On Tue, Aug 30, 2022 at 1:13 PM Shmulik Ladkani
<shmulik@xxxxxxxxxxxxxxxx> wrote:
>
> On Tue, 30 Aug 2022 23:02:57 +0300
> Shmulik Ladkani <shmulik@xxxxxxxxxxxxxxxx> wrote:
>
> > On Thu, 25 Aug 2022 11:20:31 -0700
> > Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
> >
> > > > + * long bpf_skb_set_tunnel_opt_dynptr(struct sk_buff *skb, struct bpf_dynptr *opt, u32 len)
> > >
> > > why can't we rely on dynptr's len instead of specifying extra one
> > > here? dynptr is a range of memory, so just specify that you take that
> > > entire range?
> > >
> > > And then we'll have (or partially already have) generic dynptr helpers
> > > to adjust internal dynptr offset and len.
> >
> > Alright.
> >
> > For my usecase I need to use *part* of the tunnel options that were
> > previously stored as a dynptr.
> >
> > Therefore I need to introduce a new bpf helper that adjusts the dynptr.
> >
> > How about this suggestion (sketch, not yet tried):
> >
> > // adjusts the dynptr to point to *len* bytes starting from the
> > // specified *offset*
> >
> > BPF_CALL_3(bpf_dynptr_slice, struct bpf_dynptr_kern *, ptr, u32, offset, u32, len)
> > {
> > int err;
> > u32 size;
> >
> > if (!ptr->data)
> > return -EINVAL;
> >
> > err = bpf_dynptr_check_off_len(ptr, offset, len);
> > if (err)
> > return err;
> >
> > ptr->offset += offset;
> > size = bpf_dynptr_get_size(ptr) - len;
> > ptr->size = (ptr->size & ~(u32)DYNPTR_SIZE_MASK) | size;
> > return 0;
> > }
> >
>
> Correction, meant:
> ptr->offset += offset;
> ptr->size = (ptr->size & ~(u32)DYNPTR_SIZE_MASK) | len;
>
I have a patchset for dynptr convenience helpers that I plan to tidy
up and push out later this week or mid-next week. it includes
"bpf_dynptr_advance()" and "bpf_dynptr_trim()", which will let you
adjust the dynptr ("_advance()" advances the offset, "_trim()" trims
the size)
