is available in both BSD and SysV/XSI
flavors, depending on whether _XOPEN_SOURCE is defined when compiling.</p><p><code class="function">strerror_r</code> is available in both POSIX and GNU
flavors, depending on whether _GNU_SOURCE is defined when compiling.</p><p><code class="function">dladdr</code> always sets the Dl_info members dli_sname and
dli_saddr to NULL, indicating no symbol matching addr could be found.</p><p><code class="function">getrlimit</code> resources RLIMIT_AS, RLIMIT_CPU,
RLIMIT_FSIZE, RLIMIT_DATA always return rlim_cur and rlim_max as RLIM_INFINITY,
so <code class="function">setrlimit</code> returns -1 and sets EINVAL if they are
lowered, or returns 0 if unchanged.
<code class="function">getrlimit</code> resource RLIMIT_NOFILE always returns rlim_cur
and rlim_max as OPEN_MAX; <code class="function">setrlimit</code> returns 0 sets EINVAL
if rlim_cur > rlim_max, does not change the value if it is RLIM_INFINITY,
otherwise returns the result from <code class="function">setdtablesize</code>.
<code class="function">getrlimit</code>/<code class="function">setrlimit</code> resources
RLIMIT_CORE and RLIMIT_STACK return the current values and set the requested
values.
All other resource arguments return -1 and set EINVAL.</p></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="std-notimpl.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="compatibility.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="cygwin-functions.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">NOT implemented system interfaces from the Single Unix Specification, Volume 7: </td><td width="20%" align="center"><a accesskey="h" href="cygwin-api.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 2. Cygwin Functions</td></tr></table></div></body></html>