io_uring_register_zcrx_ctrl(3)

✨ io_uring_register_zcrx_ctrl ✨

okay bestie, welcome to the liburing Manual 💖 this one's a lil deep in the weeds but we're gonna get through it together, i promise.

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🎀 NAME 🎀

io_uring_register_zcrx_ctrl — does control operations on a zero-copy receive context. that's it, that's the whole vibe 💅

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🦋 SYNOPSIS 🦋

#include <liburing.h>

int io_uring_register_zcrx_ctrl(struct io_uring *ring,
                                struct zcrx_ctrl *ctrl);

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🌸 DESCRIPTION 🌸

so io_uring_register_zcrx_ctrl(3) performs control operations on a zero-copy receive context that you already registered earlier. if you wanna know how to register one of those in the first place, go look at io_uring_register_ifq(3), she explains it 🫶

the ctrl argument has to point at a struct zcrx_ctrl structure that describes which control operation you want:

struct zcrx_ctrl {
    __u32 zcrx_id;
    __u32 op;
    __u64 __resv[2];
    union {
        struct zcrx_ctrl_export     zc_export;
        struct zcrx_ctrl_flush_rq   zc_flush;
    };
};

k so the zcrx_id field? that MUST be set to the ID of the zero-copy receive context that io_uring_register_ifq(3) handed back to you. no guessing, use the one you got 💅

then the op field is the actual "what are we doing today" field, and it can be one of these two iconic options:

• ZCRX_CTRL_FLUSH_RQ — flushes the pending buffers out of the refill queue. this one uses the zc_flush member of the union. it's giving tidy up ✨
• ZCRX_CTRL_EXPORT — exports the zero-copy receive context so other rings can use it. this one uses the zc_export member of the union. and bestie, once the export succeeds, the zcrx_fd field inside zc_export will hold the file descriptor you can use to share this context with other io_uring instances. that's the whole point, that's the moment 👑

⚠️ and the reserved __resv fields? clear them to zero. all of them. don't leave crumbs, don't leave vibes, just zeros 😭

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⭐ RETURN VALUE ⭐

• returns 0 when it works 🎉
• on error it returns a negative errno value. classic.

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🌈 NOTES 🌈

this function has been available since Linux kernel 6.15. so if you're on an older kernel, bestie... she's not there yet 😭

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🧚 SEE ALSO 🧚

• io_uring_register(2)
• io_uring_register_ifq(3)

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and that's the whole page, periodt 💖 this lil writeup is from liburing-2.15, dated March 26, 2026 — go forth and register your zero-copy receive contexts responsibly, queen 👑✨