io\_uring\_register\_region(3) liburing Manual io\_uring\_register\_region(3)

# [NAME](#NAME)

io\_uring\_register\_region - register a memory region

# [SYNOPSIS](#SYNOPSIS)

```
#include <liburing.h>
```

```
int io_uring_register_region(struct io_uring *ring,
                             struct io_uring_mem_region_reg *reg);
```

# [DESCRIPTION](#DESCRIPTION)

The [**io\_uring\_register\_region**(3)](/man/os/liburing/io_uring_register_region.3) function registers a memory region to io\_uring. Upon successful completion, the memory region may then be used, for example, to pass waiting parameters to the [**io\_uring\_enter**(2)](/man/os/liburing/io_uring_enter.2) system call in a more efficient manner as it avoids copying wait related data for each wait event. The *ring* argument should point to the ring in question, and the *reg* argument should be a pointer to a **struct io\_uring\_mem\_region\_reg .**

The *reg* argument must be filled in with the appropriate information. It looks as follows:

```
struct io_uring_mem_region_reg {


    __u64 region_uptr;


    __u64 flags;


    __u64 __resv[2];
};
```

The *region\_uptr* field must contain a pointer to an appropriately filled **struct io\_uring\_region\_desc.**

The *flags* field must contain a bitmask of the following values:

[**IORING\_MEM\_REGION\_REG\_WAIT\_ARG**](#IORING_MEM_REGION_REG_WAIT_ARG)

allows use of the region to pass waiting parameters to the [**io\_uring\_enter**(2)](/man/os/liburing/io_uring_enter.2) system call. If set, the registration is only allowed while the ring is in a disabled mode. See **IORING\_SETUP\_R\_DISABLED.**

The \_\_resv fields must be filled with zeroes.

**struct io\_uring\_region\_desc** is defined as following:

```
struct io_uring_region_desc {


    __u64 user_addr;


    __u64 size;


    __u32 flags;


    __u32 id;


    __u64 mmap_offset;


    __u64 __resv[4];
};
```

The *user\_addr* field must contain a pointer to the memory the user wants to register. It's valid only if **IORING\_MEM\_REGION\_TYPE\_USER** is set, and should be zero otherwise.

The *size* field should contain the size of the region.

The *flags* field must contain a bitmask of the following values:

[**IORING\_MEM\_REGION\_TYPE\_USER**](#IORING_MEM_REGION_TYPE_USER)

tells the kernel to use memory specified by the *user\_addr* field. If not set, the kernel will allocate memory for the region, which can then be mapped into the user space.

On successful registration of a region with kernel provided memory, the *mmap\_offset* field will contain an offset that can be passed to the [**mmap(2)**](/man/os/liburing/mmap.2) system call to map the region into the user space.

The *id* field is reserved and must be set to zero.

The *\_\_resv* fields must be filled with zeroes.

Available since kernel 6.13.

# [RETURN VALUE](#RETURN_VALUE)

On success [**io\_uring\_register\_region**(3)](/man/os/liburing/io_uring_register_region.3) returns 0. On failure it returns **-errno**.

January 13, 2026 liburing-2.14

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Document: io_uring_register_region(3) from liburing 2.15-r4 (Chainguard OS)
Source: https://github.com/axboe/liburing.git