Subject: [PATCH] netfilter: factorize ifname_compare()

From: Eric Dumazet <[email-masked]>
Date: Wed, 25 Mar 2009 12:27:07 +0100

Jan Engelhardt a écrit :
> On Tuesday 2009-03-24 22:39, Eric Dumazet wrote:
>> memcmp() is fine, but how is it solving the masking problem we have ?
> 
> You are right; we would have to calculate the prefix length of the
> mask first. (And I think we can assume that there will not be any 1s
> in the mask after the first 0.) It would consume CPU indeed.
> 
>> Also in the case of arp_tables, _a is long word aligned, while _b and _mask
>> are not.
>>
>> If you look various ifname_compare(), we have two different implementations.
>>
>> So yes, a factorization is possible for three ip_tables.c, ip6_tables.c and
>> xt_physdev.c.
> 
> Very well.

Here is a patch to factorize these functions, as suggested by Jan

Thank you

[PATCH] netfilter: factorize ifname_compare()

We use same not trivial helper function in four places. We can factorize it.

Signed-off-by: Eric Dumazet <[email-masked]>
---
 include/linux/netfilter/x_tables.h |   23 +++++++++++++++++++++++
 net/ipv4/netfilter/arp_tables.c    |   14 +-------------
 net/ipv4/netfilter/ip_tables.c     |   23 ++---------------------
 net/ipv6/netfilter/ip6_tables.c    |   23 ++---------------------
 net/netfilter/xt_physdev.c         |   21 ++-------------------
 5 files changed, 30 insertions(+), 74 deletions(-)

diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index e8e08d0..72918b7 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -435,6 +435,29 @@ extern void xt_free_table_info(struct xt_table_info *info);
 extern void xt_table_entry_swap_rcu(struct xt_table_info *old,
 				    struct xt_table_info *new);
 
+/*
+ * This helper is performance critical and must be inlined
+ */
+static inline unsigned long ifname_compare_aligned(const char *_a,
+						   const char *_b,
+						   const char *_mask)
+{
+	const unsigned long *a = (const unsigned long *)_a;
+	const unsigned long *b = (const unsigned long *)_b;
+	const unsigned long *mask = (const unsigned long *)_mask;
+	unsigned long ret;
+
+	ret = (a[0] ^ b[0]) & mask[0];
+	if (IFNAMSIZ > sizeof(unsigned long))
+		ret |= (a[1] ^ b[1]) & mask[1];
+	if (IFNAMSIZ > 2 * sizeof(unsigned long))
+		ret |= (a[2] ^ b[2]) & mask[2];
+	if (IFNAMSIZ > 3 * sizeof(unsigned long))
+		ret |= (a[3] ^ b[3]) & mask[3];
+	BUILD_BUG_ON(IFNAMSIZ > 4 * sizeof(unsigned long));
+	return ret;
+}
+
 #ifdef CONFIG_COMPAT
 #include <net/compat.h>
 
diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
index 84b9c17..ee1133c 100644
--- a/net/ipv4/netfilter/arp_tables.c
+++ b/net/ipv4/netfilter/arp_tables.c
@@ -81,19 +81,7 @@ static inline int arp_devaddr_compare(const struct arpt_devaddr_info *ap,
 static unsigned long ifname_compare(const char *_a, const char *_b, const char *_mask)
 {
 #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
-	const unsigned long *a = (const unsigned long *)_a;
-	const unsigned long *b = (const unsigned long *)_b;
-	const unsigned long *mask = (const unsigned long *)_mask;
-	unsigned long ret;
-
-	ret = (a[0] ^ b[0]) & mask[0];
-	if (IFNAMSIZ > sizeof(unsigned long))
-		ret |= (a[1] ^ b[1]) & mask[1];
-	if (IFNAMSIZ > 2 * sizeof(unsigned long))
-		ret |= (a[2] ^ b[2]) & mask[2];
-	if (IFNAMSIZ > 3 * sizeof(unsigned long))
-		ret |= (a[3] ^ b[3]) & mask[3];
-	BUILD_BUG_ON(IFNAMSIZ > 4 * sizeof(unsigned long));
+	unsigned long ret = ifname_compare_aligned(_a, _b, _mask);
 #else
 	unsigned long ret = 0;
 	const u16 *a = (const u16 *)_a;
diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
index e5294ae..41c59e3 100644
--- a/net/ipv4/netfilter/ip_tables.c
+++ b/net/ipv4/netfilter/ip_tables.c
@@ -74,25 +74,6 @@ do {								\
 
    Hence the start of any table is given by get_table() below.  */
 
-static unsigned long ifname_compare(const char *_a, const char *_b,
-				    const unsigned char *_mask)
-{
-	const unsigned long *a = (const unsigned long *)_a;
-	const unsigned long *b = (const unsigned long *)_b;
-	const unsigned long *mask = (const unsigned long *)_mask;
-	unsigned long ret;
-
-	ret = (a[0] ^ b[0]) & mask[0];
-	if (IFNAMSIZ > sizeof(unsigned long))
-		ret |= (a[1] ^ b[1]) & mask[1];
-	if (IFNAMSIZ > 2 * sizeof(unsigned long))
-		ret |= (a[2] ^ b[2]) & mask[2];
-	if (IFNAMSIZ > 3 * sizeof(unsigned long))
-		ret |= (a[3] ^ b[3]) & mask[3];
-	BUILD_BUG_ON(IFNAMSIZ > 4 * sizeof(unsigned long));
-	return ret;
-}
-
 /* Returns whether matches rule or not. */
 /* Performance critical - called for every packet */
 static inline bool
@@ -121,7 +102,7 @@ ip_packet_match(const struct iphdr *ip,
 		return false;
 	}
 
