ddb: enable the use of ^C and ^S/^Q

This lets one interrupt DDB's output, which is useful if paging is
disabled and the output device is slow.

This follows a previous implementation in svn r311952 / git
5fddef79998678d256ba30316353393b4d8ebb32 which was reverted because it
broke DDB type-ahead.

Now, try this again, but with a 512-byte type-ahead buffer.  While there
is buffer space, control input is handled and non-control input is
buffered.  When the buffer is exhausted, the default is to print a
warning and drop further non-control input in order to continue handling
control input.  sysctl debug.ddb.prioritize_control_input can be set to
0 to instead preserve all input but lose immediate handling of control
input.  This could for example effect pasting of a large script into the
ddb console.

Suggested by:	Anton Rang <rang@acm.org>
Reviewed by:	markj
Discussed with:	imp
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D28676

0 files changed, 0 insertions, 0 deletions