On 6/2/20 6:41 PM, Alan Maguire wrote:
On Tue, 2 Jun 2020, Daniel Borkmann wrote:
On 6/2/20 5:19 PM, Lorenz Bauer wrote:
On Tue, 2 Jun 2020 at 15:58, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
Add a bpf_csum_level() helper which BPF programs can use in combination
with bpf_skb_adjust_room() when they pass in BPF_F_ADJ_ROOM_NO_CSUM_RESET
flag to the latter to avoid falling back to CHECKSUM_NONE.
The bpf_csum_level() allows to adjust CHECKSUM_UNNECESSARY skb->csum_levels
via BPF_CSUM_LEVEL_{INC,DEC} which calls
__skb_{incr,decr}_checksum_unnecessary()
on the skb. The helper also allows a BPF_CSUM_LEVEL_RESET which sets the
skb's
csum to CHECKSUM_NONE as well as a BPF_CSUM_LEVEL_QUERY to just return the
current level. Without this helper, there is no way to otherwise adjust the
skb->csum_level. I did not add an extra dummy flags as there is plenty of
free
bitspace in level argument itself iff ever needed in future.
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
---
include/uapi/linux/bpf.h | 43 +++++++++++++++++++++++++++++++++-
net/core/filter.c | 38 ++++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 43 +++++++++++++++++++++++++++++++++-
3 files changed, 122 insertions(+), 2 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 3ba2bbbed80c..46622901cba7 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3220,6 +3220,38 @@ union bpf_attr {
* calculation.
* Return
* Requested value, or 0, if flags are not recognized.
+ *
+ * int bpf_csum_level(struct sk_buff *skb, u64 level)
u64 flags? We can also stuff things into level I guess.
Yeah, I did mention it in the commit log. There is plenty of bit space to
extend
with flags in there iff ever needed. Originally, helper was called
bpf_csum_adjust()
but then renamed into bpf_csum_level() to be more 'topic specific' (aka do one
thing
and do it well...) and avoid future api overloading, so if necessary level can
be
used since I don't think the enum will be extended much further from what we
have
here anyway.
[...]
Acked-by: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>
Looks great! The only thing that gave me pause was
the -EACCES return value for the case where we query
and the skb is not subject to CHECKSUM_UNNECESSESARY ;
-ENOENT ("no such level") feels slightly closer to the
situation to me but either is a reasonable choice I think.
My thinking was in the line of 'error since we cannot access skb->csum_level
for the given skb->ip_summed'. I don't feel strong about which code it is either
way though; important thing is that it is documented & distinguishable from
other errors, so that the program has a way to make sense of the data returned
by BPF_CSUM_LEVEL_QUERY.
Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
Thanks!
Daniel
