Add ability to reverse byte order of partition names to gdisk and sgdisk

8 files changed, 66 insertions, 4 deletions

diff --git a/NEWS b/NEWS
index 023e1d1..bd6696c 100644
--- a/NEWS
+++ b/NEWS
@@ -1,11 +1,20 @@
 1.0.8 (?/??/2021):
 ------------------
 
-- Fixed double byte swap operation on writes of partition label data on
+- Fixed double byte swap operation on writes of partition name data on
   big-endian systems; this is in addition to the double byte swap fix on
   reading partition label data fixed in 1.0.7. (Thanks to Erik Larsson for
   both fixes.)
 
+- Added feature to gdisk and sgdisk to enable swapping the byte order of
+  partition names, so as to correct disks already affected by the preceding
+  bug. This option is 'b' on the experts' menu in gdisk and
+  -b/--byte-swap-name in sgdisk. This seems advanced/obscure enough that I
+  don't want to clutter cgdisk's menu with this option, so I haven't added
+  it there.
+
+- Trivial code cleanup.
+
 1.0.7 (3/10/2021):
 ------------------
 
diff --git a/gdisk.8 b/gdisk.8
index 85b69cb..7f7a949 100644
--- a/gdisk.8
+++ b/gdisk.8
@@ -420,6 +420,14 @@ aren't translated into anything useful. In practice, most OSes seem to
 ignore these attributes.
 
 .TP 
+.B b
+Swap the byte order for the name of the specified partition. Some
+partitioning tools, including GPT fdisk 1.0.7 and earlier, can write the
+partition name in the wrong byte order on big-endian computers, such as the
+IBM s390 mainframes and PowerPC-based Macs. This feature corrects this
+problem.
+
+.TP 
 .B c
 Change partition GUID. You can enter a custom unique GUID for a partition
 using this option. (Note this refers to the GUID that uniquely identifies a
diff --git a/gptcl.cc b/gptcl.cc
index 2304091..65a99e9 100644
--- a/gptcl.cc
+++ b/gptcl.cc
@@ -64,6 +64,7 @@ int GPTDataCL::DoOptions(int argc, char* argv[]) {
    GPTData secondDevice;
    int opt, numOptions = 0, saveData = 0, neverSaveData = 0;
    int partNum = 0, newPartNum = -1, saveNonGPT = 1, retval = 0, pretend = 0;
+   int byteSwapPartNum = 0;
    uint64_t low, high, startSector, endSector, sSize, mainTableLBA;
    uint64_t temp; // temporary variable; free to use in any case
    char *device;
@@ -76,6 +77,7 @@ int GPTDataCL::DoOptions(int argc, char* argv[]) {
           "list|[partnum:show|or|nand|xor|=|set|clear|toggle|get[:bitnum|hexbitmask]]"},
       {"set-alignment", 'a', POPT_ARG_INT, &alignment, 'a', "set sector alignment", "value"},
       {"backup", 'b', POPT_ARG_STRING, &backupFile, 'b', "backup GPT to file", "file"},
+      {"byte-swap-name", 'B',  POPT_ARG_INT, &byteSwapPartNum, 'B', "byte-swap partition's name", "partnum"},
       {"change-name", 'c', POPT_ARG_STRING, &partName, 'c', "change partition's name", "partnum:name"},
       {"recompute-chs", 'C', POPT_ARG_NONE, NULL, 'C', "recompute CHS values in protective/hybrid MBR", ""},
       {"delete", 'd', POPT_ARG_INT, &deletePartNum, 'd', "delete a partition", "partnum"},
@@ -191,6 +193,15 @@ int GPTDataCL::DoOptions(int argc, char* argv[]) {
                case 'a':
                   SetAlignment(alignment);
                   break;
+               case 'B':
+                  if (IsUsedPartNum(byteSwapPartNum - 1)) {
+                     partitions[byteSwapPartNum - 1].ReverseNameBytes();
+                     cout << "Changed partition " << byteSwapPartNum << "'s name to "
+                          << partitions[byteSwapPartNum - 1].GetDescription() << "\n";
+                     JustLooking(0);
+                     saveData = 1;
+                  }
+                  break;
                case 'b':
                   SaveGPTBackup(backupFile);
                   free(backupFile);
diff --git a/gptpart.cc b/gptpart.cc
index 841140a..b83254d 100644
--- a/gptpart.cc
+++ b/gptpart.cc
@@ -412,14 +412,18 @@ int GPTPart::DoTheyOverlap(const GPTPart & other) {
 // Reverse the bytes of integral data types and of the UTF-16LE name;
 // used on big-endian systems.
 void GPTPart::ReversePartBytes(void) {
-   int i;
-
    ReverseBytes(&firstLBA, 8);
    ReverseBytes(&lastLBA, 8);
    ReverseBytes(&attributes, 8);
+   ReverseNameBytes();
+} // GPTPart::ReversePartBytes()
+
+void GPTPart::ReverseNameBytes(void) {
+   int i;
+
    for (i = 0; i < NAME_SIZE; i ++ )
       ReverseBytes(name + i, 2);
-} // GPTPart::ReversePartBytes()
+} // GPTPart::ReverseNameBytes()
 
