iptables: add -C to check for existing rules

It is often useful to check whether a specific rule is already present
in a chain without actually modifying the iptables config.

Services like fail2ban usually employ techniques like grepping through
the output of "iptables -L" which is quite error prone.

This patch adds a new operation -C to the iptables command which
mostly works like -D; it can detect and indicate the existence of the
specified rule by modifying the exit code. The new operation
TC_CHECK_ENTRY uses the same code as the -D operation, whose functions
got a dry-run parameter appended.

Signed-off-by: Stefan Tomanek <stefan.tomanek@wertarbyte.de>
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>

0 files changed, 0 insertions, 0 deletions