MdePkg/UefiLib: don't special-case EFI_FILE_MODE_CREATE in OpenMode

While reviewing the patch that would land as 768b611136
("MdePkg/UefiLib: introduce EfiOpenFileByDevicePath()", 2018-08-16), Ray
pointed out that distinguishing EFI_FILE_MODE_CREATE was wasteful. Per
spec, if the file to create exists, then EFI_FILE_MODE_CREATE is ignored
by EFI_FILE_PROTOCOL.Open(), and the existent file is opened.

Therefore we don't need an attempt to "open-but-not-create" first, and a
fallback to "open-and-create-too" second -- that behavior is internal to
EFI_FILE_PROTOCOL.Open(). Remove the special-casing of
EFI_FILE_MODE_CREATE.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Suggested-by: Ruiyu Ni <ruiyu.ni@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1074
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Include/Library/UefiLib.h

@@ -1533,12 +1533,7 @@ EfiLocateProtocolBuffer (
 
   On the remaining device path, the longest initial sequence of
   FILEPATH_DEVICE_PATH nodes is node-wise traversed with
-  EFI_FILE_PROTOCOL.Open(). For the pathname fragment specified by each
+  EFI_FILE_PROTOCOL.Open().
-  traversed FILEPATH_DEVICE_PATH node, EfiOpenFileByDevicePath() first masks
-  EFI_FILE_MODE_CREATE out of OpenMode, and passes 0 for Attributes. If
-  EFI_FILE_PROTOCOL.Open() fails, and OpenMode includes EFI_FILE_MODE_CREATE,
-  then the operation is retried with the caller's OpenMode and Attributes
-  unmodified.
 
   (As a consequence, if OpenMode includes EFI_FILE_MODE_CREATE, and Attributes
   includes EFI_FILE_DIRECTORY, and each FILEPATH_DEVICE_PATH specifies a single
@@ -1570,18 +1565,10 @@ EfiLocateProtocolBuffer (
                            the last node in FilePath.
 
   @param[in] OpenMode      The OpenMode parameter to pass to
-                           EFI_FILE_PROTOCOL.Open(). For each
+                           EFI_FILE_PROTOCOL.Open().
-                           FILEPATH_DEVICE_PATH node in FilePath,
-                           EfiOpenFileByDevicePath() first opens the specified
-                           pathname fragment with EFI_FILE_MODE_CREATE masked
-                           out of OpenMode and with Attributes set to 0, and
-                           only retries the operation with EFI_FILE_MODE_CREATE
-                           unmasked and Attributes propagated if the first open
-                           attempt fails.
 
   @param[in] Attributes    The Attributes parameter to pass to
-                           EFI_FILE_PROTOCOL.Open(), when EFI_FILE_MODE_CREATE
+                           EFI_FILE_PROTOCOL.Open().
-                           is propagated unmasked in OpenMode.
 
   @retval EFI_SUCCESS            The file or directory has been opened or
                                  created.

MdePkg/Library/UefiLib/UefiLib.c

@@ -1730,12 +1730,7 @@ EfiLocateProtocolBuffer (
 
   On the remaining device path, the longest initial sequence of
   FILEPATH_DEVICE_PATH nodes is node-wise traversed with
-  EFI_FILE_PROTOCOL.Open(). For the pathname fragment specified by each
+  EFI_FILE_PROTOCOL.Open().
-  traversed FILEPATH_DEVICE_PATH node, EfiOpenFileByDevicePath() first masks
-  EFI_FILE_MODE_CREATE out of OpenMode, and passes 0 for Attributes. If
-  EFI_FILE_PROTOCOL.Open() fails, and OpenMode includes EFI_FILE_MODE_CREATE,
-  then the operation is retried with the caller's OpenMode and Attributes
-  unmodified.
 
   (As a consequence, if OpenMode includes EFI_FILE_MODE_CREATE, and Attributes
   includes EFI_FILE_DIRECTORY, and each FILEPATH_DEVICE_PATH specifies a single
@@ -1767,18 +1762,10 @@ EfiLocateProtocolBuffer (
                            the last node in FilePath.
 
   @param[in] OpenMode      The OpenMode parameter to pass to
-                           EFI_FILE_PROTOCOL.Open(). For each
+                           EFI_FILE_PROTOCOL.Open().
-                           FILEPATH_DEVICE_PATH node in FilePath,
-                           EfiOpenFileByDevicePath() first opens the specified
-                           pathname fragment with EFI_FILE_MODE_CREATE masked
-                           out of OpenMode and with Attributes set to 0, and
-                           only retries the operation with EFI_FILE_MODE_CREATE
-                           unmasked and Attributes propagated if the first open
-                           attempt fails.
 
   @param[in] Attributes    The Attributes parameter to pass to
-                           EFI_FILE_PROTOCOL.Open(), when EFI_FILE_MODE_CREATE
+                           EFI_FILE_PROTOCOL.Open().
-                           is propagated unmasked in OpenMode.
 
   @retval EFI_SUCCESS            The file or directory has been opened or
                                  created.
@@ -1889,31 +1876,16 @@ EfiOpenFileByDevicePath (
     }
 
     //
-    // Open the next pathname fragment with EFI_FILE_MODE_CREATE masked out and
+    // Open or create the file corresponding to the next pathname fragment.
-    // with Attributes set to 0.
     //
     Status = LastFile->Open (
                          LastFile,
                          &NextFile,
                          PathName,
-                         OpenMode & ~(UINT64)EFI_FILE_MODE_CREATE,
+                         OpenMode,
-                         0
+                         Attributes
                          );
 
-    //
-    // Retry with EFI_FILE_MODE_CREATE and the original Attributes if the first
-    // attempt failed, and the caller specified EFI_FILE_MODE_CREATE.
-    //
-    if (EFI_ERROR (Status) && (OpenMode & EFI_FILE_MODE_CREATE) != 0) {
-      Status = LastFile->Open (
-                           LastFile,
-                           &NextFile,
-                           PathName,
-                           OpenMode,
-                           Attributes
-                           );
-    }
-
     //
     // Release any AlignedPathName on both error and success paths; PathName is
     // no longer needed.