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From:	"Wiktor S. (wswiktorSP AT Mpoczta DOT fm) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	a patch for LFN on exFAT
Date:	Sat, 14 May 2016 19:24:45 +0200
Organization:	INTERIA.PL S.A.
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

This patch fixes fopen() with LFN on filesystems that do not have short 
aliases for long names, like exFAT.

I have rebuild textutils with this patch, and now cat works properly:

=============

C:\>cat g:\longdirectoryname\longfilename.txt
c:/djtest/bin/cat.exe: g:\longdirectoryname\longfilename.txt: Permission 
denied (EACCES)


C:\>djtest\gnu\txtutil2.0\src\cat g:\longdirectoryname\longfilename.txt
It works.

=============

However, it is still not possible to do system("longfilename.exe") or 
system("longpathname\short.exe") on exFAT.
I don't know if it is possible to execute a program using its long name 
only.

=============

ffa8b583c4a1e552b5a9582a81b0785bf78199ee
 _open.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/_open.c b/_open.c
index 61d5b1a..18bde56 100644
--- a/_open.c
+++ b/_open.c
@@ -1,3 +1,4 @@
+/* Copyright (C) 2016 DJ Delorie, see COPYING.DJ for details */
 /* Copyright (C) 2014 DJ Delorie, see COPYING.DJ for details */
 /* Copyright (C) 2011 DJ Delorie, see COPYING.DJ for details */
 /* Copyright (C) 2002 DJ Delorie, see COPYING.DJ for details */
@@ -17,12 +18,17 @@
 #include <sys/fsext.h>
 #include <libc/fsexthlp.h>

+typedef enum {
+  false = 0, true = 1
+} bool;
+
 int
 _open(const char* filename, int oflag)
 {
   __dpmi_regs r;
   int rv;
   int use_lfn = _USE_LFN;
+  bool retry_with_lfn = false;

   if (filename == 0)
   {
@@ -50,6 +56,7 @@ _open(const char* filename, int oflag)
     __dpmi_int(0x21, &r);
     if (!(r.x.flags & 1))  /* Get short name success */
     {
+      retry_with_lfn = true;
       r.x.ax = 0x6c00;
       r.x.bx = (oflag & 0xff);
       r.x.dx = 1;   /* Open existing file */
@@ -83,6 +90,7 @@ _open(const char* filename, int oflag)
       }
     }
   }
+fallback:
   if (use_lfn)
   {
     r.x.flags = 1;  /* Always set CF before calling a 0x71NN function. */
@@ -136,6 +144,14 @@ do_open:
   }
   else if (r.x.flags & 1)
   {
+    if ((r.x.ax == 2 || r.x.ax == 3) && retry_with_lfn)
+    {
+      /* On exFAT partitions files and paths with long names do not have 
8.3
+         aliases. If an attempt to open the file with short name failed 
with
+         "file not found" or "path not found", retry with LFN API. */
+      retry_with_lfn = false;
+      goto fallback;
+    }
     errno = __doserr_to_errno(r.x.ax);
     return -1;
   }

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