Thread (22 messages) 22 messages, 3 authors, 2024-09-09

Re: [PATCH net-next v24 11/13] net: add devmem TCP documentation

From: Jakub Kicinski <kuba@kernel.org>
Date: 2024-09-03 21:51:53
Also in: bpf, dri-devel, linux-alpha, linux-arch, linux-doc, linux-kselftest, linux-media, linux-mips, linux-trace-kernel, lkml, sparclinux

On Sat, 31 Aug 2024 00:43:11 +0000 Mina Almasry wrote:
+The socket must be flow steered to the dmabuf bound RX queue::
+
+	ethtool -N eth1 flow-type tcp4 ... queue 15,
nit: tailing comma here
+Devmem payloads are inaccessible to the kernel processing the packets. This
+results in a few quirks for payloads of devmem skbs:
+
+- Loopback is not functional. Loopback relies on copying the payload, which is
+  not possible with devmem skbs.
+
+- Software checksum calculation fails.
Speaking of which, I think we need to add readability check to 
skb_checksum_help(). Shouldn't the check in __skb_checksum() 
have a WARN_ON_ONCE() around it? It's impossible to return 
an error from there.
+- TCP Dump and bpf can't access devmem packet payloads.
+
+
+Testing
+=======
+
+More realistic example code can be found in the kernel source under
+tools/testing/selftests/net/ncdevmem.c
looks like HTML output wraps the file path, maybe quote it as
``tools/testing/selftests/net/ncdevmem.c`` ?
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