-	ret = ifname_compare(indev, ipinfo->iniface, ipinfo->iniface_mask);
+	ret = ifname_compare_aligned(indev, ipinfo->iniface, ipinfo->iniface_mask);
 
 	if (FWINV(ret != 0, IPT_INV_VIA_IN)) {
 		dprintf("VIA in mismatch (%s vs %s).%s\n",
@@ -130,7 +111,7 @@ ip_packet_match(const struct iphdr *ip,
 		return false;
 	}
 
-	ret = ifname_compare(outdev, ipinfo->outiface, ipinfo->outiface_mask);
+	ret = ifname_compare_aligned(outdev, ipinfo->outiface, ipinfo->outiface_mask);
 
 	if (FWINV(ret != 0, IPT_INV_VIA_OUT)) {
 		dprintf("VIA out mismatch (%s vs %s).%s\n",
diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
index 34af7bb..e59662b 100644
--- a/net/ipv6/netfilter/ip6_tables.c
+++ b/net/ipv6/netfilter/ip6_tables.c
@@ -89,25 +89,6 @@ ip6t_ext_hdr(u8 nexthdr)
 		 (nexthdr == IPPROTO_DSTOPTS) );
 }
 
-static unsigned long ifname_compare(const char *_a, const char *_b,
-				    const unsigned char *_mask)
-{
-	const unsigned long *a = (const unsigned long *)_a;
-	const unsigned long *b = (const unsigned long *)_b;
-	const unsigned long *mask = (const unsigned long *)_mask;
-	unsigned long ret;
-
-	ret = (a[0] ^ b[0]) & mask[0];
-	if (IFNAMSIZ > sizeof(unsigned long))
-		ret |= (a[1] ^ b[1]) & mask[1];
-	if (IFNAMSIZ > 2 * sizeof(unsigned long))
-		ret |= (a[2] ^ b[2]) & mask[2];
-	if (IFNAMSIZ > 3 * sizeof(unsigned long))
-		ret |= (a[3] ^ b[3]) & mask[3];
-	BUILD_BUG_ON(IFNAMSIZ > 4 * sizeof(unsigned long));
-	return ret;
-}
-
 /* Returns whether matches rule or not. */
 /* Performance critical - called for every packet */
 static inline bool
@@ -138,7 +119,7 @@ ip6_packet_match(const struct sk_buff *skb,
 		return false;
 	}
 
-	ret = ifname_compare(indev, ip6info->iniface, ip6info->iniface_mask);
+	ret = ifname_compare_aligned(indev, ip6info->iniface, ip6info->iniface_mask);
 
 	if (FWINV(ret != 0, IP6T_INV_VIA_IN)) {
 		dprintf("VIA in mismatch (%s vs %s).%s\n",
@@ -147,7 +128,7 @@ ip6_packet_match(const struct sk_buff *skb,
 		return false;
 	}
 
-	ret = ifname_compare(outdev, ip6info->outiface, ip6info->outiface_mask);
+	ret = ifname_compare_aligned(outdev, ip6info->outiface, ip6info->outiface_mask);
 
 	if (FWINV(ret != 0, IP6T_INV_VIA_OUT)) {
 		dprintf("VIA out mismatch (%s vs %s).%s\n",
diff --git a/net/netfilter/xt_physdev.c b/net/netfilter/xt_physdev.c
index 44a234e..8d28ca5 100644
--- a/net/netfilter/xt_physdev.c
+++ b/net/netfilter/xt_physdev.c
@@ -20,23 +20,6 @@ MODULE_DESCRIPTION("Xtables: Bridge physical device match");
 MODULE_ALIAS("ipt_physdev");
 MODULE_ALIAS("ip6t_physdev");
 
-static unsigned long ifname_compare(const char *_a, const char *_b, const char *_mask)
-{
-	const unsigned long *a = (const unsigned long *)_a;
-	const unsigned long *b = (const unsigned long *)_b;
-	const unsigned long *mask = (const unsigned long *)_mask;
-	unsigned long ret;
-
-	ret = (a[0] ^ b[0]) & mask[0];
-	if (IFNAMSIZ > sizeof(unsigned long))
-		ret |= (a[1] ^ b[1]) & mask[1];
-	if (IFNAMSIZ > 2 * sizeof(unsigned long))
-		ret |= (a[2] ^ b[2]) & mask[2];
-	if (IFNAMSIZ > 3 * sizeof(unsigned long))
-		ret |= (a[3] ^ b[3]) & mask[3];
-	BUILD_BUG_ON(IFNAMSIZ > 4 * sizeof(unsigned long));
-	return ret;
-}
 
 static bool
 physdev_mt(const struct sk_buff *skb, const struct xt_match_param *par)
@@ -85,7 +68,7 @@ physdev_mt(const struct sk_buff *skb, const struct xt_match_param *par)
 	if (!(info->bitmask & XT_PHYSDEV_OP_IN))
 		goto match_outdev;
 	indev = nf_bridge->physindev ? nf_bridge->physindev->name : nulldevname;
-	ret = ifname_compare(indev, info->physindev, info->in_mask);
+	ret = ifname_compare_aligned(indev, info->physindev, info->in_mask);
 
 	if (!ret ^ !(info->invert & XT_PHYSDEV_OP_IN))
 		return false;
@@ -95,7 +78,7 @@ match_outdev:
 		return true;
 	outdev = nf_bridge->physoutdev ?
 		 nf_bridge->physoutdev->name : nulldevname;
-	ret = ifname_compare(outdev, info->physoutdev, info->out_mask);
+	ret = ifname_compare_aligned(outdev, info->physoutdev, info->out_mask);
 
 	return (!!ret ^ !(info->invert & XT_PHYSDEV_OP_OUT));
 }