docs/designs/sol-sysrq.md

11 [SysRq][1] is a special key combination used by Linux to perform various
12 low-level commands. BMC usually provides SysRq support in KVM and SOL functions,
18 The key combination consists of Alt+SysRq (usually the `PrintScreen` key) and
19 another key, which controls the command issued. This is not typical key code and
21 sending a serial break signal, followed by the desired key. The "break signal"
22 is usually generated by `ctrl+break` key combination.[2]
31 - The ipmitool SOL.
32 - The SOL in WebUI.
33 - The console with SSH (default) 2200 port.
37 In OpenBMC, the service `obmc-console-server` provides the host console and
40 To implement the SysRq in OpenBMC SOL for ipmi and WebUI, the special key code
42 console-server. In `obmc-console`, a state machine shall handle the sequence.
48 In `phosphor-ipmi-net`, the code in `processInboundPayload()` shall handle the
57 key code sequence `\n~B` to trigger the break, and then user could enter a
60 ### obmc-console
62 As the obmc-console server, in `console-server.h`, a simple state machine is
66 ---
68 ---
69 stateDiagram-v2
70     [*] --> Empty
71     Empty --> Emit: [^#92;n]
72     Emit --> [*]
73     Empty --> Newline: [#92;n]
74     Newline --> Escape: [~]
75     Newline --> EmitNewline: [^#92;n]
76     Escape --> EmitEscapeCode: [B]
77     EmitEscapeCode --> [*]
78     EmitNewline --> [*]
79     Escape --> EmitNewlineTilde: [^B]
80     EmitNewlineTilde --> [*]
88 An alternative way to send the "break signal" between clients and console-server
91 modified to send `MSG_OOB` to obmc-console when the user enter the key code
92 sequence `\n~B`. When obmc-console receive `MSG_OOB`, it shall send the "break
95 However, in this solution, in some scenarios, obmc-console can not handle the
98 [sockatmark(3)][5]. But it requires signalling the `MSG_OOB` in all obmc-console
105 - netipmid
106 - obmc-console
111 with SSH, we need enter the key code sequence with more than one tilde. Like
112 sequence `\n~~B`, the first tilde will be processed by obmc-console-client, the
113 second tilde will reach obmc-console-server.
116 [2]: https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html
117 [3]: https://github.com/ipmitool/ipmitool/blob/master/lib/ipmi_sol.c#L1398-L1401
119   https://github.com/openbmc/phosphor-net-ipmid/commit/ec4374146147e339132243725d345eb30ec2da1d
120 [5]: https://man7.org/linux/man-pages/man3/sockatmark.3.html