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-rw-r--r--Documentation/networking/filter.txt13
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index 81f940f4e884..82e1cb0b3da8 100644
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -281,6 +281,7 @@ Possible BPF extensions are shown in the following table:
cpu raw_smp_processor_id()
vlan_tci vlan_tx_tag_get(skb)
vlan_pr vlan_tx_tag_present(skb)
+ rand prandom_u32()
These extensions can also be prefixed with '#'.
Examples for low-level BPF:
@@ -308,6 +309,18 @@ Examples for low-level BPF:
ret #-1
drop: ret #0
+** icmp random packet sampling, 1 in 4
+ ldh [12]
+ jne #0x800, drop
+ ldb [23]
+ jneq #1, drop
+ # get a random uint32 number
+ ld rand
+ mod #4
+ jneq #1, drop
+ ret #-1
+ drop: ret #0
+
** SECCOMP filter example:
ld [4] /* offsetof(struct seccomp_data, arch) */