在 Linux 下创建 WiFi 热点 (Access Point)，自古以来都不是一件容易的事情。

常见的解决方案有三种，hostapd、NetworkManager 和 systemd-networkd。

前两种方案用的比较多，而 systemd 近些年才在服务器中流行起来，文档和教程相对而言比较少。

一般而言，使用 NetworkManager 可以获得“开箱即用”的体验——但只能说勉强能用，存在的问题也很多。比如，5GHz 往往不能工作、不能指定频宽等等……

hostapd 则提供了许多配置项，但代价是配置非常复杂。好在有一些现成的配置文件和脚本可以参考，比如USB-WiFi、create_ap、linux-wifi-hotspot 和 linux-router。

使用 5GHz 频段

网上的教程一般只涉及 2.4GHz 的配置。一开始，我以为只需要把 802.11n 改成 802.11ac，再调整一下频段就可以了。然而，现实却狠狠地打了我的脸：

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2月 26 14:45:16 armbian wpa_supplicant[1107]: nl80211: Added 802.11b mode based on 802.11g information
2月 26 14:45:16 armbian wpa_supplicant[1107]: nl80211: Mode IEEE 802.11g: 2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467[NO_IR] 2472 2484[NO_IR]
2月 26 14:45:16 armbian wpa_supplicant[1107]: nl80211: Mode IEEE 802.11a: 5180 5200[NO_IR] 5220 5240[NO_IR] 5260[NO_IR][RADAR] 5280[NO_IR][RADAR] 5300[NO_IR][RADAR] 5320[NO_IR][RADAR] 5500[NO_IR][RADAR] 5520[NO_IR][RADAR] 5540[NO_IR][RADAR] 5560[NO_IR][RADAR]
2月 26 14:45:16 armbian wpa_supplicant[1107]: nl80211: Mode IEEE 802.11b: 2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467[NO_IR] 2472 2484[NO_IR]
2月 26 14:45:16 armbian wpa_supplicant[1107]: Frequency 5280 (primary) not allowed for AP mode, flags: 0x117b NO-IR RADAR
2月 26 14:45:16 armbian wpa_supplicant[1107]: Primary frequency not allowed
2月 26 14:45:16 armbian wpa_supplicant[1107]: hostapd_logger: Configured channel (56) or frequency (5280) (secondary_channel=0) not found from the channel list of the current mode (2) IEEE 802.11a
2月 26 14:45:16 armbian wpa_supplicant[1107]: hostapd_logger: Hardware does not support configured channel
2月 26 14:45:16 armbian wpa_supplicant[1107]: Could not select hw_mode and channel. (-3)
2月 26 14:45:16 armbian wpa_supplicant[1107]: wlan0: interface state UNINITIALIZED->DISABLED
2月 26 14:45:16 armbian wpa_supplicant[1107]: wlan0: AP-DISABLED
2月 26 14:45:16 armbian wpa_supplicant[1107]: wlan0: Unable to setup interface.
2月 26 14:45:16 armbian wpa_supplicant[1107]: Failed to initialize AP interface
2月 26 14:45:16 armbian wpa_supplicant[1107]: hostapd_interface_deinit(0x55a8bcff50)
2月 26 14:45:16 armbian wpa_supplicant[1107]: wlan0: interface state DISABLED->DISABLED

