diff mbox series

[bpf-next,v6,06/13] xsk: Document tx_metadata_len layout

Message ID 20231127190319.1190813-7-sdf@google.com (mailing list archive)
State Accepted
Commit 9620e956d5b592d305728144931e89d780a598aa
Delegated to: BPF
Headers show
Series xsk: TX metadata | expand

Checks

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netdev/codegen success Generated files up to date
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 8 this patch: 8
netdev/cc_maintainers warning 4 maintainers not CCed: linux-doc@vger.kernel.org pabeni@redhat.com corbet@lwn.net edumazet@google.com
netdev/build_clang success Errors and warnings before: 8 this patch: 8
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 8 this patch: 8
netdev/checkpatch warning WARNING: Missing or malformed SPDX-License-Identifier tag in line 1 WARNING: added, moved or deleted file(s), does MAINTAINERS need updating?
netdev/build_clang_rust success No Rust files in patch. Skipping build
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bpf/vmtest-bpf-next-PR success PR summary

Commit Message

Stanislav Fomichev Nov. 27, 2023, 7:03 p.m. UTC 
- how to use
- how to query features
- pointers to the examples

Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 Documentation/networking/index.rst           |  1 +
 Documentation/networking/xdp-rx-metadata.rst |  2 +
 Documentation/networking/xsk-tx-metadata.rst | 70 ++++++++++++++++++++
 3 files changed, 73 insertions(+)
 create mode 100644 Documentation/networking/xsk-tx-metadata.rst

Comments

Simon Horman Dec. 2, 2023, 5:09 p.m. UTC | #1 
On Mon, Nov 27, 2023 at 11:03:12AM -0800, Stanislav Fomichev wrote:
> - how to use
> - how to query features
> - pointers to the examples
> 
> Signed-off-by: Stanislav Fomichev <sdf@google.com>

...

> diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
> index 205696780b78..e3e9420fd817 100644
> --- a/Documentation/networking/xdp-rx-metadata.rst
> +++ b/Documentation/networking/xdp-rx-metadata.rst
> @@ -1,3 +1,5 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
>  ===============
>  XDP RX Metadata
>  ===============
> diff --git a/Documentation/networking/xsk-tx-metadata.rst b/Documentation/networking/xsk-tx-metadata.rst
> new file mode 100644
> index 000000000000..4f376560b23f
> --- /dev/null
> +++ b/Documentation/networking/xsk-tx-metadata.rst

Hi Stan,

could you send a follow-up patch to add an SPDX identifier here?

> @@ -0,0 +1,70 @@
> +==================
> +AF_XDP TX Metadata
> +==================

...
Stanislav Fomichev Dec. 4, 2023, 4:48 p.m. UTC | #2 
On Sat, Dec 2, 2023 at 9:10 AM Simon Horman <horms@kernel.org> wrote:
>
> On Mon, Nov 27, 2023 at 11:03:12AM -0800, Stanislav Fomichev wrote:
> > - how to use
> > - how to query features
> > - pointers to the examples
> >
> > Signed-off-by: Stanislav Fomichev <sdf@google.com>
>
> ...
>
> > diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
> > index 205696780b78..e3e9420fd817 100644
> > --- a/Documentation/networking/xdp-rx-metadata.rst
> > +++ b/Documentation/networking/xdp-rx-metadata.rst
> > @@ -1,3 +1,5 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> >  ===============
> >  XDP RX Metadata
> >  ===============
> > diff --git a/Documentation/networking/xsk-tx-metadata.rst b/Documentation/networking/xsk-tx-metadata.rst
> > new file mode 100644
> > index 000000000000..4f376560b23f
> > --- /dev/null
> > +++ b/Documentation/networking/xsk-tx-metadata.rst
>
> Hi Stan,
>
> could you send a follow-up patch to add an SPDX identifier here?

Hmmm, I vividly remember adding it here after your initial comment :-/
Will send a follow up, thank you for catching it!
Simon Horman Dec. 7, 2023, 10:47 a.m. UTC | #3 
On Mon, Dec 04, 2023 at 08:48:46AM -0800, Stanislav Fomichev wrote:
> On Sat, Dec 2, 2023 at 9:10 AM Simon Horman <horms@kernel.org> wrote:
> >
> > On Mon, Nov 27, 2023 at 11:03:12AM -0800, Stanislav Fomichev wrote:
> > > - how to use
> > > - how to query features
> > > - pointers to the examples
> > >
> > > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> >
> > ...
> >
> > > diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
> > > index 205696780b78..e3e9420fd817 100644
> > > --- a/Documentation/networking/xdp-rx-metadata.rst
> > > +++ b/Documentation/networking/xdp-rx-metadata.rst
> > > @@ -1,3 +1,5 @@
> > > +.. SPDX-License-Identifier: GPL-2.0
> > > +
> > >  ===============
> > >  XDP RX Metadata
> > >  ===============
> > > diff --git a/Documentation/networking/xsk-tx-metadata.rst b/Documentation/networking/xsk-tx-metadata.rst
> > > new file mode 100644
> > > index 000000000000..4f376560b23f
> > > --- /dev/null
> > > +++ b/Documentation/networking/xsk-tx-metadata.rst
> >
> > Hi Stan,
> >
> > could you send a follow-up patch to add an SPDX identifier here?
> 
> Hmmm, I vividly remember adding it here after your initial comment :-/
> Will send a follow up, thank you for catching it!

