Defect in XCU 2.11

[Geoff Clare <yyy@xxxxxxxxxxxxx>]

@ page 61 line 2519-2521 section 2.11 objection [gwc shell bg sig]

Problem:

Defect code :  1. Error

Section 2.11 "Signals and Error Handling" says:

    "When a command is in an asynchronous list, the shell shall
    prevent SIGQUIT and SIGINT signals from the keyboard from
    interrupting the command."

Taken at face value this seems to be requiring rather more than
what current shells do, which is simply to arrange for the executed
command to inherit a signal action of SIG_IGN for those signals.

In particular, it requires that if the command resets SIGINT to
SIG_DFL the shell must still (somehow) prevent SIGINT from
interrupting the command.  I doubt if any implementation actually
does that.

The text should be reworded to refer only to inheritance.  I believe
it would be appropriate to require inheritance of a SIG_IGN signal
action, since that is the method used by most (or all?) current
shells.  However the new text should probably also allow SIGQUIT and
SIGINT to be blocked in the inherited signal mask, since the current
text allows implementations to do that.

A minor editorial correction should be made at the same time: the
paragraph refers to signal "values" which could be confused with the
numeric value (e.g. 2 for SIGINT) - it should use the proper term
("actions") instead.

Action:

Replace the first paragraph of section 2.11 with the following:

    "When a command is in an asynchronous list, it shall inherit
    from the shell a signal action of ignored (SIG_IGN) for the
    SIGQUIT and SIGINT signals and may inherit a signal mask in which
    SIGQUIT and SIGINT are blocked.  Otherwise, the signal actions
    and signal mask inherited by the command shall be the same as
    those inherited by the shell from its parent (see also the trap
    special built-in)."