[PATCH v2] MdePkg BaseLib: API PathRemoveLastItem not handle root paths properly

[Hao Wu <hao.a.wu@intel.com>]

https://bugzilla.tianocore.org/show_bug.cgi?id=239

When the input path for API PathRemoveLastItem() is a root path like
'fs0:\', the API will return TRUE (indicating a directory or file was
removed from the path) and modifies the path to 'fs0:'. In fact, there's
no directory or file removed in the above case.

This commit adds additional check to resolve this issue and modifies the
API's description to make it more straightforward.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
---
 MdePkg/Include/Library/BaseLib.h   | 3 +--
 MdePkg/Library/BaseLib/FilePaths.c | 9 +++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
index 6268e6f..b69c703 100644
--- a/MdePkg/Include/Library/BaseLib.h
+++ b/MdePkg/Include/Library/BaseLib.h
@@ -1747,8 +1747,7 @@ BcdToDecimal8 (
 //
 
 /**
-  Removes the last directory or file entry in a path by changing the last
-  L'\' to a CHAR_NULL.
+  Removes the last directory or file entry in a path.
 
   @param[in, out] Path    The pointer to the path to modify.
 
diff --git a/MdePkg/Library/BaseLib/FilePaths.c b/MdePkg/Library/BaseLib/FilePaths.c
index 183b323..29a84ea 100644
--- a/MdePkg/Library/BaseLib/FilePaths.c
+++ b/MdePkg/Library/BaseLib/FilePaths.c
@@ -14,9 +14,8 @@
 #include  <Library/BaseLib.h>
 
 /**
-  Removes the last directory or file entry in a path by changing the last
-  L'\' to a CHAR_NULL. For a path which is like L"fs0:startup.nsh",
-  it's converted to L"fs0:".
+  Removes the last directory or file entry in a path. For a path which is
+  like L"fs0:startup.nsh", it's converted to L"fs0:".
 
   @param[in,out] Path     A pointer to the path to modify.
 
@@ -38,7 +37,9 @@ PathRemoveLastItem(
       ; Walker != NULL && *Walker != CHAR_NULL
       ; Walker++
      ){
-    if ((*Walker == L'\\' || *Walker == L':') && *(Walker + 1) != CHAR_NULL) {
+    if (*Walker == L'\\' && *(Walker + 1) != CHAR_NULL) {
+      LastSlash = Walker+1;
+    } else if (*Walker == L':' && *(Walker + 1) != L'\\' && *(Walker + 1) != CHAR_NULL) {
       LastSlash = Walker+1;
     }
   }
-- 
1.9.5.msysgit.0