unix: Add PIPE_BUF for bsd and notbsd

This is the maximum size of guaranteed-atomic writes to a pipe.

Author: kamalmarhubi

src/unix/bsd/mod.rs

@@ -293,6 +293,8 @@ pub const WNOHANG: ::c_int = 1;
 pub const RTLD_NOW: ::c_int = 0x2;
 pub const RTLD_DEFAULT: *mut ::c_void = -2isize as *mut ::c_void;
 
+pub const PIPE_BUF: usize = 512;
+
 f! {
     pub fn FD_CLR(fd: ::c_int, set: *mut fd_set) -> () {
         let bits = mem::size_of_val(&(*set).fds_bits[0]) * 8;

src/unix/notbsd/mod.rs

@@ -645,6 +645,8 @@ pub const POSIX_FADV_NOREUSE: ::c_int = 5;
 pub const AT_FDCWD: ::c_int = -100;
 pub const AT_SYMLINK_NOFOLLOW: ::c_int = 0x100;
 
+pub const PIPE_BUF: usize = 4096;
+
 f! {
     pub fn FD_CLR(fd: ::c_int, set: *mut fd_set) -> () {
         let fd = fd as usize;