Re: vfat lost file problem

[Paul Eggert]

Jim Meyering <address@hidden> writes:

> I believe something similar happens with file names
> that are too long.

On POSIX hosts, that can happen only if the file names are silently
truncated, right?  I.e., if _POSIX_NO_TRUNC is zero.  Does anybody
still use hosts like that?  If so, here's a patch.  This patch won't
fix any Debian behavior, since _POSIX_NO_TRUNC is 1 on Debian, but it
would help on _POSIX_NO_TRUNC==0 hosts.

Perhaps a similar patch could be used for vfat filesystems.  That is,
same_name could inspect the results of the stat system calls to see
whether the files live on a vfat filesystem.  I don't know all the ins
and outs of vfat names, though.

2003-08-17  Paul Eggert  <address@hidden>

        * same.c: Include <stdbool.h>, <limits.h>.
        (_POSIX_NAME_MAX): Define if not defined.
        (MIN): New macro.
        (same_name): If file names are silently truncated, report
        that the file names are the same if they are the same after
        the silent truncation.

--- same.c.~1.10.~      Tue Jan 14 07:07:24 2003
+++ same.c      Sun Aug 17 23:38:49 2003
@@ -21,6 +21,7 @@
 # include <config.h>
 #endif
 
+#include <stdbool.h>
 #include <stdio.h>
 #ifdef HAVE_UNISTD_H
 # include <unistd.h>
@@ -42,6 +43,11 @@ extern int errno;
 # include <strings.h>
 #endif
 
+#include <limits.h>
+#ifndef _POSIX_NAME_MAX
+# define _POSIX_NAME_MAX 14
+#endif
+
 #include "same.h"
 #include "dirname.h"
 #include "error.h"
@@ -54,6 +60,8 @@ extern int errno;
 void free ();
 #endif
 
+#define MIN(a, b) ((a) < (b) ? (a) : (b))
+
 #define SAME_INODE(Stat_buf_1, Stat_buf_2) \
   ((Stat_buf_1).st_ino == (Stat_buf_2).st_ino \
    && (Stat_buf_1).st_dev == (Stat_buf_2).st_dev)
@@ -69,9 +77,24 @@ same_name (const char *source, const cha
   char const *dest_basename = base_name (dest);
   size_t source_baselen = base_len (source_basename);
   size_t dest_baselen = base_len (dest_basename);
+  bool identical_basenames =
+    (source_baselen == dest_baselen
+     && memcmp (source_basename, dest_basename, dest_baselen) == 0);
+  bool compare_dirs = identical_basenames;
+  bool same = false;
+
+#if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
+  /* This implementation silently truncates pathname components.  If
+     the base names might be truncated, check whether the truncated
+     base names are the same, while checking the directories.  */
+  size_t slen_max = HAVE_LONG_FILE_NAMES ? 255 : _POSIX_NAME_MAX;
+  size_t min_baselen = MIN (source_baselen, dest_baselen);
+  if (slen_max <= min_baselen
+      && memcmp (source_basename, dest_basename, slen_max) == 0)
+    compare_dirs = true;
+#endif
 
-  if (source_baselen == dest_baselen
-      && memcmp (source_basename, dest_basename, dest_baselen) == 0)
+  if (compare_dirs)
     {
       struct stat source_dir_stats;
       struct stat dest_dir_stats;
@@ -93,12 +116,30 @@ same_name (const char *source, const cha
          error (1, errno, "%s", dest_dirname);
        }
 
+      same = SAME_INODE (source_dir_stats, dest_dir_stats);
+
+#if ! _POSIX_NO_TRUNC && HAVE_PATHCONF && defined _PC_NAME_MAX
+      if (same && ! identical_basenames)
+       {
+         long name_max = (errno = 0, pathconf (source_dirname, _PC_NAME_MAX));
+         if (name_max < 0)
+           {
+             if (errno)
+               {
+                 /* Shouldn't happen.  */
+                 error (1, errno, "%s", source_dirname);
+               }
+             same = false;
+           }
+         else
+           same = (name_max <= min_baselen
+                   && memcmp (source_basename, dest_basename, name_max) == 0);
+       }
+#endif
+
       free (source_dirname);
       free (dest_dirname);
-
-      if (SAME_INODE (source_dir_stats, dest_dir_stats))
-       return 1;
     }
 
-  return 0;
+  return same;
 }