--- name: "ibv_alloc_mw" section: "3" platform: "linux" package: "rdma-core" version: "65.0-1" release: "Arch Linux 2026-11-01" platforms: ["linux", "freebsd"] url: "https://new.carta.tech/ibv_alloc_mw" --- # ibv\_alloc\_mw(3) allocate or deallocate a memory window (MW) ## NAME ibv\_alloc\_mw, ibv\_dealloc\_mw - allocate or deallocate a memory window (MW) ## SYNOPSIS ``` #include struct ibv_mw *ibv_alloc_mw(struct ibv_pd *pd, enum ibv_mw_type type); int ibv_dealloc_mw(struct ibv_mw *mw); ``` ## DESCRIPTION **ibv\_alloc\_mw()** allocates a memory window (MW) associated with the protection domain *pd.* The MW's type (1 or 2A/2B) is *type.* The MW is created not bound. For it to be useful, the MW must be bound, through either ibv\_bind\_mw (type 1) or a special WR (type 2). Once bound, the memory window allows RDMA (remote) access to a subset of the MR to which it was bound, until invalidated by: ibv\_bind\_mw verb with zero length for type 1, IBV\_WR\_LOCAL\_INV/IBV\_WR\_SEND\_WITH\_INV WR opcode for type 2, deallocation. **ibv\_dealloc\_mw()** Unbinds in case was previously bound and deallocates the MW *mw.* ## RETURN VALUE **ibv\_alloc\_mw()** returns a pointer to the allocated MW, or NULL if the request fails. The remote key (**R\_Key**) field **rkey** is used by remote processes to perform Atomic and RDMA operations. This key will be changed during bind operations. The remote process places this **rkey** as the rkey field of struct ibv\_send\_wr passed to the ibv\_post\_send function. **ibv\_dealloc\_mw()** 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\_bind\_mw**(3)](/ibv_bind_mw/3.md), [**ibv\_reg\_mr**(3)](/ibv_reg_mr/3.md), ## AUTHORS - Majd Dibbiny \ - Yishai Hadas \