What is the posix_memalign() equivalent for the PostgreSQL?

Dear all,

I am developing an extension for the PostgreSQL that write/read some
external files from the PostgreSQL. In order to write/read, I am using the
O_DIRECT flag and using the posix_memalign to allocate memory. I would like
to know if the postgresql internal library provides an equivalent function
for the posix_memalign since I am getting unexpected errors. All my
allocations are in the TopMemoryContext since I am working with several
buffers that must be alive while the PostgreSQL Server is activated.

Thanks in advance,
Anderson