Cygwin: forkables: update doc, add release notes

3 files changed, 30 insertions, 11 deletions

diff --git a/winsup/cygwin/release/3.0 b/winsup/cygwin/release/3.0
index da0fe0961..da357558d 100644
--- a/winsup/cygwin/release/3.0
+++ b/winsup/cygwin/release/3.0
@@ -31,6 +31,12 @@ What's new:
 - New APIs: signalfd, timerfd_create, timerfd_gettime, timerfd_settime,
   timer_getoverrun.
 
+- fork(2) now is able to recover from when an in-use executable/dll is
+  removed or replaced during process runtime.  This feature is disabled by
+  default and limited to exes/dlls on the same NTFS partition as the Cygwin
+  installation.  For more information and how to enable, please refer to
+  https://www.cygwin.com/cygwin-ug-net/highlights.html#ov-hi-process
+
 
 What changed:
 -------------
diff --git a/winsup/doc/highlights.xml b/winsup/doc/highlights.xml
index 25b227382..67e326cb4 100644
--- a/winsup/doc/highlights.xml
+++ b/winsup/doc/highlights.xml
@@ -202,21 +202,27 @@ While Windows does not allow to remove binaries in use from the file
 system, they still can be renamed or moved into the recycle bin, as
 outlined for unlink(2) in <xref linkend="ov-new1.7-file"></xref>.
 To allow an existing process to fork, the original binary files need to be
-available via their original file names, but they may reside in
-different directories when using the <ulink
+available via their original file names, but they may reside in a
+different directory when using the <ulink
 url="https://social.msdn.microsoft.com/search/en-US?query=dotlocal%20dll%20redirection"
 >DotLocal (.local) Dll Redirection</ulink> feature.
 Since NTFS does support hardlinks, when the fork fails we try again, but
 create a private directory containing hardlinks to the original files as
-well as the .local file now.  The private directory for the hardlinks is
-/var/run/cygfork/, which you have to create manually for now if you need to
-protect fork against exe- and dll- updates on your Cygwin instance.  As
-hardlinks cannot be used across multiple NTFS file systems, please make sure
-your exe- and dll- replacing operations operate on the same single NTFS file
-system as your Cygwin instance and the /var/run/cygfork/ directory.</para>
-
-<para>We create one directory per user, application and application age,
-and remove it when no more processes use that directory.  To indicate
+well as the <literal>.local</literal> file now.  The base directory for the
+private hardlink directory is <literal>/var/run/cygfork/</literal>, which
+you have to create manually for now if you need to protect fork against
+updates to executables and dlls on your Cygwin instance.  As hardlinks
+cannot be used across multiple NTFS file systems, please make sure your
+executable and dll replacing operations operate on the same single NTFS file
+system as your Cygwin instance and the <literal>/var/run/cygfork/</literal>
+directory.  Note that this private hardlink directory also does help for
+when a wrong dll is found in the parent process' current working directory.
+To enable creating the hardlinks, you need to stop all currently running
+Cygwin processes after creating this directory, once per Cygwin installation:
+<literallayout>$ mkdir --mode=a=rwxt /var/run/cygfork</literallayout></para>
+
+<para>We create one hardlink directory per user, application and application
+age, and remove it when no more processes use that directory.  To indicate
 whether a directory still is in use, we define a mutex name similar to
 the directory name.  As mutexes are destroyed when no process holds a
 handle open any more, we can clean up even after power loss or similar:
diff --git a/winsup/doc/new-features.xml b/winsup/doc/new-features.xml
index 6801e3eeb..8fc0ac6fe 100644
--- a/winsup/doc/new-features.xml
+++ b/winsup/doc/new-features.xml
@@ -107,6 +107,13 @@ Native Windows processes not started by Cygwin processes are mapped
 into the range beyond 65535.
 </para></listitem>
 
+<listitem><para>
+fork(2) now is able to recover from when an in-use executable/dll is
+removed or replaced during process runtime.  This feature is disabled by
+default and limited to exes/dlls on the same NTFS partition as the Cygwin
+installation.  For more information and how to enable, please refer to
+<xref linkend="ov-hi-process"></xref>.
+</para></listitem>
 </itemizedlist>
 
 </sect2>