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bpf: Add xdp dynptrs

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Add xdp dynptrs, which are dynptrs whose underlying pointer points
to a xdp_buff. The dynptr acts on xdp data. xdp dynptrs have two main
benefits. One is that they allow operations on sizes that are not
statically known at compile-time (eg variable-sized accesses).
Another is that parsing the packet data through dynptrs (instead of
through direct access of xdp->data and xdp->data_end) can be more
ergonomic and less brittle (eg does not need manual if checking for
being within bounds of data_end).

For reads and writes on the dynptr, this includes reading/writing
from/to and across fragments. Data slices through the bpf_dynptr_data
API are not supported; instead bpf_dynptr_slice() and
bpf_dynptr_slice_rdwr() should be used.

For examples of how xdp dynptrs can be used, please see the attached
selftests.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Link: https://lore.kernel.org/r/20230301154953.641654-9-joannelkoong@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Joanne Koong
2023-03-01 07:49:51 -08:00
committed by Alexei Starovoitov
parent b5964b968a
commit 05421aecd4
7 changed files with 76 additions and 6 deletions
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2
include/uapi/linux/bpf.h
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@@ -5344,7 +5344,7 @@ union bpf_attr {
* *len* must be a statically known value. The returned data slice
* is invalidated whenever the dynptr is invalidated.
*
* skb type dynptrs may not use bpf_dynptr_data. They should
* skb and xdp type dynptrs may not use bpf_dynptr_data. They should
* instead use bpf_dynptr_slice and bpf_dynptr_slice_rdwr.
* Return
* Pointer to the underlying dynptr data, NULL if the dynptr is