clj-ebpf.dsl.tc — org.clojars.pgdad/clj-ebpf 0.2.4

High-level TC (Traffic Control) DSL for BPF programs.

TC programs run on the traffic control layer and can be attached to qdisc (queueing discipline) ingress/egress points. They operate on sk_buff and provide access to more metadata than XDP.

TC Actions:

• TC_ACT_OK (0): Continue processing
• TC_ACT_SHOT (2): Drop packet
• TC_ACT_UNSPEC (-1): Use default action
• TC_ACT_PIPE (3): Continue to next action
• TC_ACT_RECLASSIFY (1): Restart classification
• TC_ACT_REDIRECT (7): Redirect packet

TC programs use __sk_buff as context, which provides richer packet metadata than XDP's xdp_md.

Example: (deftc-instructions simple-filter {:default-action :ok} ;; All packets passed [])

build-tc-program clj

(build-tc-program {:keys [ctx-reg data-reg data-end-reg body default-action]
                   :or {data-reg :r2 data-end-reg :r3 default-action :ok}})

Build a complete TC program with standard structure.

Parameters:

• opts: Map with: :ctx-reg - Register to save __sk_buff pointer (optional) :data-reg - Register for data pointer (default :r2) :data-end-reg - Register for data_end (default :r3) :body - Vector of body instructions :default-action - Default return action (default :ok)

Returns assembled program bytes.

deftc-instructions clj macro

(deftc-instructions fn-name options & body)

Define a TC program as a function returning instructions.

Parameters:

• fn-name: Name for the defined function
• options: Map with: :ctx-reg - Register to save context (optional) :data-reg - Register for data pointer (default :r2) :data-end-reg - Register for data_end (default :r3) :default-action - Default return action (default :ok)
• body: Body expressions (should return vectors of instructions)

Example: (deftc-instructions drop-all {:default-action :shot} [])

ethernet-header-size clj

ethernet-offsets clj

ethertypes clj

ip-protocols clj

ipv4-header-min-size clj

ipv4-offsets clj

ipv4-to-int clj

ipv6-header-size clj

ipv6-offsets clj

make-tc-program-info clj

(make-tc-program-info program-name instructions)

(make-tc-program-info program-name instructions direction)

(make-tc-program-info program-name instructions direction interface)

Create program metadata for a TC program.

Parameters:

• program-name: Name for the BPF program
• instructions: Program instructions
• direction: :ingress or :egress (optional)
• interface: Optional interface name

Returns map with program metadata.

skb-offset clj

(skb-offset field)

Get offset for __sk_buff field.

Parameters:

• field: Field keyword

Returns offset in bytes.

skb-offsets clj

__sk_buff structure field offsets.

tc-action clj

(tc-action action)

Get TC action value by keyword.

Parameters:

• action: Action keyword (:ok, :shot, :redirect, etc.)

Returns integer action value.

Example: (tc-action :shot) ;; => 2

tc-actions clj

TC action return values.

tc-bounds-check clj

Generate verifier-friendly bounds check for TC programs. Same as XDP bounds check since both use data/data_end pointers.

tc-classify-packet clj

(tc-classify-packet ctx-reg major minor)

Generate instructions to set TC classid.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• major: Major classid (upper 16 bits)
• minor: Minor classid (lower 16 bits)

Returns vector of instructions.

tc-clone-redirect clj

(tc-clone-redirect ctx-reg ifindex flags)

Generate call to bpf_clone_redirect helper.

Clones and redirects packet to another interface.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• ifindex: Interface index to redirect to
• flags: Redirect flags

Returns vector of instructions.

tc-get-hash clj

(tc-get-hash ctx-reg dst-reg)

Get packet hash from sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• dst-reg: Destination register

Returns ldx instruction.

tc-get-ifindex clj

(tc-get-ifindex ctx-reg dst-reg)

Get interface index from sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• dst-reg: Destination register

Returns ldx instruction.

tc-get-len clj

(tc-get-len ctx-reg dst-reg)

Get packet length from sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• dst-reg: Destination register

Returns ldx instruction.

tc-get-mark clj

(tc-get-mark ctx-reg dst-reg)

Get packet mark (fwmark) from sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• dst-reg: Destination register

Returns ldx instruction.

tc-get-priority clj

(tc-get-priority ctx-reg dst-reg)

Get packet priority from sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• dst-reg: Destination register

Returns ldx instruction.

tc-get-protocol clj

(tc-get-protocol ctx-reg dst-reg)

Get protocol (ETH_P_*) from sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• dst-reg: Destination register

Returns ldx instruction.

tc-get-tc-classid clj

(tc-get-tc-classid ctx-reg dst-reg)

Get TC classid from sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• dst-reg: Destination register

Returns ldx instruction.

tc-l3-csum-replace clj

(tc-l3-csum-replace ctx-reg offset from to flags)

Generate call to bpf_l3_csum_replace helper.