看起来是指定了网卡不支持的频段！使用 iw list 查看一下支持的频段：

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❯ sudo iw list
......
Band 1:
    Frequencies:
        * 2412 MHz [1] (20.0 dBm)
        * 2417 MHz [2] (20.0 dBm)
        * 2422 MHz [3] (20.0 dBm)
        * 2427 MHz [4] (20.0 dBm)
        * 2432 MHz [5] (20.0 dBm)
        * 2437 MHz [6] (20.0 dBm)
        * 2442 MHz [7] (20.0 dBm)
        * 2447 MHz [8] (20.0 dBm)
        * 2452 MHz [9] (20.0 dBm)
        * 2457 MHz [10] (20.0 dBm)
        * 2462 MHz [11] (20.0 dBm)
        * 2467 MHz [12] (20.0 dBm) (no IR)
        * 2472 MHz [13] (20.0 dBm)
        * 2484 MHz [14] (20.0 dBm) (no IR)
......
Band 2:
    Frequencies:
        * 5180 MHz [36] (20.0 dBm)
        * 5200 MHz [40] (20.0 dBm) (no IR)
        * 5220 MHz [44] (20.0 dBm)
        * 5240 MHz [48] (20.0 dBm) (no IR)
        * 5260 MHz [52] (20.0 dBm) (no IR, radar detection)
        * 5280 MHz [56] (20.0 dBm) (no IR, radar detection)
        * 5300 MHz [60] (20.0 dBm) (no IR, radar detection)
        * 5320 MHz [64] (20.0 dBm) (no IR, radar detection)
        * 5500 MHz [100] (20.0 dBm) (no IR, radar detection)
        * 5520 MHz [104] (20.0 dBm) (no IR, radar detection)
        * 5540 MHz [108] (20.0 dBm) (no IR, radar detection)
        * 5560 MHz [112] (20.0 dBm) (no IR, radar detection)
        * 5580 MHz [116] (20.0 dBm) (no IR, radar detection)
        * 5600 MHz [120] (20.0 dBm) (no IR, radar detection)
        * 5620 MHz [124] (20.0 dBm) (no IR, radar detection)
        * 5640 MHz [128] (20.0 dBm) (no IR, radar detection)
        * 5660 MHz [132] (20.0 dBm) (no IR, radar detection)
        * 5680 MHz [136] (20.0 dBm) (no IR, radar detection)
        * 5700 MHz [140] (20.0 dBm) (no IR, radar detection)
        * 5720 MHz [144] (20.0 dBm) (no IR, radar detection)
        * 5745 MHz [149] (20.0 dBm)
        * 5765 MHz [153] (20.0 dBm) (no IR)
        * 5785 MHz [157] (20.0 dBm)
        * 5805 MHz [161] (20.0 dBm) (no IR)
        * 5825 MHz [165] (20.0 dBm) (no IR)

好家伙，几乎所有的 5GHz 信道都被标记了 no IR (no-initiating-radiation)，也就是无法使用！

根据 Arch Linux wiki 的说法，每个国家都有着不同的限制，因此我们可以通过设置国家代码来规避这种限制：

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❯ sudo iw reg get
global
country 00: DFS-UNSET
        (2402 - 2472 @ 40), (6, 20), (N/A)
        (2457 - 2482 @ 20), (6, 20), (N/A), AUTO-BW, PASSIVE-SCAN
        (2474 - 2494 @ 20), (6, 20), (N/A), NO-OFDM, PASSIVE-SCAN
        (5170 - 5250 @ 80), (6, 20), (N/A), AUTO-BW, PASSIVE-SCAN
        (5250 - 5330 @ 80), (6, 20), (0 ms), DFS, AUTO-BW, PASSIVE-SCAN
        (5490 - 5730 @ 160), (6, 20), (0 ms), DFS, PASSIVE-SCAN
        (5735 - 5835 @ 80), (6, 20), (N/A), PASSIVE-SCAN
        (57240 - 63720 @ 2160), (N/A, 0), (N/A)

❯ sudo iw reg set CN

❯ sudo iw reg get
global
country 00: DFS-UNSET
        (2402 - 2472 @ 40), (6, 20), (N/A)
        (2457 - 2482 @ 20), (6, 20), (N/A), AUTO-BW, PASSIVE-SCAN
        (2474 - 2494 @ 20), (6, 20), (N/A), NO-OFDM, PASSIVE-SCAN
        (5170 - 5250 @ 80), (6, 20), (N/A), AUTO-BW, PASSIVE-SCAN
        (5250 - 5330 @ 80), (6, 20), (0 ms), DFS, AUTO-BW, PASSIVE-SCAN
        (5490 - 5730 @ 160), (6, 20), (0 ms), DFS, PASSIVE-SCAN
        (5735 - 5835 @ 80), (6, 20), (N/A), PASSIVE-SCAN
        (57240 - 63720 @ 2160), (N/A, 0), (N/A)

怎么回事？为什么国家代码的设置没有生效？就在我一筹莫展时，我无意间发现了这个issue。
按照 issue 中的 workaround，将 regulatory.db链接到 /lib/firmware/regulatory.db-upstream后，出乎意料的可以工作了：

