xtables-restore: Improve performance of --noflush operation

The reason for that full cache fetching when called with --noflush even
before looking at any input data was that there might be a command
requiring a rule cache following some rule add/insert ones which don't.
At that point one needs to fetch rules from kernel and try to insert the
local ones at the right spot which is non-trivial.

At the same time there is a performance-critical use-case for --noflush,
namely fast insertion of a bunch of rules in one go, avoiding the
process spawn overhead.

Optimize for this use-case by preloading input into a 64KB buffer to see
if it fits. If so, search for commands requiring a rule cache. If there
are none, skip initial full cache fetching.

The above algorithm may abort at any point, so actual input parsing must
happen in three stages:

1) parse all preloaded lines from 64KB buffer
2) parse any leftover line in line buffer (happens if input exceeds
   the preload buffer size)
3) parse remaining input from input file pointer

Signed-off-by: Phil Sutter <phil@nwl.cc>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

0 files changed, 0 insertions, 0 deletions