STRUCT ETHTOOL_TEST(9)

🌸 NAME 🌸

struct ethtool_test — device self-test invocation 💅 (yes, the actual "hey bestie, run a self-test on this NIC" struct)

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✨ SYNOPSIS ✨

struct ethtool_test {
    __u32 cmd;
    __u32 flags;
    __u32 reserved;
    __u32 len;
    __u64 data[];
 };

Okay so this is the struct, it's giving very "header + flexible array member" realness, and here's what each little field is doing 👇

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💅 MEMBERS 💅

🌟 cmd

Command number = ETHTOOL_TEST. That's the whole vibe — this is the magic number that tells the kernel "hi, we're doing the self-test thing today."

🎀 flags

A bitmask of flags from enum ethtool_test_flags. Some flags may be set by the user on entry; others may be set by the driver on return. So it's a two-way conversation, not a monologue — lowkey iconic 🫶

🦋 reserved

Reserved for future use; see the note on reserved space. Bestie, do not touch this. It's saving its seat for future main character energy 👑

🔥 len

On return, the number of test results. So you don't know it going in — the kernel tells you on the way out. Surprise reveal, we love that for you ✨

💜 data

Array of test results. The payload! The moment! The whole point!

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🌈 DESCRIPTION 🌈

Okay so here's the tea ☕ — users must use ETHTOOL_GSSET_INFO or ETHTOOL_GDRVINFO to find the number of test results that will be returned.

Then (and this is the part people always mess up, ngl) they must allocate a buffer of the appropriate size (8 * number of results) immediately following this structure. Immediately. Right after it. Not on a different allocation, not off in a corner — it lives right up against this struct, no cap 🫶

So the mental picture is: this struct, and then 8 * number of results bytes of results trailing behind it like a little squad ✨

Not me emphasizing "immediately following this structure" twice — it's because that's literally the whole design, bestie. Respect the layout 💀

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🎀 SEE ALSO 🎀

Kernel file ./include/uapi/linux/ethtool.h — and a whole friend group of structs/enums:

• struct ethtool_cmd(9)
• struct ethtool_drvinfo(9)
• struct ethtool_wolinfo(9)
• struct ethtool_regs(9)
• struct ethtool_eeprom(9)
• struct ethtool_eee(9)
• struct ethtool_modinfo(9)
• struct ethtool_coalesce(9)
• struct ethtool_ringparam(9)
• struct ethtool_channels(9)
• struct ethtool_pauseparam(9)
• enum ethtool_stringset(9)
• enum ethtool_mac_stats_src(9)
• enum ethtool_module_power_mode_policy(9)
• enum ethtool_module_power_mode(9)
• enum ethtool_c33_pse_ext_state(9)
• enum ethtool_c33_pse_ext_substate_mr_mps_valid(9)
• enum ethtool_c33_pse_ext_substate_error_condition(9)
• enum ethtool_c33_pse_ext_substate_mr_pse_enable(9)
• enum ethtool_c33_pse_ext_substate_option_detect_ted(9)
• enum ethtool_c33_pse_ext_substate_option_vport_lim(9)
• enum ethtool_c33_pse_ext_substate_ovld_detected(9)
• enum ethtool_c33_pse_ext_substate_power_not_available(9)
• enum ethtool_c33_pse_ext_substate_short_detected(9)
• enum ethtool_pse_types(9)
• enum ethtool_c33_pse_admin_state(9)
• enum ethtool_c33_pse_pw_d_status(9)
• enum ethtool_podl_pse_admin_state(9)
• enum ethtool_podl_pse_pw_d_status(9)
• enum ethtool_mm_verify_status(9)
• enum ethtool_module_fw_flash_status(9)
• struct ethtool_gstrings(9)
• struct ethtool_sset_info(9)
• enum ethtool_test_flags(9)
• struct ethtool_stats(9)
• struct ethtool_perm_addr(9)
• struct ethtool_tcpip4_spec(9)
• struct ethtool_ah_espip4_spec(9)
• struct ethtool_usrip4_spec(9)
• struct ethtool_tcpip6_spec(9)
• struct ethtool_ah_espip6_spec(9)
• struct ethtool_usrip6_spec(9)
• struct ethtool_flow_ext(9)
• struct ethtool_rx_flow_spec(9)
• struct ethtool_rxnfc(9)
• struct ethtool_rxfh_indir(9)
• struct ethtool_rxfh(9)
• struct ethtool_rx_ntuple_flow_spec(9)
• struct ethtool_rx_ntuple(9)
• struct ethtool_dump(9)
• struct ethtool_get_features_block(9)
• struct ethtool_gfeatures(9)
• struct ethtool_set_features_block(9)
• struct ethtool_sfeatures(9)
• struct ethtool_ts_info(9)
• struct ethtool_per_queue_op(9)
• struct ethtool_fecparam(9)
• enum ethtool_fec_config_bits(9)
• struct ethtool_link_settings(9)
• enum phy_upstream(9)

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And that's the whole page, bestie! 🧚 Signing off from ./include/uapi/linux, dated October 2026 — go run that self-test, allocate 8 * number of results bytes right after the struct, and slay 💖✨