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bpf: Clarify role of BPF_F_RECOMPUTE_CSUM

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BPF_F_RECOMPUTE_CSUM doesn't update the actual L3 and L4 checksums in
the packet, but simply updates skb->csum (according to skb->ip_summed).
This patch clarifies that to avoid confusions.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Link: https://lore.kernel.org/r/ff6895d42936f03dbb82334d8bcfd50e00c79086.1744102490.git.paul.chaignon@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Paul Chaignon
2025-04-08 11:00:04 +02:00
committed by Andrii Nakryiko
parent abdb15bedd
commit 7de6a44a0f
1 changed files with 9 additions and 5 deletions
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14
include/uapi/linux/bpf.h
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@@ -1995,11 +1995,15 @@ union bpf_attr {
* long bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from, u32 len, u64 flags)
* Description
* Store *len* bytes from address *from* into the packet
* associated to *skb*, at *offset*. *flags* are a combination of
* **BPF_F_RECOMPUTE_CSUM** (automatically recompute the
* checksum for the packet after storing the bytes) and
* **BPF_F_INVALIDATE_HASH** (set *skb*\ **->hash**, *skb*\
* **->swhash** and *skb*\ **->l4hash** to 0).
* associated to *skb*, at *offset*. The *flags* are a combination
* of the following values:
*
* **BPF_F_RECOMPUTE_CSUM**
* Automatically update *skb*\ **->csum** after storing the
* bytes.
* **BPF_F_INVALIDATE_HASH**
* Set *skb*\ **->hash**, *skb*\ **->swhash** and *skb*\
* **->l4hash** to 0.
*
* A call to this helper is susceptible to change the underlying
* packet buffer. Therefore, at load time, all checks on pointers