[lldb] [Python] Do not attempt to flush() a read-only fd

[mgorny]

Summary

When creating a FileSP object, do not flush() the underlying file unless
it is open for writing. Attempting to flush() a read-only fd results
in EBADF on NetBSD.

[lawrence_danna]

LGTM

[mgorny]

Could you push this for me? It seems that I have missed the GitHub migration and I didn't get commit access to the new repository.

[lawrence_danna]

In D69320#1718288, @mgorny wrote:

Could you push this for me? It seems that I have missed the GitHub migration and I didn't get commit access to the new repository.

looks like i've got the same problem

[krytarowski]

Same here, I cannot commit.

[mgorny]

@labath, can you commit to the new repo by any chance? ;-)

lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp

llvm::Expected<FileSP> PythonFile::ConvertToFile(bool borrowed) {
   if (fd < 0) {
     PyErr_Clear();
     return ConvertToFileForcingUseOfScriptingIOMethods(borrowed);
   }
   auto options = GetOptionsForPyObject(*this);
   if (!options)
     return options.takeError();
 
+  if (options.get() & File::eOpenOptionWrite) {
     // LLDB and python will not share I/O buffers.  We should probably
     // flush the python buffers now.
     auto r = CallMethod("flush");
     if (!r)
       return r.takeError();
+  }
 
   FileSP file_sp;
   if (borrowed) {
     // In this case we we don't need to retain the python
     // object at all.
     file_sp = std::make_shared<NativeFile>(fd, options.get(), false);
   } else {
     file_sp = std::static_pointer_cast<File>(