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net: generalize calculation of skb extensions length 

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>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230823-skb_ext-simplify-v2-1-66e26cd66860@weissschuh.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Thomas Weißschuh 2023-08-23 11:28:38 +02:00 committed by Jakub Kicinski
parent 57ce6427e0
commit 5d21d0a65b
1 changed files with 7 additions and 17 deletions
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24
net/core/skbuff.c
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@ -4785,23 +4785,13 @@ static const u8 skb_ext_type_len[] = {
static __always_inline unsigned int skb_ext_total_length(void) static __always_inline unsigned int skb_ext_total_length(void)
{ {
return SKB_EXT_CHUNKSIZEOF(struct skb_ext) + unsigned int l = SKB_EXT_CHUNKSIZEOF(struct skb_ext);
#if IS_ENABLED(CONFIG_BRIDGE_NETFILTER) int i;
skb_ext_type_len[SKB_EXT_BRIDGE_NF] +
#endif for (i = 0; i < ARRAY_SIZE(skb_ext_type_len); i++)
#ifdef CONFIG_XFRM l += skb_ext_type_len[i];
skb_ext_type_len[SKB_EXT_SEC_PATH] +
#endif return l;
#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;
} }
static void skb_extensions_init(void) static void skb_extensions_init(void)