Messages in this thread Patch in this message | | | From | Thomas Weißschuh <> | Date | Wed, 23 Aug 2023 11:28:38 +0200 | Subject | [PATCH net-next v2] net: generalize calculation of skb extensions length |
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Remove the necessity to modify skb_ext_total_length() when new extension types are added. Also reduces the line count a bit.
With optimizations enabled the function is folded down to the same constant value as before during compilation. This has been validated on x86 with GCC 6.5.0 and 13.2.1. Also a similar construct has been validated on godbolt.org with GCC 5.1. In any case the compiler has to be able to evaluate the construct at compile-time for the BUILD_BUG_ON() in skb_extensions_init().
Even if not evaluated at compile-time this function would only ever be executed once at run-time, so the overhead would be very minuscule.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net> --- Changes in v2: - Add more proof for identical behavior to the commit log - Link to v1: https://lore.kernel.org/r/20230822-skb_ext-simplify-v1-1-9dd047340ab5@weissschuh.net --- net/core/skbuff.c | 24 +++++++----------------- 1 file changed, 7 insertions(+), 17 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index faa6c86da2a5..45707059082f 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4785,23 +4785,13 @@ static const u8 skb_ext_type_len[] = { static __always_inline unsigned int skb_ext_total_length(void) { - return SKB_EXT_CHUNKSIZEOF(struct skb_ext) + -#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER) - skb_ext_type_len[SKB_EXT_BRIDGE_NF] + -#endif -#ifdef CONFIG_XFRM - skb_ext_type_len[SKB_EXT_SEC_PATH] + -#endif -#if IS_ENABLED(CONFIG_NET_TC_SKB_EXT) - skb_ext_type_len[TC_SKB_EXT] + -#endif -#if IS_ENABLED(CONFIG_MPTCP) - skb_ext_type_len[SKB_EXT_MPTCP] + -#endif -#if IS_ENABLED(CONFIG_MCTP_FLOWS) - skb_ext_type_len[SKB_EXT_MCTP] + -#endif - 0; + unsigned int l = SKB_EXT_CHUNKSIZEOF(struct skb_ext); + int i; + + for (i = 0; i < ARRAY_SIZE(skb_ext_type_len); i++) + l += skb_ext_type_len[i]; + + return l; } static void skb_extensions_init(void) --- base-commit: 90308679c297ffcbb317c715ef434e9fb3c881dc change-id: 20230822-skb_ext-simplify-3d93ceb95f62 Best regards, -- Thomas Weißschuh <linux@weissschuh.net>
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