 /****************************************
  * Functions requiring user interaction *
diff --git a/gptpart.h b/gptpart.h
index fac514e..51bfb38 100644
--- a/gptpart.h
+++ b/gptpart.h
@@ -94,6 +94,7 @@ class GPTPart {
       void BlankPartition(void); // empty partition of data
       int DoTheyOverlap(const GPTPart & other); // returns 1 if there's overlap
       void ReversePartBytes(void); // reverse byte order of all integer fields
+      void ReverseNameBytes(void); // reverse byte order of partition's name field
 
       // Functions requiring user interaction
       void ChangeType(void); // Change the type code
diff --git a/gpttext.cc b/gpttext.cc
index 505f006..b1d9361 100644
--- a/gpttext.cc
+++ b/gpttext.cc
@@ -341,6 +341,22 @@ int GPTDataTextUI::SetName(uint32_t partNum) {
    return retval;
 } // GPTDataTextUI::SetName()
 
+// Enable the user to byte-swap the name of the partition. Used to correct
+// partition names damaged by incorrect byte order, as could be created by
+// GPT fdisk 1.0.7 and earlier on big-endian systems, and perhaps other tools.
+void GPTDataTextUI::ReverseName(uint32_t partNum) {
+   int swapBytes;
+
+   cout << "Current name is: " << partitions[partNum].GetDescription() << "\n";
+   partitions[partNum].ReverseNameBytes();
+   cout << "Byte-swapped name is: " << partitions[partNum].GetDescription() << "\n";
+   cout << "Do you want to byte-swap the name? ";
+   swapBytes = (GetYN() == 'Y');
+   // Already swapped for display, so undo if necessary....
+   if (!swapBytes)
+      partitions[partNum].ReverseNameBytes();
+} // GPTDataTextUI::ReverseName()
+
 // Ask user for two partition numbers and swap them in the table. Note that
 // this just reorders table entries; it doesn't adjust partition layout on
 // the disk.
@@ -799,6 +815,9 @@ void GPTDataTextUI::ExpertsMenu(string filename) {
             else
                cout << "No partitions\n";
             break;
+         case 'b': case 'B':
+            ReverseName(GetPartNum());
+            break;
          case 'c': case 'C':
             ChangeUniqueGuid();
             break;
@@ -896,6 +915,7 @@ void GPTDataTextUI::ExpertsMenu(string filename) {
 
 void GPTDataTextUI::ShowExpertCommands(void) {
    cout << "a\tset attributes\n";
+   cout << "b\tbyte-swap a partition's name\n";
    cout << "c\tchange partition GUID\n";
    cout << "d\tdisplay the sector alignment value\n";
    cout << "e\trelocate backup data structures to the end of the disk\n";
diff --git a/gpttext.h b/gpttext.h
index afe4651..6bd22cf 100644
--- a/gpttext.h
+++ b/gpttext.h
@@ -49,6 +49,7 @@ class GPTDataTextUI : public GPTData {
       void ChangeUniqueGuid(void);
       void SetAttributes(uint32_t partNum);
       int SetName(uint32_t partNum);
+      void ReverseName(uint32_t partNum);
       int SwapPartitions(void);
       int DestroyGPTwPrompt(void); // Returns 1 if user proceeds
       void ShowDetails(void);
diff --git a/sgdisk.8 b/sgdisk.8
index ec1243d..ca2eb21 100644
--- a/sgdisk.8
+++ b/sgdisk.8
@@ -183,6 +183,14 @@ the backup may not accurately reflect the damaged state; instead, they
 will reflect GPT fdisk's first\-pass interpretation of the GPT.
 
 .TP 
+.B \-B, \-\-byte\-swap\-name=partnum
+Swap the byte order for the name of the specified partition. Some
+partitioning tools, including GPT fdisk 1.0.7 and earlier, can write the
+partition name in the wrong byte order on big-endian computers, such as the
+IBM s390 mainframes and PowerPC-based Macs. This feature corrects this
+problem.
+
+.TP 
 .B \-c, \-\-change\-name=partnum:name
 Change the GPT name of a partition. This name is encoded as a UTF\-16
 string, but proper entry and display of anything beyond basic ASCII values