ibv_alloc_user_buf, ibv_free_user_buf - associate an ibv_buf with application-owned memory
#include <infiniband/verbs.h> struct ibv_buf *ibv_alloc_user_buf(struct ibv_pd *pd, void *addr, size_t size, int dmabuf_fd); void ibv_free_user_buf(struct ibv_buf *buf);
ibv_alloc_user_buf() associates an ibv_buf with memory the application already owns, either a plain virtual address range or a DMA-buf. Unlike ibv_alloc_buf(), no memory is allocated; addr must already be a valid virtual address for that memory, and must remain valid for as long as the returned handle is in use.
ibv_free_user_buf() releases a handle returned by ibv_alloc_user_buf(). It does not free or otherwise affect the underlying memory; only the handle itself and any bookkeeping ibv_alloc_user_buf() performed (such as fork protection) are released.
The returned handle is meant for providers that accept an ibv_buf directly without registering an MR, such as driver-specific control-buffer descriptors.
Use of this API is discouraged. Applications should allocate buffers with ibv_alloc_buf() whenever possible. See NOTES below.
pd : Protection domain the buffer is associated with.
addr : Application-owned virtual address of the buffer.
size : Size of the buffer in bytes.
dmabuf_fd : A DMA-buf file descriptor backing the buffer, or -1 if the buffer is plain virtual memory at addr.
buf : Handle returned by ibv_alloc_user_buf(), to be released with ibv_free_user_buf().
ibv_alloc_buf() is the preferred way to obtain an ibv_buf. Its allocation is selected by the provider for the protection domain, and therefore accounts for platform requirements such as confidential computing (CoCo), where memory may have to be allocated as unprotected/shared memory (see IBV_PARENT_DOMAIN_INIT_ATTR_ALLOW_CC_UNPROTECTED_ALLOC in ibv_alloc_parent_domain(3)).
ibv_alloc_user_buf() bypasses this allocator abstraction. Neither libibverbs nor the provider can verify or adjust memory the application allocated itself, so the application is solely responsible for ensuring that the memory is suitable for the device and for the platform it runs on (for example, that it is usable by the device inside a CoCo guest). The application generally does not have enough information to guarantee this in a portable way.
Use this API only when the memory must come from a source that ibv_alloc_buf() cannot provide, such as an existing DMA-buf allocation shared with another device or subsystem, or memory whose lifetime is managed by the application. Otherwise, use ibv_alloc_buf().
ibv_alloc_user_buf() returns a buffer handle on success, or NULL if the request fails.
ibv_free_user_buf() does not return a value.
ibv_alloc_buf(3), ibv_alloc_parent_domain(3)