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❯ dmesg | grep -i cfg80211
[   13.255344] cfg80211: Loading compiled-in X.509 certificates for regulatory database
❯ sudo iw reg get
global
country US: DFS-FCC
        (902 - 904 @ 2), (N/A, 30), (N/A)
        (904 - 920 @ 16), (N/A, 30), (N/A)
        (920 - 928 @ 8), (N/A, 30), (N/A)
        (2400 - 2472 @ 40), (N/A, 30), (N/A)
        (5150 - 5250 @ 80), (N/A, 23), (N/A), AUTO-BW
        (5250 - 5350 @ 80), (N/A, 24), (0 ms), DFS, AUTO-BW
        (5470 - 5730 @ 160), (N/A, 24), (0 ms), DFS
        (5730 - 5850 @ 80), (N/A, 30), (N/A), AUTO-BW
        (5850 - 5895 @ 40), (N/A, 27), (N/A), NO-OUTDOOR, AUTO-BW, PASSIVE-SCAN
        (5925 - 7125 @ 320), (N/A, 12), (N/A), NO-OUTDOOR, PASSIVE-SCAN
        (57240 - 71000 @ 2160), (N/A, 40), (N/A)
❯ sudo iw list
......
Band 2:
    Frequencies:
        * 5180 MHz [36] (23.0 dBm)
        * 5200 MHz [40] (23.0 dBm)
        * 5220 MHz [44] (23.0 dBm)
        * 5240 MHz [48] (23.0 dBm)
        * 5260 MHz [52] (24.0 dBm) (radar detection)
        * 5280 MHz [56] (24.0 dBm) (radar detection)
        * 5300 MHz [60] (24.0 dBm) (radar detection)
        * 5320 MHz [64] (24.0 dBm) (radar detection)
        * 5500 MHz [100] (24.0 dBm) (radar detection)
        * 5520 MHz [104] (24.0 dBm) (radar detection)
        * 5540 MHz [108] (24.0 dBm) (radar detection)
        * 5560 MHz [112] (24.0 dBm) (radar detection)
        * 5580 MHz [116] (24.0 dBm) (radar detection)
        * 5600 MHz [120] (24.0 dBm) (radar detection)
        * 5620 MHz [124] (24.0 dBm) (radar detection)
        * 5640 MHz [128] (24.0 dBm) (radar detection)
        * 5660 MHz [132] (24.0 dBm) (radar detection)
        * 5680 MHz [136] (24.0 dBm) (radar detection)
        * 5700 MHz [140] (24.0 dBm) (radar detection)
        * 5720 MHz [144] (24.0 dBm) (radar detection)
        * 5745 MHz [149] (33.0 dBm)
        * 5765 MHz [153] (33.0 dBm)
        * 5785 MHz [157] (33.0 dBm)
        * 5805 MHz [161] (33.0 dBm)
        * 5825 MHz [165] (33.0 dBm)

开启 80MHz 频宽

一通操作猛如虎，一测速度二百五。

按照linux-router中的教程，只需要指定 ssid 和 password 就可以开启热点：

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sudo lnxrouter --ap wlan0 <ssid> -p <password> --freq-band 5 --wifi5

这样虽然能开启热点，但尴尬的是它的频宽只有 20MHz，并且握手速度只有 54Mbps（还不如直接去用 802.11n 呢）

在中国，52-68 信道被划为 DFS 信道，而 96-144 信道则不允许使用。参考：List_of_WLAN_channels

使用 DFS 信道时，按照法规要求，启动时应先检测附近是否有雷达信号，在使用过程中如果检测到了雷达信号也必须进行规避。这会导致热点启动延迟，并带来诸多难以排查的奇怪问题。反正尽量别用就对了！

更重要的是，我的网卡在 DFS 信道上的发射功率远低于其他信道。因此，我们将使用其他信道。尝试指定 149 信道并启用 80MHz 频宽：

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sudo lnxrouter --ap wlan0 <ssid> -p <password> --freq-band 5 -c 149 --country CN --wifi5 --req-vht --vht-ch-width 1

