netdev - Re: [PATCH net-next v9 14/15] p4tc: add set of P4TC table kfuncs

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Message-ID: <8faf1308-2f9f-4923-804e-8d9b11ba74e0@linux.dev>
Date: Thu, 7 Dec 2023 23:33:13 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jamal Hadi Salim <jhs@...atatu.com>
Cc: deb.chatterjee@...el.com, anjali.singhai@...el.com,
 namrata.limaye@...el.com, mleitner@...hat.com, Mahesh.Shirshyad@....com,
 tomasz.osinski@...el.com, jiri@...nulli.us, xiyou.wangcong@...il.com,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, vladbu@...dia.com, horms@...nel.org, khalidm@...dia.com,
 toke@...hat.com, daniel@...earbox.net, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH net-next v9 14/15] p4tc: add set of P4TC table kfuncs

On 12/1/23 10:29 AM, Jamal Hadi Salim wrote:
> We add an initial set of kfuncs to allow interactions from eBPF programs
> to the P4TC domain.
> 
> - bpf_p4tc_tbl_read: Used to lookup a table entry from a BPF
> program installed in TC. To find the table entry we take in an skb, the
> pipeline ID, the table ID, a key and a key size.
> We use the skb to get the network namespace structure where all the
> pipelines are stored. After that we use the pipeline ID and the table
> ID, to find the table. We then use the key to search for the entry.
> We return an entry on success and NULL on failure.
> 
> - xdp_p4tc_tbl_read: Used to lookup a table entry from a BPF
> program installed in XDP. To find the table entry we take in an xdp_md,
> the pipeline ID, the table ID, a key and a key size.
> We use struct xdp_md to get the network namespace structure where all
> the pipelines are stored. After that we use the pipeline ID and the table
> ID, to find the table. We then use the key to search for the entry.
> We return an entry on success and NULL on failure.
> 
> - bpf_p4tc_entry_create: Used to create a table entry from a BPF
> program installed in TC. To create the table entry we take an skb, the
> pipeline ID, the table ID, a key and its size, and an action which will
> be associated with the new entry.
> We return 0 on success and a negative errno on failure
> 
> - xdp_p4tc_entry_create: Used to create a table entry from a BPF
> program installed in XDP. To create the table entry we take an xdp_md, the
> pipeline ID, the table ID, a key and its size, and an action which will
> be associated with the new entry.
> We return 0 on success and a negative errno on failure
> 
> - bpf_p4tc_entry_create_on_miss: conforms to PNA "add on miss".
> First does a lookup using the passed key and upon a miss will add the entry
> to the table.
> We return 0 on success and a negative errno on failure
> 
> - xdp_p4tc_entry_create_on_miss: conforms to PNA "add on miss".
> First does a lookup using the passed key and upon a miss will add the entry
> to the table.
> We return 0 on success and a negative errno on failure
> 
> - bpf_p4tc_entry_update: Used to update a table entry from a BPF
> program installed in TC. To update the table entry we take an skb, the
> pipeline ID, the table ID, a key and its size, and an action which will
> be associated with the new entry.
> We return 0 on success and a negative errno on failure
> 
> - xdp_p4tc_entry_update: Used to update a table entry from a BPF
> program installed in XDP. To update the table entry we take an xdp_md, the
> pipeline ID, the table ID, a key and its size, and an action which will
> be associated with the new entry.
> We return 0 on success and a negative errno on failure
> 
> - bpf_p4tc_entry_delete: Used to delete a table entry from a BPF
> program installed in TC. To delete the table entry we take an skb, the
> pipeline ID, the table ID, a key and a key size.
> We return 0 on success and a negative errno on failure
> 
> - xdp_p4tc_entry_delete: Used to delete a table entry from a BPF
> program installed in XDP. To delete the table entry we take an xdp_md, the
> pipeline ID, the table ID, a key and a key size.
> We return 0 on success and a negative errno on failure

[ ... ]

> +BTF_SET8_START(p4tc_kfunc_check_tbl_set_skb)
> +BTF_ID_FLAGS(func, bpf_p4tc_tbl_read, KF_RET_NULL);
> +BTF_ID_FLAGS(func, bpf_p4tc_entry_create);
> +BTF_ID_FLAGS(func, bpf_p4tc_entry_create_on_miss);
> +BTF_ID_FLAGS(func, bpf_p4tc_entry_update);
> +BTF_ID_FLAGS(func, bpf_p4tc_entry_delete);
> +BTF_SET8_END(p4tc_kfunc_check_tbl_set_skb)

These create/read/update/delete kfuncs are like defining a new hidden bpf map 
type in the kernel. bpf prog can now create its own link-list and rbtree. 
sched_ext has already been using it. This is the way the bpf prog should use 
instead of creating a new map type.