Bug 52037 w/ w95osr2 and beyond you can get freediskspace for a full path (eg UNC Paths).

The code will use the Ex API if available.
With this change the function should get the correct freespace numbers for submounts and junction points (introduced in w2k).

r=dougt sr=dveditz

xpcom/io/nsLocalFileWin.cpp

@@ -1510,16 +1510,10 @@ nsLocalFile::GetDiskSpaceAvailable(PRInt64 *aDiskSpaceAvailable)
     
     ResolveAndStat(PR_FALSE);
     
-    const char *filePath = mResolvedPath.get();
-
     PRInt64 int64;
     
     LL_I2L(int64 , LONG_MAX);
 
-    char aDrive[_MAX_DRIVE + 2];
-	_splitpath( (const char*)filePath, aDrive, NULL, NULL, NULL);
-	strcat(aDrive, "\\");
-
     // Check disk space
     DWORD dwSecPerClus, dwBytesPerSec, dwFreeClus, dwTotalClus;
     ULARGE_INTEGER liFreeBytesAvailableToCaller, liTotalNumberOfBytes, liTotalNumberOfFreeBytes;
@@ -1542,18 +1536,23 @@ nsLocalFile::GetDiskSpaceAvailable(PRInt64 *aDiskSpaceAvailable)
         FreeLibrary(hInst);
     }
 
-    if (getDiskFreeSpaceExA && (*getDiskFreeSpaceExA)(aDrive,
+    if (getDiskFreeSpaceExA && (*getDiskFreeSpaceExA)(mResolvedPath.get(),
                                                       &liFreeBytesAvailableToCaller, 
                                                       &liTotalNumberOfBytes,  
                                                       &liTotalNumberOfFreeBytes))
     {
         nBytes = (double)(signed __int64)liFreeBytesAvailableToCaller.QuadPart;
     }
-    else if ( GetDiskFreeSpace(aDrive, &dwSecPerClus, &dwBytesPerSec, &dwFreeClus, &dwTotalClus))
-    {
-        nBytes = (double)dwFreeClus*(double)dwSecPerClus*(double) dwBytesPerSec;
-    }
+    else {
+        char aDrive[_MAX_DRIVE + 2];
+        _splitpath( mResolvedPath.get(), aDrive, NULL, NULL, NULL);
+        strcat(aDrive, "\\");
 
+        if ( GetDiskFreeSpace(aDrive, &dwSecPerClus, &dwBytesPerSec, &dwFreeClus, &dwTotalClus))
+        {
+            nBytes = (double)dwFreeClus*(double)dwSecPerClus*(double) dwBytesPerSec;
+        }
+    }
     LL_D2L(*aDiskSpaceAvailable, nBytes);
 
     return NS_OK;