不出意外的话，这时 hostapd 会输出一长串日志，告诉你启动失败了：

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ctrl_interface_group=0
nl80211: TDLS supported
nl80211: TDLS external setup
nl80211: Supported cipher 00-0f-ac:1
nl80211: Supported cipher 00-0f-ac:5
nl80211: Supported cipher 00-0f-ac:2
nl80211: Supported cipher 00-0f-ac:4
nl80211: Supported cipher 00-0f-ac:10
nl80211: Supported cipher 00-0f-ac:8
nl80211: Supported cipher 00-0f-ac:9
nl80211: Supported cipher 00-0f-ac:6
nl80211: Supported cipher 00-0f-ac:13
nl80211: Supported cipher 00-0f-ac:11
nl80211: Supported cipher 00-0f-ac:12
nl80211: Using driver-based off-channel TX
nl80211: Driver-advertised extended capabilities (default) - hexdump(len=8): 00 00 00 00 00 00 00 40
nl80211: Driver-advertised extended capabilities mask (default) - hexdump(len=8): 00 00 00 00 00 00 00 40
nl80211: Use separate P2P group interface (driver advertised support)
nl80211: key_mgmt=0x1ff0f enc=0xfef auth=0x7 flags=0x240005105b1bfae0 rrm_flags=0x30 probe_resp_offloads=0x0 max_stations=0 max_remain_on_chan=5000 max_scan_ssids=4
nl80211: interface x2wlan0 in phy phy1
nl80211: Set mode ifindex 51 iftype 3 (AP)
nl80211: Setup AP(x2wlan0) - device_ap_sme=0 use_monitor=0
nl80211: Subscribe to mgmt frames with AP handle 0x55a682cb70
nl80211: Register frame type=0xb0 (WLAN_FC_STYPE_AUTH) nl_handle=0x55a682cb70 match= multicast=0
nl80211: Register frame type=0x0 (WLAN_FC_STYPE_ASSOC_REQ) nl_handle=0x55a682cb70 match= multicast=0
nl80211: Register frame type=0x20 (WLAN_FC_STYPE_REASSOC_REQ) nl_handle=0x55a682cb70 match= multicast=0
nl80211: Register frame type=0xa0 (WLAN_FC_STYPE_DISASSOC) nl_handle=0x55a682cb70 match= multicast=0
nl80211: Register frame type=0xc0 (WLAN_FC_STYPE_DEAUTH) nl_handle=0x55a682cb70 match= multicast=0
nl80211: Register frame type=0x40 (WLAN_FC_STYPE_PROBE_REQ) nl_handle=0x55a682cb70 match= multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=04 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=0501 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=0503 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=0504 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=06 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=08 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=09 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=0a multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=11 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=12 multicast=0
nl80211: Register frame type=0xd0 (WLAN_FC_STYPE_ACTION) nl_handle=0x55a682cb70 match=7f multicast=0
rfkill: initial event: idx=2 type=1 op=0 soft=0 hard=0
nl80211: Add own interface ifindex 51 (ifidx_reason -1)
nl80211: if_indices[16]: 51(-1)
nl80211: Do not open EAPOL RX socket - using control port for RX
phy: phy1
BSS count 1, BSSID mask 00:00:00:00:00:00 (0 bits)
x2wlan0: interface state UNINITIALIZED->COUNTRY_UPDATE
Previous country code CN, new country code CN
nl80211: Regulatory information - country=CN (DFS-FCC)
nl80211: 2400-2483 @ 40 MHz 20 mBm
nl80211: 5150-5350 @ 80 MHz 20 mBm (DFS)
nl80211: 5725-5850 @ 80 MHz 33 mBm
nl80211: 57240-59400 @ 2160 MHz 28 mBm
nl80211: 59400-63720 @ 2160 MHz 44 mBm
nl80211: 63720-65880 @ 2160 MHz 28 mBm
nl80211: Added 802.11b mode based on 802.11g information
nl80211: Mode IEEE 802.11g: 2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467 2472 2484[DISABLED][NO_IR]
nl80211: Mode IEEE 802.11a: 5180[RADAR] 5200[RADAR] 5220[RADAR] 5240[RADAR] 5260[RADAR] 5280[RADAR] 5300[RADAR] 5320[RADAR] 5500[DISABLED][RADAR] 5520[DISABLED][RADAR] 5540[DISABLED][RADAR] 5560[DISABLED][RADAR]
nl80211: Mode IEEE 802.11b: 2412 2417 2422 2427 2432 2437 2442 2447 2452 2457 2462 2467 2472 2484[DISABLED][NO_IR]
Allowed channel: mode=1 chan=1 freq=2412 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=2 freq=2417 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=3 freq=2422 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=4 freq=2427 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=5 freq=2432 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=6 freq=2437 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=7 freq=2442 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=8 freq=2447 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=9 freq=2452 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=10 freq=2457 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=11 freq=2462 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=12 freq=2467 MHz max_tx_power=20 dBm
