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commit 72bb3dbf0ecdf3ec96aee80e5d152c8be4394da1
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Author: Liping Zhang <zlpnobody@gmail.com>
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Date: Mon Feb 6 19:47:47 2017 +0800
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xshared: using the blocking file lock request when we wait indefinitely
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When using "-w" to avoid concurrent instances, we try to do flock() every
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one second until it success. But one second maybe too long in some
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situations, and it's hard to select a suitable interval time. So when
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using "iptables -w" to wait indefinitely, it's better to block until
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it become success.
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Now do some performance tests. First, flush all the iptables rules in
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filter table, and run "iptables -w -S" endlessly:
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# iptables -F
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# iptables -X
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# while : ; do
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iptables -w -S >&- &
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done
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Second, after adding and deleting the iptables rules 100 times, measure
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the time cost:
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# time for i in $(seq 100); do
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iptables -w -A INPUT
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iptables -w -D INPUT
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done
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Before this patch:
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real 1m15.962s
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user 0m0.224s
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sys 0m1.475s
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Apply this patch:
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real 0m1.830s
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user 0m0.168s
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sys 0m1.130s
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Signed-off-by: Liping Zhang <zlpnobody@gmail.com>
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Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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diff --git a/iptables/xshared.c b/iptables/xshared.c
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index 055acf2..f0a5ddd 100644
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--- a/iptables/xshared.c
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+++ b/iptables/xshared.c
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@@ -1,4 +1,5 @@
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#include <getopt.h>
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+#include <errno.h>
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#include <libgen.h>
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#include <netdb.h>
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#include <stdbool.h>
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@@ -258,27 +259,29 @@ bool xtables_lock(int wait, struct timeval *wait_interval)
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if (fd < 0)
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return true;
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+ if (wait == -1) {
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+ if (flock(fd, LOCK_EX) == 0)
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+ return true;
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+
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+ fprintf(stderr, "Can't lock %s: %s\n", XT_LOCK_NAME,
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+ strerror(errno));
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+ return false;
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+ }
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+
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while (1) {
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if (flock(fd, LOCK_EX | LOCK_NB) == 0)
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return true;
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- else if (wait >= 0 && timercmp(&time_left, wait_interval, <))
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+ else if (timercmp(&time_left, wait_interval, <))
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return false;
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if (++i % 10 == 0) {
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- if (wait != -1)
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- fprintf(stderr, "Another app is currently holding the xtables lock; "
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- "still %lds %ldus time ahead to have a chance to grab the lock...\n",
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- time_left.tv_sec, time_left.tv_usec);
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- else
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- fprintf(stderr, "Another app is currently holding the xtables lock; "
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- "waiting for it to exit...\n");
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+ fprintf(stderr, "Another app is currently holding the xtables lock; "
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+ "still %lds %ldus time ahead to have a chance to grab the lock...\n",
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+ time_left.tv_sec, time_left.tv_usec);
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}
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wait_time = *wait_interval;
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select(0, NULL, NULL, NULL, &wait_time);
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- if (wait == -1)
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- continue;
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-
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timersub(&time_left, wait_interval, &time_left);
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}
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}
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