Why does getpagesize() return an int?

Question

Why does the syscall getpagesize() return an int and not an unsigned int or a size_t?

Prototype and short description below:

GETPAGESIZE(2)                                                             
    NAME
           getpagesize - get memory page size
    SYNOPSIS
           #include <unistd.h>
           int getpagesize(void);

Answer 1

int was probably sufficient when it was invented. But it's no longer an issue because the getpagesize() has been removed from POSIX standard since 2001 and has been superseded by sysconf(). You should use sysconf(_SC_PAGESIZE).

getpagesize() returning an int was one of the major reasons why it was removed:

getpagesize

The getpagesize( ) function returns the current page size. It is equivalent to sysconf (_SC_PAGE_SIZE) and sysconf (_SC_PAGESIZE). This interface, returning an int, may have problems representing appropriate values in the future. Also the behaviour is not specified for this interface on systems that support variable size pages. On variable page size systems, a page can be extremely large (theoretically, up to the size of memory). This allows very efficient address translations for large segments of memory that have common page attributes. A note about this has been added to Application Usage, and the interface marked Legacy, with the recommendation that applications should use the sysconf() interface instead.

(emphasis mine).