Allowed channel: mode=1 chan=13 freq=2472 MHz max_tx_power=20 dBm
Allowed channel: mode=2 chan=149 freq=5745 MHz max_tx_power=33 dBm
Allowed channel: mode=2 chan=153 freq=5765 MHz max_tx_power=33 dBm
Allowed channel: mode=2 chan=157 freq=5785 MHz max_tx_power=33 dBm
Allowed channel: mode=2 chan=161 freq=5805 MHz max_tx_power=33 dBm
Allowed channel: mode=2 chan=165 freq=5825 MHz max_tx_power=33 dBm
Allowed channel: mode=0 chan=1 freq=2412 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=2 freq=2417 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=3 freq=2422 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=4 freq=2427 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=5 freq=2432 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=6 freq=2437 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=7 freq=2442 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=8 freq=2447 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=9 freq=2452 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=10 freq=2457 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=11 freq=2462 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=12 freq=2467 MHz max_tx_power=20 dBm
Allowed channel: mode=0 chan=13 freq=2472 MHz max_tx_power=20 dBm
Completing interface initialization
Mode: IEEE 802.11a  Channel: 149  Frequency: 5745 MHz
DFS chan_idx seems wrong; num-ch: 25 ch-no: -6 conf-ch-no: 149 11n: 0 sec-ch: 0 vht-oper-width: 1
Available channel: 36
Available channel: 40
Available channel: 44
Available channel: 48
Available channel: 52
Available channel: 56
Available channel: 60
Available channel: 64
Available channel: 100
Available channel: 104
Available channel: 108
Available channel: 112
Available channel: 116
Available channel: 120
Available channel: 124
Available channel: 128
Available channel: 132
Available channel: 136
Available channel: 140
Available channel: 144
Available channel: 149
Available channel: 153
Available channel: 157
Available channel: 161
Available channel: 165
Interface initialization failed
x2wlan0: interface state COUNTRY_UPDATE->DISABLED
x2wlan0: AP-DISABLED
x2wlan0: Unable to setup interface.
hostapd_interface_deinit_free(0x55a682aa30)
hostapd_interface_deinit_free: num_bss=1 conf->num_bss=1
hostapd_interface_deinit(0x55a682aa30)
x2wlan0: interface state DISABLED->DISABLED
hostapd_bss_deinit: deinit bss x2wlan0
x2wlan0: Deauthenticate all stations
nl80211: send_mlme - da=ff:ff:ff:ff:ff:ff noack=0 freq=0 no_cck=0 offchanok=0 wait_time=0 no_encrypt=0 fc=0xc0 (WLAN_FC_STYPE_DEAUTH) nlmode=3
nl80211: send_mlme - Use bss->freq=0
nl80211: send_mlme -> send_frame_cmd
nl80211: CMD_FRAME freq=0 wait=0 no_cck=0 no_ack=0 offchanok=0
CMD_FRAME - hexdump(len=26): c0 00 00 00 ff ff ff ff ff ff 0c 91 60 7f 02 1e 0c 91 60 7f 02 1e 00 00 03 00
nl80211: Frame command failed: ret=-22 (Invalid argument) (freq=0 wait=0)
x2wlan0: AP-DISABLED
hostapd_cleanup(hapd=0x55a682da10 (x2wlan0))
x2wlan0: CTRL-EVENT-TERMINATING
hostapd_free_hapd_data: Interface x2wlan0 wasn't started
hostapd_interface_deinit_free: driver=0x55746ee5a0 drv_priv=0x55a682ffd0 -> hapd_deinit
nl80211: deinit ifname=x2wlan0 disabled_11b_rates=0
nl80211: Remove monitor interface: refcount=0
nl80211: Remove beacon (ifindex=51)
netlink: Operstate: ifindex=51 linkmode=0 (kernel-control), operstate=6 (IF_OPER_UP)
nl80211: Set mode ifindex 51 iftype 2 (STATION)
nl80211: Failed to set interface 51 to mode 2: -16 (Device or resource busy)
nl80211: Try mode change after setting interface down
nl80211: Set mode ifindex 51 iftype 2 (STATION)
nl80211: Mode change succeeded while interface is down
nl80211: Teardown AP(x2wlan0) - device_ap_sme=0 use_monitor=0
nl80211: Unsubscribe mgmt frames handle 0x888888dd2e0a43f9 (AP teardown)
hostapd_interface_free(0x55a682aa30)
hostapd_interface_free: free hapd 0x55a682da10
hostapd_cleanup_iface(0x55a682aa30)
hostapd_cleanup_iface_partial(0x55a682aa30)
hostapd_cleanup_iface: free iface=0x55a682aa30

