Messages in this thread |  | | Date | Tue, 21 Aug 2018 16:35:49 -0700 | From | Doron Roberts-Kedes <> | Subject | Re: [PATCH] strparser: remove any offset before parsing messages |
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On Wed, Aug 22, 2018 at 12:51:13AM +0200, Dominique Martinet wrote: > That's maybe three more lines than the current patch, which is also > pretty simple, I'm not sure what you're expecting from alternative > solutions to call that overly complicated...
The line count is not the source of the complexity. The undue complexity is having strparser operate in two modes: one for clients that properly use the API by respecting the value of offset, and another for clients that do not.
> I don't think bpf itself needs to be changed here -- the offset is > stored in a strparser specific struct so short of such a skb_pull I > think we'd need to change the type of the bpf function, pass it it the > extra parameter, and make it a user visible change breaking the kcm > API... And I have no idea for sockmap but probably something similar.
I'm not sure I follow you here. Any rcv_msg callback implementation receives an skb. Calling strp_msg() on the skb gives you the strp_msg which has the offset value. Can you explain why passing an extra parameter is necessary to get the offset?
> I can't think of that as better than adding a flag to strparser. > > (Also, note that pskb_pull will not copy any data or allocate memory > unless we're pulling past the end of the skb, which seems pretty > unlikely in that situation as we should have consumed any fully "eaten" > skb before getting to a new one here -- so in practice this patch just > adds a skb->data += offset with safety guards "just in case")
Yes, no data will be copied if the you don't pull beyond the linear buffer. Adding overhead even in a small percentage of cases still requires a good justification. In this particular case, I think a good justification would be demonstrating that it is impractical for the buggy strparser users you've pointed out to use the existing API and respect the value of offset. You have indicated that you are not super familiar with the bpf code, which is fine (I'm not either), but this isn't a good reason to make a change to strparser instead of bpf.
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