AC_DEFUN(MP_GET_BLKSIZE, [
    AC_MSG_CHECKING([file I/O block size])
    AC_CACHE_VAL(mp_cv_var_st_blksize, [
    >conftesttmp
    AC_TRY_RUN([
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#ifdef HAVE_UNISTD_H
# include <unistd.h>
#endif
main()
{
    struct stat statbuf;
    FILE *f;
    if (! (f = fopen("conftestval", "w")))
	exit(1);
    if (stat("conftesttmp", &statbuf) == -1)
	exit(1);
    fprintf(f, "%d", statbuf.st_blksize);
    exit(0);
}], [mp_cv_var_st_blksize=`cat conftestval`], [mp_cv_var_st_blksize=""])])
if test x"${mp_cv_var_st_blksize}" = x; then
    mp_cv_var_st_blksize=4096
    AC_MSG_RESULT([Couldn't get block size, setting it to 4096])
else
    AC_MSG_RESULT($mp_cv_var_st_blksize)
fi
])
.