libc's struct Stat is defined incorrectly on 64-bit FreeBSD

[aidancully]

blksize_t on 64-bit FreeBSD is 32 bits, not 64.

#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stddef.h>

#define pr_field_offset(field) \
  do { printf(# field ": %d\n", offsetof(struct stat, field)); } while (0)

int main(int argc, char *argv[])
{
  printf("%d\n", sizeof(struct stat));
  pr_field_offset(st_dev);
  pr_field_offset(st_size);
  pr_field_offset(st_blocks);
  pr_field_offset(st_blksize);
  pr_field_offset(st_flags);
  pr_field_offset(st_gen);
  pr_field_offset(st_birthtim);
  return 0;
}

on FreeBSD x86_64 yields:

120
st_dev: 0
st_size: 72
st_blocks: 80
st_blksize: 88
st_flags: 92
st_gen: 96
st_birthtim: 104

#![feature(libc)]
extern crate libc;

macro_rules! containerof_field_offset {
    ($container:ty : $field:ident) => (unsafe {
        &(*(0usize as *const $container)).$field as *const _ as usize
    })
}
macro_rules! pr_field_offsets {
  ( $( $field:ident ),* ) => (unsafe {
    $(
      println!("{}: {}", stringify!($field), containerof_field_offset!(libc::stat : $field));
    )*
  })
}

fn main() {
  println!("{}", std::mem::size_of::<libc::stat>());
  pr_field_offsets!(st_dev, st_ino, st_mode, st_nlink, st_uid, st_gid, st_rdev, st_atime, st_atime_nsec);
  pr_field_offsets!(st_atime, st_atime_nsec, st_mtime, st_mtime_nsec, st_ctime, st_ctime_nsec);
  pr_field_offsets!(st_size, st_blocks, st_blksize, st_flags, st_gen, st_lspare, st_birthtime, st_birthtime_nsec);
  pr_field_offsets!(__unused);
}

yields:

$ ./test
136
st_dev: 0
st_ino: 4
st_mode: 8
st_nlink: 10
st_uid: 12
st_gid: 16
st_rdev: 20
st_atime: 24
st_atime_nsec: 32
st_atime: 24
st_atime_nsec: 32
st_mtime: 40
st_mtime_nsec: 48
st_ctime: 56
st_ctime_nsec: 64
st_size: 72
st_blocks: 80
st_blksize: 88
st_flags: 96
st_gen: 100
st_lspare: 104
st_birthtime: 112
st_birthtime_nsec: 120
__unused: 128

I tracked this down to the blksize_t type definition, which is unconditionally 32-bit on FreeBSD (see here, noting this line:

typedef __uint32_t      __blksize_t;    /* file block size */

this is unconditionally the definition of __blksize_t on FreeBSD - whether on 32-bit or 64-bit platform.)

[aidancully]

Also, __unused is a no-op (two fields of size 0) on 64-bit FreeBSD, the __unused field can be deleted from the structure.