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Message-ID: <2878689.BEx9A2HvPv@sven-desktop>
Date: Sun, 28 Sep 2025 10:45:12 +0200
From: Sven Eckelmann <sven@...fation.org>
To: Eric Biggers <ebiggers@...nel.org>
Cc: Simon Wunderlich <sw@...onwunderlich.de>, kuba@...nel.org,
davem@...emloft.net, netdev@...r.kernel.org, b.a.t.m.a.n@...ts.open-mesh.org
Subject:
Re: [PATCH net-next 3/4] batman-adv: keep skb crc32 helper local in BLA
On Saturday, 27 September 2025 22:55:52 CEST Eric Biggers wrote:
> Hi,
>
> On Tue, Sep 16, 2025 at 02:24:40PM +0200, Simon Wunderlich wrote:
> > +static __be32 batadv_skb_crc32(struct sk_buff *skb, u8 *payload_ptr)
> > +{
> > + unsigned int to = skb->len;
> > + unsigned int consumed = 0;
> > + struct skb_seq_state st;
> > + unsigned int from;
> > + unsigned int len;
> > + const u8 *data;
> > + u32 crc = 0;
> > +
> > + from = (unsigned int)(payload_ptr - skb->data);
> > +
> > + skb_prepare_seq_read(skb, from, to, &st);
> > + while ((len = skb_seq_read(consumed, &data, &st)) != 0) {
> > + crc = crc32c(crc, data, len);
> > + consumed += len;
> > + }
> > +
> > + return htonl(crc);
> > +}
>
> Has using skb_crc32c() been considered here?
No. At the time this was written (v3.8), skb_crc32c (v6.16) didnt exist. Also
its predecessor __skb_checksum only started its existence in v3.13. And no one
noticed it as candidate to replace batadv_skb_crc32 with
And this patch here was just moving the function between two places - so not
introducing new code.
Do you want to submit a patch to integrate your new function in batman-adv? I
only performed a quick-and-dirty test to see if it returns the same results
and it seemed to do its job fine.
diff --git c/net/batman-adv/Kconfig w/net/batman-adv/Kconfig
index c299e2bc..58c408b7 100644
--- c/net/batman-adv/Kconfig
+++ w/net/batman-adv/Kconfig
@@ -35,6 +35,7 @@ config BATMAN_ADV_BLA
bool "Bridge Loop Avoidance"
depends on BATMAN_ADV && INET
select CRC16
+ select NET_CRC32C
default y
help
This option enables BLA (Bridge Loop Avoidance), a mechanism
diff --git c/net/batman-adv/bridge_loop_avoidance.c w/net/batman-adv/bridge_loop_avoidance.c
index b992ba12..eef40b6f 100644
--- c/net/batman-adv/bridge_loop_avoidance.c
+++ w/net/batman-adv/bridge_loop_avoidance.c
@@ -12,7 +12,6 @@
#include <linux/compiler.h>
#include <linux/container_of.h>
#include <linux/crc16.h>
-#include <linux/crc32.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/etherdevice.h>
@@ -1585,45 +1584,11 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
return 0;
}
-/**
- * batadv_skb_crc32() - calculate CRC32 of the whole packet and skip bytes in
- * the header
- * @skb: skb pointing to fragmented socket buffers
- * @payload_ptr: Pointer to position inside the head buffer of the skb
- * marking the start of the data to be CRC'ed
- *
- * payload_ptr must always point to an address in the skb head buffer and not to
- * a fragment.
- *
- * Return: big endian crc32c of the checksummed data
- */
-static __be32 batadv_skb_crc32(struct sk_buff *skb, u8 *payload_ptr)
-{
- unsigned int to = skb->len;
- unsigned int consumed = 0;
- struct skb_seq_state st;
- unsigned int from;
- unsigned int len;
- const u8 *data;
- u32 crc = 0;
-
- from = (unsigned int)(payload_ptr - skb->data);
-
- skb_prepare_seq_read(skb, from, to, &st);
- while ((len = skb_seq_read(consumed, &data, &st)) != 0) {
- crc = crc32c(crc, data, len);
- consumed += len;
- }
-
- return htonl(crc);
-}
-
/**
* batadv_bla_check_duplist() - Check if a frame is in the broadcast dup.
* @bat_priv: the bat priv with all the mesh interface information
* @skb: contains the multicast packet to be checked
- * @payload_ptr: pointer to position inside the head buffer of the skb
- * marking the start of the data to be CRC'ed
+ * @payload_offset: offset in the skb, marking the start of the data to be CRC'ed
* @orig: originator mac address, NULL if unknown
*
* Check if it is on our broadcast list. Another gateway might have sent the
@@ -1638,16 +1603,18 @@ static __be32 batadv_skb_crc32(struct sk_buff *skb, u8 *payload_ptr)
* Return: true if a packet is in the duplicate list, false otherwise.
*/
static bool batadv_bla_check_duplist(struct batadv_priv *bat_priv,
- struct sk_buff *skb, u8 *payload_ptr,
+ struct sk_buff *skb, int payload_offset,
const u8 *orig)
{
struct batadv_bcast_duplist_entry *entry;
bool ret = false;
+ int payload_len;
int i, curr;
__be32 crc;
/* calculate the crc ... */
- crc = batadv_skb_crc32(skb, payload_ptr);
+ payload_len = skb->len - payload_offset;
+ crc = htonl(skb_crc32c(skb, payload_offset, payload_len, 0));
spin_lock_bh(&bat_priv->bla.bcast_duplist_lock);
@@ -1727,7 +1694,7 @@ static bool batadv_bla_check_duplist(struct batadv_priv *bat_priv,
static bool batadv_bla_check_ucast_duplist(struct batadv_priv *bat_priv,
struct sk_buff *skb)
{
- return batadv_bla_check_duplist(bat_priv, skb, (u8 *)skb->data, NULL);
+ return batadv_bla_check_duplist(bat_priv, skb, 0, NULL);
}
/**
@@ -1745,12 +1712,10 @@ bool batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
struct sk_buff *skb)
{
struct batadv_bcast_packet *bcast_packet;
- u8 *payload_ptr;
bcast_packet = (struct batadv_bcast_packet *)skb->data;
- payload_ptr = (u8 *)(bcast_packet + 1);
- return batadv_bla_check_duplist(bat_priv, skb, payload_ptr,
+ return batadv_bla_check_duplist(bat_priv, skb, sizeof(*bcast_packet),
bcast_packet->orig);
}
Regards,
Sven
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