Updates L3 (IP) checksum.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• offset: Offset to checksum field
• from: Old value
• to: New value
• flags: Size flags

Returns vector of instructions.

tc-l4-csum-replace clj

(tc-l4-csum-replace ctx-reg offset from to flags)

Generate call to bpf_l4_csum_replace helper.

Updates L4 (TCP/UDP) checksum.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• offset: Offset to checksum field
• from: Old value
• to: New value
• flags: Size and pseudo-header flags

Returns vector of instructions.

tc-load-byte clj

tc-load-ctx-field clj

(tc-load-ctx-field ctx-reg field dst-reg)

Load a field from __sk_buff context.

Parameters:

• ctx-reg: Register containing __sk_buff pointer (typically :r1 at entry)
• field: Field keyword from skb-offsets
• dst-reg: Destination register

Returns ldx instruction.

tc-load-data-pointers clj

(tc-load-data-pointers ctx-reg data-reg data-end-reg)

Load data and data_end pointers from __sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• data-reg: Destination register for data pointer
• data-end-reg: Destination register for data_end pointer

Returns vector of instructions.

Example: (tc-load-data-pointers :r1 :r2 :r3) ;; r2 = data, r3 = data_end

tc-load-half clj

tc-load-word clj

tc-mark-packet clj

(tc-mark-packet ctx-reg mark)

Generate instructions to set packet mark.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• mark: Mark value to set

Returns vector of instructions.

tc-match-mark clj

(tc-match-mark ctx-reg mark action-on-match)

Generate instructions to match packet mark.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• mark: Mark value to match
• action-on-match: TC action if mark matches

Returns vector of instructions.

tc-parse-ethernet clj

tc-parse-ipv4 clj

tc-parse-ipv6 clj

tc-parse-tcp clj

tc-parse-udp clj

tc-prologue clj

(tc-prologue data-reg data-end-reg)

(tc-prologue ctx-save-reg data-reg data-end-reg)

Generate standard TC program prologue.

Saves context and loads data pointers.

Parameters:

• ctx-save-reg: Register to save __sk_buff pointer (optional)
• data-reg: Register for data pointer
• data-end-reg: Register for data_end pointer

Returns vector of instructions.

tc-redirect clj

(tc-redirect ifindex flags)

Generate call to bpf_redirect helper.

Redirects packet to another interface.

Parameters:

• ifindex: Interface index to redirect to
• flags: Redirect flags (usually 0)

Returns vector of instructions.

tc-return-action clj

(tc-return-action action)

Generate instructions to return a TC action.

Parameters:

• action: Action keyword or integer

Returns vector of [mov, exit] instructions.

tc-section-name clj

(tc-section-name)

(tc-section-name direction)

(tc-section-name direction interface)

Generate ELF section name for TC program.

Parameters:

• direction: :ingress or :egress
• interface: Optional interface name

Returns section name like "tc" or "tc/ingress/eth0"

tc-set-mark clj

(tc-set-mark ctx-reg value-reg)

Set packet mark (fwmark) in sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• value-reg: Register containing mark value

Returns stx instruction.

tc-set-priority clj

(tc-set-priority ctx-reg value-reg)

Set packet priority in sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• value-reg: Register containing priority value

Returns stx instruction.

tc-set-tc-classid clj

(tc-set-tc-classid ctx-reg value-reg)

Set TC classid in sk_buff.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• value-reg: Register containing classid value

Returns stx instruction.

tc-skb-change-head clj

(tc-skb-change-head ctx-reg len-diff flags)

Generate call to bpf_skb_change_head helper.

Adjusts packet headroom.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• len-diff: Bytes to add (positive) or remove (negative)
• flags: Flags (usually 0)

Returns vector of instructions.

tc-skb-change-tail clj

(tc-skb-change-tail ctx-reg new-len flags)

Generate call to bpf_skb_change_tail helper.

Adjusts packet tail.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• new-len: New packet length
• flags: Flags (usually 0)

Returns vector of instructions.

tc-skb-load-bytes clj

(tc-skb-load-bytes ctx-reg offset dst-reg len)

Generate call to bpf_skb_load_bytes helper.

Loads bytes from packet data.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• offset: Offset into packet
• dst-reg: Register with pointer to destination buffer
• len: Length to load

Returns vector of instructions.

tc-skb-store-bytes clj

(tc-skb-store-bytes ctx-reg offset data-reg len flags)

Generate call to bpf_skb_store_bytes helper.

Stores bytes into packet data.

Parameters:

• ctx-reg: Register containing __sk_buff pointer
• offset: Offset into packet
• data-reg: Register with pointer to data
• len: Length to store
• flags: Flags (usually 0)

Returns vector of instructions.

tcp-flags clj

tcp-header-min-size clj

tcp-offsets clj

udp-header-size clj

udp-offsets clj