What SQL type for SQLBindParameter for NVARCHAR(MAX)/NTEXT when using UTF-8 locale?

Hello,

I am using a UTF-8 encoding in my Linux FreeTDS client program,
and want to insert LOB data into NVARCHAR(MAX)/NTEXT columns.

For now, I bind the SQL Parameter with:

         ctype = SQL_C_CHAR;
         sqltype = SQL_LONGVARCHAR;
         precision = 0x10000000;

This works find as long as the data is ASCII (and probably also
ISO-885901), but when using UTF-8 sequences, I get this error:

SQL State: HY000
SQL code : 2402
[FreeTDS][SQL Server]Error converting characters into server's character set. Some character(s) could not be converted

I guess this is expected, because I use SQL_LONGVARCHAR...

For NCHAR/NVARCHAR types, I use SQL_WCHAR / SQL_WVARCHAR SQL types
to bind my UTF-8 buffers, and this works fine.

But for large objects, what SQL type should I use?

I tried with SQL_WVARCHAR and a large size, without success:

   [FreeTDS][SQL Server]Invalid string or buffer length

How to specify the precision for a CLOB?

As a comparison, with Easysoft SQL Server ODBC driver, you can bind
UTF-8 buffers with:

         ctype = SQL_C_CHAR;
         sqltype = SQL_WVARCHAR;
         precision = SQL_SS_LENGTH_UNLIMITED;

Thanks for reading, please let me know what I should use!

Seb