TIME TRAVEL SHARED MEMORY OVERVIEW(9)

💖 TIME TRAVEL SHARED MEMORY OVERVIEW 💖

okay so welcome to Time travel shared memory overview(9) from the Kernel API Manual, section 9 — and bestie, this page is literally about the shared-memory setup that keeps time-travel messages from being extra. 🦋

✨ DESCRIPTION ✨

The main purpose of the shared memory is to avoid all time travel messages that don’t need any action. Like, current time can be held in shared memory without any client needing to send a message UM_TIMETRAVEL_GET just to know what the time is. No cap. ⭐

Since this is shared memory with all clients and the controller, and the controller creates the shared memory space, all time values are absolute to controller time. So the first time a client connects to shared memory mode, it should take the current_time value in shared memory and keep it internally as a diff to shared memory times. And once shared memory is initialized, any interaction with the controller must happen in the controller time domain, including any messages. (For clients that are not using shared memory, the controller will handle an offset and make the clients think they start at time zero.) 🫶

Along with the shared memory file descriptor, a logging file descriptor is sent to the client, so all logs related to shared memory get logged into one place. 📝

note: to have all logs synced into the log file at write, the file should be flushed (fflush) after writing to it. 💅

To avoid memory corruption, we define below, for each field, who can write to it at what time, defined in the structure fields. This is the safety vibe check, fr fr. 🔥

To avoid having to pack this struct, all fields in it must be naturally aligned (i.e. aligned to their size). periodt. ✨

🔗 SEE ALSO 🔗

• Kernel file ./include/uapi/linux/um_timetravel.h struct
• um_timetravel_msg(9)
• enum um_timetravel_shared_mem_fds(9)
• enum um_timetravel_start_ack(9)
• enum um_timetravel_ops(9)
• enum um_timetravel_schedshm_cap(9)
• enum um_timetravel_schedshm_flags(9)
• union um_timetravel_schedshm_client(9)
• struct um_timetravel_schedshm(9)

and that’s the whole vibe, bestie 🎀 — source: ./include/uapi/linux, date: October 2026, from the Time travel ...ory overview(9) page. slay 💅