fgraph_reserve_data(9)

✨ fgraph_reserve_data ✨

okay so bestie, welcome to fgraph_reserve_data — that's a section 9 (kernel API) manual page, and yes it's giving "we're doing kernel tracing today" 🎀

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🌸 NAME 🌸

fgraph_reserve_data — reserve storage on the task's ret_stack, no cap 💅

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🦋 SYNOPSIS 🦋

void * fgraph_reserve_data (int idx , int size_bytes );

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🍓 ARGUMENTS 🍓

• idx — the index of fgraph_array. that's it, that's the whole vibe.
• size_bytes — the size in bytes to reserve. literally how much space you want, in bytes 👑

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💜 DESCRIPTION 💜

so here's the tea ☕ — this function reserves space of up to FGRAPH_MAX_DATA_SIZE bytes on the task's ret_stack shadow stack, for a given fgraph_ops, during the entryfunc call. iconic behaviour honestly.

if entryfunc returns zero, the storage is discarded — like, gone, poof, never happened 😭

an entryfunc can only call this once per iteration. one. single. time. don't be greedy babes 🙈

the fgraph_ops retfunc can then retrieve this stored data with fgraph_retrieve_data. cute little hand-off, we love to see it 🫶

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🔥 RETURN 🔥

on success, you get a pointer to the data on the stack ✨

otherwise? NULL 😭 and there's two reasons that can happen:

• there's not enough space left on the ret_stack for the data
• or fgraph_reserve_data was called more than once for a single entryfunc call (told you — once per iteration, bestie 💀)

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👑 SEE ALSO 👑

• the kernel file ./kernel/trace/fgraph.c
• fgraph_retrieve_data(9)
• fgraph_get_task_var(9)
• fgraph_retrieve_parent_data(9)
• ftrace_graph_stop(9)
• ftrace_graph_get_ret_stack(9)
• ftrace_graph_top_ret_addr(9)
• ftrace_graph_ret_addr(9)

go read them, they're all main character energy fr fr 🌈

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and that's the whole page!! this little icon lives in ./kernel/trace, dated October 2026, part of the Kernel API Manual. mwah, slay, periodt 💖💅🎀