On Tue, Jan 29, 2008 at 01:27:57PM +0100, Jim Meyering wrote:
> Rogier Wolff <[EMAIL PROTECTED]> wrote:
> ...
> > Let me reiterate: It is the first "dd" that is misbehaving, when it
> > recieves a write error and SIGPIPE, it simply exits instead of
> > reporting the stats.
>
> Thanks for the report, but that behavior is required by POSIX.
> dd must handle SIGINT the way you want, but dd may not handle
> SIGPIPE that way:
>
> ASYNCHRONOUS EVENTS
>
> For SIGINT, the dd utility shall interrupt its current processing,
> write status information to standard error, and exit as though
> terminated by SIGINT. It shall take the standard action for all
> other signals; see the ASYNCHRONOUS EVENTS section in Section 1.4
> (on page 2280).
Please interpret it as dd is supposed to work:
Please block the "SIGPIPE" signal, then write will return:
EPIPE fd is connected to a pipe or socket whose reading end is
closed. When this happens the writing process will also
receive a SIGPIPE signal. (Thus, the write return
value is seen only if the program catches, blocks or
ignores this signal.)
then the write will return EPIPE, which is a normal error code,
indicating that writing has stopped, and that stats should be printed.
What is dd's "purpose in life"? Device-to-device copy, as it's name
suggests? Turns out modern use is often no longer device-to-device. It
copies files, and counts and reports the number of blocks copied. This
feature is used by some. If you go and change it, things will stop
working.
If you start "waving standards around", I'll bounce it back for
you. SIGPIPE is NOT an asynchronous event. As documented in the quoted
documentation for write. It happens synchronously with the write,
normally before the return of "EPIPE".
Roger.
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