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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-other.html" title="Other system interfaces, some from Windows:"><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-other.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><code class="function">close_range</code> does not support the Linux-specific |
| flag CLOSE_RANGE_UNSHARE.</p><p>The Solaris-invented ACL functions <code class="function">acl</code>, |
| <code class="function">facl</code>, <code class="function">aclcheck</code>, |
| <code class="function">aclfrommode</code>, <code class="function">aclfrompbits</code>, |
| <code class="function">aclfromtext</code>, <code class="function">aclsort</code>, |
| <code class="function">acltomode</code>, <code class="function">acltopbits</code> and |
| <code class="function">acltotext</code> and the belonging macros and datatypes |
| are defined in <cygwin/acl.h> since they collide with the |
| Linux-compatible POSIX.1e draft macros in <sys/acl.h>. Just |
| include <cygwin/acl.h> if you prefer them over the POSIX.1e |
| functions.</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><p><code class="function">fallocate</code> has a few Windows quirks: The |
| FALLOC_FL_ZERO_RANGE operation is NOT atomic. With flags set to 0 and |
| FALLOC_FL_KEEP_SIZE, sparse blocks in the given range are re-allocated |
| as per the POSIX requirements. This re-allocation operation isn't |
| atomic either. Over-allocation with FALLOC_FL_KEEP_SIZE is only |
| temporary on Windows until the last handle to the file is closed. |
| Over-allocation on sparse files is entirely ignored on Windows.</p><p><code class="function">sched_setscheduler</code> only emulates API behavior |
| because Windows does not offer alternative scheduling policies. |
| If <code class="literal">SCHED_OTHER</code> or <code class="literal">SCHED_BATCH</code> is |
| selected, the Windows priority is set according to the nice value. |
| If <code class="literal">SCHED_IDLE</code> is selected, the Windows priority is |
| set to <code class="literal">IDLE_PRIORITY_CLASS</code>. |
| If <code class="literal">SCHED_FIFO</code> or <code class="literal">SCHED_RR</code> is |
| selected, the nice value is preserved and the Windows priority is set |
| according to the <code class="literal">sched_priority</code> value. |
| If the <code class="literal">SCHED_RESET_ON_FORK</code> flag is set, realtime |
| policies and negative nice values are dropped on |
| <code class="function">fork</code>.</p><p><code class="function">nice</code>, <code class="function">setpriority</code>, |
| <code class="function">sched_setparam</code> and <code class="function">sched_setscheduler</code> |
| map the nice value (<code class="literal">SCHED_OTHER</code>, |
| <code class="literal">SCHED_BATCH</code>) or the <code class="literal">sched_priority</code> |
| (<code class="literal">SCHED_FIFO</code>, <code class="literal">SCHED_RR</code>) to Windows |
| priority classes as follows:</p><pre class="screen"> |
| SCHED_OTHER SCHED_BATCH SCHED_FIFO/RR |
| nice value nice value sched_priority Windows priority class |
| 12...19 4...19 1....6 IDLE_PRIORITY_CLASS |
| 4...11 -4....3 7...12 BELOW_NORMAL_PRIORITY_CLASS |
| -4....3 -12...-5 13...18 NORMAL_PRIORITY_CLASS |
| -12...-5 -13..-19 19...24 ABOVE_NORMAL_PRIORITY_CLASS |
| -13..-19 -20 25...30 HIGH_PRIORITY_CLASS |
| -20 - 31...32 REALTIME_PRIORITY_CLASS |
| </pre> |
| The use of values which are mapped to the |
| <code class="literal">REALTIME_PRIORITY_CLASS</code> require administrative |
| privileges. |
|
|
| </div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="std-other.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">Other system interfaces, some from Windows: </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> |
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