---
name: "ibv_reg_mr"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/ibv_reg_mr"
---

# ibv\_reg\_mr(3)

register or deregister a memory region (MR)

## NAME

ibv\_reg\_mr, ibv\_dereg\_mr - register or deregister a memory region (MR)

## SYNOPSIS

```
#include <infiniband/verbs.h>

struct ibv_mr *ibv_reg_mr(struct ibv_pd *pd, void *addr,
                          size_t length, int access);

int ibv_dereg_mr(struct ibv_mr *mr);
```

## DESCRIPTION

**ibv\_reg\_mr()** registers a memory region (MR) associated with the protection domain *pd.* The MR's starting address is *addr* and its size is *length.* The argument *access* describes the desired memory protection attributes; it is either 0 or the bitwise OR of one or more of the following flags:

- **IBV\_ACCESS\_LOCAL\_WRITE Enable Local Write Access**

  - **IBV\_ACCESS\_REMOTE\_WRITE Enable Remote Write Access**

  - **IBV\_ACCESS\_REMOTE\_READ Enable Remote Read Access**

  - **IBV\_ACCESS\_REMOTE\_ATOMIC Enable Remote Atomic Operation Access (if supported)**

  - **IBV\_ACCESS\_MW\_BIND Enable Memory Window Binding**

  - **IBV\_ACCESS\_ON\_DEMAND Create an on-demand paging MR**

  If **IBV\_ACCESS\_REMOTE\_WRITE** or **IBV\_ACCESS\_REMOTE\_ATOMIC** is set, then **IBV\_ACCESS\_LOCAL\_WRITE** must be set too.

Local read access is always enabled for the MR.

**ibv\_dereg\_mr()** deregisters the MR *mr.*

## RETURN VALUE

**ibv\_reg\_mr()** returns a pointer to the registered MR, or NULL if the request fails. The local key (**L\_Key**) field **lkey** is used as the lkey field of struct ibv\_sge when posting buffers with ibv\_post\_\* verbs, and the the remote key (**R\_Key**) field **rkey** is used by remote processes to perform Atomic and RDMA operations.  The remote process places this **rkey** as the rkey field of struct ibv\_send\_wr passed to the ibv\_post\_send function.

**ibv\_dereg\_mr()** returns 0 on success, or the value of errno on failure (which indicates the failure reason).

## NOTES

**ibv\_dereg\_mr()** fails if any memory window is still bound to this MR.

## SEE ALSO

[**ibv\_alloc\_pd**(3)](/ibv_alloc_pd/3.md), [**ibv\_post\_send**(3)](/ibv_post_send/3.md), [**ibv\_post\_recv**(3)](/ibv_post_recv/3.md), [**ibv\_post\_srq\_recv**(3)](/ibv_post_srq_recv/3.md)

## AUTHORS

- Dotan Barak \<dotanba@gmail.com\>