netdev - [PATCH bpf-next 2/3] net: skbuff: reorder bytes 2 and 3 of the bitfield

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Date:   Tue,  7 Mar 2023 16:31:58 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     bpf@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
        pabeni@...hat.com, Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH bpf-next 2/3] net: skbuff: reorder bytes 2 and 3 of the bitfield

BPF needs to know the offsets of fields it tries to access.
Zero-length fields are added to make offsetof() work.
This unfortunately partitions the bitfield (fields across
the zero-length members can't be coalesced).

Reorder bytes 2 and 3, BPF needs to know the offset of fields
previously in byte 3 and some fields in byte 2 should really
be optional.

The two bytes are always in the same cacheline so it should
not matter.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
 include/linux/skbuff.h | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 004009b3930f..c4122797d465 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -945,16 +945,6 @@ struct sk_buff {
 	__u8			ip_summed:2;
 	__u8			ooo_okay:1;
 
-	__u8			l4_hash:1;
-	__u8			sw_hash:1;
-	__u8			wifi_acked_valid:1;
-	__u8			wifi_acked:1;
-	__u8			no_fcs:1;
-	/* Indicates the inner headers are valid in the skbuff. */
-	__u8			encapsulation:1;
-	__u8			encap_hdr_csum:1;
-	__u8			csum_valid:1;
-
 	/* private: */
 	__u8			__mono_tc_offset[0];
 	/* public: */
@@ -967,6 +957,16 @@ struct sk_buff {
 	__u8			tc_skip_classify:1;
 	__u8			tc_at_ingress:1;	/* See TC_AT_INGRESS_MASK */
 #endif
+
+	__u8			l4_hash:1;
+	__u8			sw_hash:1;
+	__u8			wifi_acked_valid:1;
+	__u8			wifi_acked:1;
+	__u8			no_fcs:1;
+	/* Indicates the inner headers are valid in the skbuff. */
+	__u8			encapsulation:1;
+	__u8			encap_hdr_csum:1;
+	__u8			csum_valid:1;
 #ifdef CONFIG_IPV6_NDISC_NODETYPE
 	__u8			ndisc_nodetype:2;
 #endif
-- 
2.39.2