* winsup/cygwin/include/cygwin/version.h: Bump API minor version.

	* winsup/cygwin/include/cygwin/types.h: Define key_t as long long.
	* winsup/cygwin/cygwin.din: Add ftok, _ftok.
	* winsup/cygwin/ipc.cc (ftok): Rework implementation.

1 files changed, 65 insertions, 12 deletions

diff --git a/winsup/cygwin/ipc.cc b/winsup/cygwin/ipc.cc
index e4a36cb7f..d37f45947 100644
--- a/winsup/cygwin/ipc.cc
+++ b/winsup/cygwin/ipc.cc
@@ -1,8 +1,9 @@
 /* ipc.cc: Single unix specification IPC interface for Cygwin
 
-   Copyright 2001, 2002 Red Hat, Inc.
+   Copyright 2001, 2002, 2003 Red Hat, Inc.
 
    Originally written by Robert Collins <robert.collins@hotmail.com>
+   Updated to 64 bit key_t by Charles Wilson <cygwin@cwilson.fastmail.fm>
 
    This file is part of Cygwin.
 
@@ -14,26 +15,78 @@
 #include <cygwin/ipc.h>
 #include <sys/stat.h>
 
-extern "C"
-{
-
 /* Notes: we return a valid key even if id's low order 8 bits are 0. */
-key_t
+extern "C" key_t
 ftok (const char *path, int id)
 {
   struct __stat64 statbuf;
+  key_t tmp;
   if (stat64 (path, &statbuf))
     {
       /* stat set the appropriate errno for us */
       return (key_t) -1;
     }
 
-  /* dev_t is short for cygwin
-   * ino_t is long for cygwin
-   * and we need 8 bits for the id.
-   * thus key_t is long long.
-   */
-  return ((long long) statbuf.st_dev << (5*8)) | (statbuf.st_ino << (8) ) | (id & 0x00ff);
-}
+  /* Since __CYGWIN_USE_BIG_TYPES__,
+     dev_t is 32bits for cygwin
+     ino_t is 64bits for cygwin
+     and we need 8 bits for the id.
+     thus key_t needs 104 bits total -- but we only have 64 (long long)
+     We will have to alias; leaving open the possibility that the same
+     key will be returned for multiple files.  This possibility exists
+     also on Linux; the question is, how to minimize this possibility.
+    
+     How to solve?  Well, based on C. Vinschen's research, the nFileIndex*
+     words vary as follows, on a partition with > 110,000 files
+     nFileIndexHigh:    564 values between 0x00010000 -- 0xffff0000
+     nFileIndexLow : 103812 values between 0x00000000 -- 0x0003ffff
+     R. Collins suggests that these may represent a tree path, 
+     and that it would require ~2.9M files to force the tree depth
+     to increase and reveal more bit usage.
+    
+     Implementation details: dev_t is 32bits, but is formed by
+        device(32bits) << 16 | unit(32bits)
+     But device is ACTUALLY == status & FH_DEVMASK, where FH_DEVMASK
+     is 0x00000fff --> 12 bits
+    
+     As it happens, the maximum number of devices is actually 
+     FH_NDEV, not FH_DEVMASK, where FH_NDEV is currently 0x0000001d.
+     However, FH_NDEV grows as new device types are added.  So
+     currently the device number needs 5 bits, but later?  Let's
+     take a cue from Linux, and use the lower 8 bits (instead of the
+     lower 12 or 16) for the device (major?) number.
+    
+     Similarly, while 'units' is an int (32bits), it is unclear
+     how many of these are significant. For most devices, it seems that
+     'units' is equivalent to 'minor'.  For FH_TAPE, it's obvious that
+     only 8 bits are important.  However, for FH_SOCKET...it might be
+     as high as 16 significant bits.
+    
+     Let's assume that we only need 8 bits from device (major) and
+     only 8 bits from unit (minor). (On linux, only 8 bits of minor
+     are used, and none from major).
+     ---> so, we only need 0x00ff00ff (16 bits) of dev_t
+    
+     ---> we MUST have all 8 bits of id.
+    
+     ---> So, we only have 64 - 8 - 16 = 40 bits for ino_t.  But, we
+     need 0xffff0000 for nFileIndexHigh and 0x0003ffff for nFileIndexLow
+     minimum, or 16 + 18 = 34 bits.  Lucky us - we have 6 more bits
+     to distribute.
+    
+     For lack of a better idea, we'll allocate 2 of the extra bits to
+     nFileIndexHigh and 4 to nFileIndexLow.  */
 
+  /* get 8 bits from dev_t (major), put into 0xff00000000000000L */
+  tmp  = (((key_t) statbuf.st_dev) & 0x0000000000ff0000LL) << 40;
+  /* get 8 bits from dev_t (minor), put into 0x00ff000000000000L */
+  tmp |= (((key_t) statbuf.st_dev) & 0x00000000000000ffLL) << 48;
+  /* get upper 16+2 bits from nFileInfoHigh, put into 0x0000ffffc0000000L
+     shift down first, then mask, to avoid sign extension on rightshift  */
+  tmp |= (((key_t) statbuf.st_ino) & 0xffffc00000000000LL) >> 16;
+  /* get lower 18+4 bits from nFileInfoLow, put into  0x000000003fffff00L  */
+  tmp |= (((key_t) statbuf.st_ino) & 0x00000000003fffffLL) << 8;
+  /* use all 8 bits of id, and put into 0x00000000000000ffL */
+  tmp |= (id & 0x00ff);
+  return tmp;
 }