document risks due to truncation of strings

doc/source/index.rst

@@ -14,6 +14,7 @@ Welcome to Wi4MPI's documentation!
    tutorial
    developer_guide
    generator_guide
+   limitations
 
 Indices and tables
 ==================

doc/source/limitations.rst

@@ -0,0 +1,30 @@
+Known limitations
+*****************
+
+MPI_MAX_* constants for strings size
+====================================
+
+MPI defines constants for the maximum length of some strings. Since their values can be different between the application side and the runtime side, truncation might happen.
+
+This could provoke issues with some routines because the strings might have different values between what the application sees and what the runtime expects.
+
+MPI_MAX_PORT_NAME
+-----------------
+
+Because port names are given by the runtime, if truncation happens the application will get a string that won't be usable in functions expecting a port name.
+
+MPI_MAX_INFO_KEY
+----------------
+
+Since key-value pairs in an MPI_Info object have a maximum length, truncation of the key might happen when setting one. Thus you could have an MPI_Info object with unexpected behaviour.
+
+MPI_MAX_INFO_VAL
+----------------
+
+The MPI standard discourage the allocation of a string with this size, allowing it to be very big. Thus we defer to the runtime the size check.
+It means that a value might not be accepted when setting it, even if the application checked that it is less than MPI_MAX_INFO_VAL.
+
+Other constants
+---------------
+
+Since other constants are either for information (type, window and communicator's name, processor name and library version string) or with only a portable subset (datarep of file views), their truncation is less at risk of provoking issues in their uses.