Thanks, these things happen :)
diff mbox series

Patch

diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
index 683eb42309cc..a297a894b366 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -123,6 +123,7 @@  Refer to :ref:`netdev-FAQ` for a guide on netdev development process specifics.
    xfrm_sync
    xfrm_sysctl
    xdp-rx-metadata
+   xsk-tx-metadata
 
 .. only::  subproject and html
 
diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
index 205696780b78..e3e9420fd817 100644
--- a/Documentation/networking/xdp-rx-metadata.rst
+++ b/Documentation/networking/xdp-rx-metadata.rst
@@ -1,3 +1,5 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
 ===============
 XDP RX Metadata
 ===============
diff --git a/Documentation/networking/xsk-tx-metadata.rst b/Documentation/networking/xsk-tx-metadata.rst
new file mode 100644
index 000000000000..4f376560b23f
--- /dev/null
+++ b/Documentation/networking/xsk-tx-metadata.rst
@@ -0,0 +1,70 @@ 
+==================
+AF_XDP TX Metadata
+==================
+
+This document describes how to enable offloads when transmitting packets
+via :doc:`af_xdp`. Refer to :doc:`xdp-rx-metadata` on how to access similar
+metadata on the receive side.
+
+General Design
+==============
+
+The headroom for the metadata is reserved via ``tx_metadata_len`` in
+``struct xdp_umem_reg``. The metadata length is therefore the same for
+every socket that shares the same umem. The metadata layout is a fixed UAPI,
+refer to ``union xsk_tx_metadata`` in ``include/uapi/linux/if_xdp.h``.
+Thus, generally, the ``tx_metadata_len`` field above should contain
+``sizeof(union xsk_tx_metadata)``.
+
+The headroom and the metadata itself should be located right before
+``xdp_desc->addr`` in the umem frame. Within a frame, the metadata
+layout is as follows::
+
+           tx_metadata_len
+     /                         \
+    +-----------------+---------+----------------------------+
+    | xsk_tx_metadata | padding |          payload           |
+    +-----------------+---------+----------------------------+
+                                ^
+                                |
+                          xdp_desc->addr
+
+An AF_XDP application can request headrooms larger than ``sizeof(struct
+xsk_tx_metadata)``. The kernel will ignore the padding (and will still
+use ``xdp_desc->addr - tx_metadata_len`` to locate
+the ``xsk_tx_metadata``). For the frames that shouldn't carry
+any metadata (i.e., the ones that don't have ``XDP_TX_METADATA`` option),
+the metadata area is ignored by the kernel as well.
+
+The flags field enables the particular offload:
+
+- ``XDP_TXMD_FLAGS_TIMESTAMP``: requests the device to put transmission
+  timestamp into ``tx_timestamp`` field of ``union xsk_tx_metadata``.
+- ``XDP_TXMD_FLAGS_CHECKSUM``: requests the device to calculate L4
+  checksum. ``csum_start`` specifies byte offset of where the checksumming
+  should start and ``csum_offset`` specifies byte offset where the
+  device should store the computed checksum.
+
+Besides the flags above, in order to trigger the offloads, the first
+packet's ``struct xdp_desc`` descriptor should set ``XDP_TX_METADATA``
+bit in the ``options`` field. Also note that in a multi-buffer packet
+only the first chunk should carry the metadata.
+
+Querying Device Capabilities
+============================
+
+Every devices exports its offloads capabilities via netlink netdev family.
+Refer to ``xsk-flags`` features bitmask in
+``Documentation/netlink/specs/netdev.yaml``.
+
+- ``tx-timestamp``: device supports ``XDP_TXMD_FLAGS_TIMESTAMP``
+- ``tx-checksum``: device supports ``XDP_TXMD_FLAGS_CHECKSUM``
+
+See ``tools/net/ynl/samples/netdev.c`` on how to query this information.
+
+Example
+=======
+
+See ``tools/testing/selftests/bpf/xdp_hw_metadata.c`` for an example
+program that handles TX metadata. Also see https://github.com/fomichev/xskgen
+for a more bare-bones example.