No special actions are required. There are several important changes
in version 8.14, most notable ones being improved dkim_sign
function, DNS resolver tolerance for CNAME chains, and buffered I/O.
This change is important for those who use dkim_sign with
Sendmail. See dkim_sign and sendmail, for a detailed discussion.
Mailfromd dropped support for CNAME chains in version 8.3
(see 820-830). This change was forced by the behavior of
the adns resolver library, which had apparently been grounded
on somewhat rigorous reading of RFCs
103432
and
218133.
Reportedly, many existing DNS servers still employ CNAME chains leading to
TXT records (in particular, to DKIM TXT records), so this change made certain
DKIM signatures unverifiable for mailfromd.
To fix this, starting from version 8.14 mailfromd implements
a work-around that allows it to follow CNAME chains of limited
length. The default length is 2 (which means CNAME pointing to a
CNAME, pointing to a valid RR). It can be changed using the
dns.max-cname-chain configuration statement
(see conf-resolver).
Buffered I/O can tremendously improve performance of getdelim
and getline.
The global variables io_buffering and io_buffer_size
(see io_buffering) define buffering mode and associated buffer
size for file descriptors returned by the subsequent calls to
open or spawn. Buffering mode of an already open file
descriptor can be changed using the setbuf function.
The io_buffering variable defines the buffering mode. By
default it is 0 (BUFFER_NONE), which disables buffering for
backward compatibility with the previous versions. Another
possible values are: 1 (BUFFER_FULL) and 2 (BUFFER_LINE).
When set to BUFFER_FULL, all I/O operations become fully buffered.
The buffer size is defined by the io_buffer_size global variable.
BUFFER_LINE is similar to BUFFER_FILE when used for
input. When used for the output, the data are accumulated in buffer
and actually sent to the underlying transport stream when the newline
character is seen. The io_buffer_size global variable sets the
initial value for the buffer size in this mode. The actual size can
grow as needed during the I/O.
The default value for io_buffer_size is the size of the system page.
The symbolic constants BUFFER_NONE, BUFFER_FULL and
BUFFER_LINE are defined in the status.mf module. E.g.:
require status
begin
do
io_buffering = BUFFER_FULL
done
will set up all the subsequent buffer-aware I/O functions for buffered reads and writes using the maximum buffer capacity.
The setbuf function (see setbuf) changes the buffering
mode and/or buffer size for an already opened stream, e.g.:
setbuf(fd, BUFFER_FULL, 4096)
For detailed discussion of various buffering modes and their effect on the I/O, see I/O functions.