<function>CreateProcess</function> or <function>ShellExecute</function>
to start other applications.</para>
-<para>When a Cygwin application is started, the Win32 idea of the current
-working directory (CWD) is set to an <emphasis role='bold'>invalid</emphasis>
-directory. This works around the problem that the Win32 CWD is locked
-in a way which restricts certain POSIX functionality. However, the side
-effect is that a call to, for instance, <function>CreateFile ("foo",
-...);</function> will fail, since the Win32 notion of the CWD is
-not the same as the Cygwin notion of the CWD, and worse, it's a
-directory entirely unsuitable for normal file operations.</para>
-
-<para>So, in general, don't use the Win32 file API in Cygwin applications.
-If you <emphasis role='bold'>really</emphasis> need to access files using
-the Win32 API, or if you <emphasis role='bold'>really</emphasis> have to use
-<function>CreateProcess</function> to start applications, rather than
-the POSIX <function>exec(3)</function> familiy of functions, you have to
-make sure that the Win32 CWD is set to some valid directory. To
-accomplish that, you can choose from several methods.</para>
+<para>When a Cygwin application is started, the Windows idea of the current
+working directory (CWD) is not necessarily the same as the Cygwin CWD.
+There are a couple of restrictions in the Win32 API, which disallow certain
+directories as Win32 CWD:</para>
<itemizedlist spacing="compact">
<listitem>
- <para>The easiest method is to call</para>
-
-<screen>
- #include <sys/cygwin.h>
-
- cygwin_internal (CW_SYNC_WINCWD);
-</screen>
-
- <para>prior to calling the Win32 functions which require a valid Win32 CWD.
- This function synchronizes the Win32 CWD with the Cygwin CWD.</para>
-
- <para>Note that the <function>cygwin_internal (CW_SYNC_WINCWD)</function>
- call may fail. In that case, it returns with a non-zero value and
- errno is set appropriately:</para>
-
- <segmentedlist>
- <?dbhtml list-presentation="table"?>
- <seglistitem>
- <seg><emphasis role='bold'>ENOTDIR</emphasis></seg>
- <seg>The Cygwin CWD is a virtual path, like /proc, or //, which does not
- exist as valid directory in the Win32 namespace.</seg>
- </seglistitem>
- <seglistitem>
- <seg><emphasis role='bold'>EACCES</emphasis></seg>
- <seg>The Cygwin CWD is a directory with restrictive permissions,
- which make it unusable as Win32 directory.</seg>
- </seglistitem>
- <seglistitem>
- <seg><emphasis role='bold'>ENAMETOOLONG</emphasis></seg>
- <seg>The Cygwin CWD is too long to be used as Win32 CWD.
- The Win32 CWD is restricted to 258 characters.</seg>
- </seglistitem>
- </segmentedlist>
-
- <para>You should make sure that you test the return value of
- <function>cygwin_internal (CW_SYNC_WINCWD)</function>, otherwise
- your application will potentially not work correctly. If the call
- failed, you can use the Win32 call <function>SetCurrentDirectory</function>
- to move to some well-known directory.</para>
-
- <note><para>After you've synchronized the Win32 CWD with the Cygwin CWD,
- be aware that the directory is locked, until the process exited, or
- until the process set the Win32 CWD to some other directory. During that
- period it will not be possible to rename or remove the directory from
- other Cygwin applications.</para></note>
+ <para>The Windows subsystem only supports CWD paths of up to 258 chars.
+ This restriction doesn't apply for Cygwin processes, at least not as
+ long as they use the POSIX API (chdir, getcwd). This means, if a Cygwin
+ process has a CWD using an absolute path longer than 258 characters, the
+ Cygwin CWD and the Windows CWD differ.</para>
</listitem>
+
<listitem>
- <para>If you know where to go to, you can also just call the Win32 function
- <function>SetCurrentDirectory</function> immediately.</para>
+ <para>The Win32 API call to set the current directory,
+ <function>SetCurrentDirectory</function>, fails for directories for which
+ the user has no permissions, even if the user is an administrator. This
+ restriction doesn't apply for Cygwin processes, if they are running under
+ an administrator account.</para>
</listitem>
+
<listitem>
- <para>If you need a valid Win32 CWD only for a child application started
- via <function>CreateProcess</function> and friends, you don't have to
- set your own Win32 CWD. In that case, just utilize the lpCurrentDirectory
- parameter. See the description of the <function>CreateProcess</function>
- function in the MSDN manual pages.</para>
+ <para><function>SetCurrentDirectory</function> does not support
+ case-sensitive filenames.
+ </para>
</listitem>
+
<listitem>
- <para>Last, but not least, if you don't need any POSIX function from
- Cygwin in your specific applciation, consider to compile your application
- as native Win32 (mingw) executable, rather than as Cygwin executable.</para>
+ <para>Last, but not least, <function>SetCurrentDirectory</function> can't
+ work on virtual Cygwin paths like /proc or /cygdrive. These paths only
+ exists in the Cygwin realm so they have no meaning to a native Win32
+ process.</para>
</listitem>
</itemizedlist>
+<para>As long as the Cygwin CWD is usable as Windows CWD, the Cygwin and
+Windows CWDs are in sync within a process. However, if the Cygwin process
+changes its working directory into one of the directories which are
+unusable as Windows CWD, we're in trouble. If the process uses the
+Win32 API to access a file using a relative pathname, the resulting
+absolute path would not match the expectations of the process. In the
+worst case, the wrong files are deleted.</para>
+
+<para>To workaround this problem, Cygwin sets the Windows CWD to a special
+directory in this case. This special directory points to a virtual
+filesystem within the native NT namespace (<filename>\??\PIPE\</filename>).
+Since it's not a real filesystem, the deliberate effect is that a call to,
+for instance, <function>CreateFile ("foo", ...);</function> will fail,
+as long as the processes CWD doesn't work as Windows CWD.</para>
+
+<para>So, in general, don't use the Win32 file API in Cygwin applications.
+If you <emphasis role='bold'>really</emphasis> need to access files using
+the Win32 API, or if you <emphasis role='bold'>really</emphasis> have to use
+<function>CreateProcess</function> to start applications, rather than
+the POSIX <function>exec(3)</function> family of functions, you have to
+make sure that the Cygwin CWD is set to some directory which is valid as
+Win32 CWD.</para>
+
</sect2>
<sect2 id="pathnames-additional"><title>Additional Path-related Information</title>
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