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Update of fhandler-tut.txt

When trying to add an experimental /dev/mixer, I found that
the fhandler tutorial was obsolete. This patch brings it up-to-date.

ChangeLog Entry:

2004-11-28  Gerd Spalink  <>

        * fhandler-tut.txt: Update description to cygwin 1.5.13


Index: fhandler-tut.txt
RCS file: /cvs/src/src/winsup/doc/fhandler-tut.txt,v
retrieving revision 1.2
diff -p -u -r1.2 fhandler-tut.txt
--- fhandler-tut.txt    18 Aug 2000 19:52:31 -0000      1.2
+++ fhandler-tut.txt    28 Nov 2004 18:38:47 -0000
@@ -6,7 +6,7 @@ showing an example of /dev/zero.
 Files to note:

 fhandler.h - must define a new derived class here and FH_* - to notice "/dev/zero" and mark it - to notice "/dev/zero" and mark it - new - to create the fhandler instance

@@ -27,23 +27,38 @@ simulating everything.  Thus:
   handle of -1, which (1) maps swap memory, and (2) zeros it out for
   us (at least, on NT).

-OK, let's start with fhandler.h.
+OK, let's start with devices.h.

-First, update the comment about which files are where.  We're adding
-fhandler_dev_zero as FH_DEV_ZERO.  We're adding this as a "fast"
-device (it will never block) so we have to adjust FH_NDEV also.
+We have to create a new entry in the enum fh_devices.  The new
+devices must get a major and a minor ID.  As a rule of thumb, just
+copy the ones that are used on a linux system.

-Later in that file, we'll copy fhandler_dev_null and edit it to be
+Now, let's continue with fhandler.h.
+First, update the fhandler_union near the end of the file with a
+line for the new device.  Use existing members, in this case __dev_null
+as a template.  This union is sorted alphabetically.
+Earlier in that file, we'll copy fhandler_dev_null and edit it to be
 fhandler_dev_zero.  I chose that one because it's small, but we'll add
 more members as we go (since we're simulating the whole thing).  In
 fact, let's copy the I/O methods from fhandler_windows since we'll
 need all those anyway, even though we'll go through the full list

-OK, next we need to edit to recognize when the user is trying
-to open "/dev/zero".  Look in get_device_number; there's a long list
-of cases, just add one (I added one after "null").  Also remember to
-add an entry to the windows_device_names list in the right spot.
+OK, next we need to edit  There is a section where each device
+is listed with its cygwin path, its structure and its windows path.
+"/dev/zero", FH_ZERO, "\\dev\\zero"
+This is needed to recognize when the user is trying to open "/dev/zero".
+You have to build from now.
+There is a script 'gendevices' in the winsup/cygwin directory which may
+be called at some time in the future if you use 'make' to build the DLL.
+However, I had to type
+make /cygdrive/c/sw/cygwin_dev/src/winsup/cygwin/
+in the directory /cygdrive/c/sw/cygwin_dev/obj/i686-pc-cygwin/winsup/cygwin
+to achieve this.  Note the absolute path names here.
+You have to have shilka available to do that; this is part of the
+cygwin cocom package.

 To go along with that change, we'll need to change  Look for
 FH_NULL and add a case for FH_ZERO as well.

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