它告诉我们没有指定中心频率（vht_oper_centr_freq_seg0_idx）：

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DFS chan_idx seems wrong; num-ch: 25 ch-no: -6 conf-ch-no: 149 11n: 0 sec-ch: 0 vht-oper-width: 1

查看配置文件，可以看到我们确实没有指定 vht_oper_centr_freq_seg0_idx：

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❯ sudo cat /dev/shm/lnxrouter_tmp/lnxrouter.wlan0.conf*/hostapd.conf
beacon_int=100
ssid=ssid
interface=x0wlan0
driver=nl80211
channel=149
ctrl_interface=/dev/shm/lnxrouter_tmp/lnxrouter.wlan0.conf.vRBiOQ/hostapd_ctrl
ctrl_interface_group=0
ignore_broadcast_ssid=0
ap_isolate=0
country_code=CN
ieee80211d=1
hw_mode=a
ieee80211ac=1
vht_oper_chwidth=1
wmm_enabled=1
wpa=2
wpa_passphrase=password
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
rsn_pairwise=CCMP

对于 80MHz 频宽，vht_oper_centr_freq_seg0_idx的值一般是 channel+6。
然而，lnxrouter 并没有提供指定 vht_oper_centr_freq_seg0_idx的选项，我采用了一个比较 dirty 的方法——直接修改 lnxrouter 的脚本文件： 眼瞎了，可以通过 --vht-seg0-ch 参数指定

再次执行脚本，hostapd 会出现新的报错：

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DFS 0 channels required radar detection
80/80+80 MHz: no second channel offset
Could not set channel for kernel driver

这是由于我们没有设置合适的 ht_capab 或 vht_capab 导致的。
参考hostapd-WiFi5.conf，添加合适的 capability 到 lnxrouter 中：

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sudo lnxrouter --ap wlan0 <ssid> -p <password> --freq-band 5 -c 149 --country CN --ieee80211n --ieee80211ac --ht-capab "[HT40+][HT40-][SHORT-GI-20][SHORT-GI-40][MAX-AMSDU-7935]" --vht-capab "[MAX-MPDU-11454][SHORT-GI-80][TX-STBC-2BY1][SU-BEAMFORMEE][HTC-VHT]" --vht-ch-width 1

Tips:
ht_capab 和 vht_capab 的值取决于驱动程序，不同的驱动程序支持的参数可能不同。对于 rtw88 驱动，上述的 capability 应该可以正常工作。

Tips:
我并不清楚这些 capability 的作用，于是我让 GPT 解释了一下：

802.11n 功能：

  • HT40+ 和 HT40-：支持 40 MHz 信道宽度。+ 或 - 表示 AP 使用 40 MHz 信道的上/下 20 MHz 部分。40 MHz 信道比 20 MHz 吞吐量更高。
  • SHORT-GI-20：启用 20 MHz 信道的短保护间隔（SGI）。保护间隔是符号间的静默时间，用于避免信号重叠。短保护间隔减少静默时间，提升信道效率。
  • SHORT-GI-40：同上，但适用于 40 MHz 信道，可减少开销并提升吞吐量。
  • GF（Greenfield 模式）：启用 纯 802.11n 模式（不兼容传统非 HT 设备）。此模式通过放弃向后兼容性来提高效率（现代网络较少使用）。
  • MAX-AMSDU-7935：
    设置 最大聚合 MAC 服务数据单元（AMSDU）大小，允许 AP 发送更大的数据包以减少开销。

802.11ac 功能：

  • SHORT-GI-80：启用 80 MHz 信道的短保护间隔，减少静默时间以提升吞吐量。
  • MAX-MPDU-11454：设置 最大 MPDU（MAC 协议数据单元）大小，更大的 MPDU 可提升效率。
  • TX-STBC-2BY1：启用 发射端空时块编码（STBC），通过多天线提升多径环境下的信号稳定性。
  • RX-STBC-1：启用 接收端 STBC（支持单空间流）。
  • SU-BEAMFORMEE：支持 单用户波束成形，AP 将信号定向传输至特定设备，提升信号质量与覆盖范围。
  • MU-BEAMFORMEE：支持 多用户波束成形，AP 可同时定向传输至多个设备。
  • HTC-VHT：
    支持 802.11ac 的 高吞吐量控制信道模式。

不出意外的话，此时热点已经工作在 80MHz 的频宽下，并且握手速度也应该达到 433/866Mbps。
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后记

在 Linux 下创建 AP 确实不是一件容易的事。如果不是特殊需求，使用 OpenWrt 这种为无线专门优化过的发行版，可能会是更好的选择。