verbs: Introduce ibv_dm_export_dmabuf_fd() verb

This API exports a dmabuf fd that is associated with a given ibv_dm.

Upon success the returned fd can be used for DMA and RDMA operations
associated with it.

Once the usage has been ended, close() should be called while supplying
the fd. This call will release the resources that were earlier allocated
using the ibv_dm_export_dmabuf_fd() API.

A detailed man page was added as well.

Signed-off-by: Yishai Hadas <yishaih@nvidia.com>

Author: yishaih

debian/libibverbs1.symbols

@@ -58,6 +58,7 @@ libibverbs.so.1 libibverbs1 #MINVER#
  ibv_destroy_srq@IBVERBS_1.1 1.1.6
  ibv_detach_mcast@IBVERBS_1.0 1.1.6
  ibv_detach_mcast@IBVERBS_1.1 1.1.6
+ ibv_dm_export_dmabuf_fd@IBVERBS_1.16 62
  ibv_dofork_range@IBVERBS_1.1 1.1.6
  ibv_dontfork_range@IBVERBS_1.1 1.1.6
  ibv_event_type_str@IBVERBS_1.1 1.1.6

libibverbs/driver.h

@@ -407,6 +407,7 @@ struct verbs_context_ops {
 	int (*destroy_wq)(struct ibv_wq *wq);
 	int (*detach_mcast)(struct ibv_qp *qp, const union ibv_gid *gid,
 			    uint16_t lid);
+	int (*dm_export_dmabuf_fd)(struct ibv_dm *dm);
 	void (*free_context)(struct ibv_context *context);
 	int (*free_dm)(struct ibv_dm *dm);
 	int (*get_srq_num)(struct ibv_srq *srq, uint32_t *srq_num);

libibverbs/dummy_ops.c

@@ -285,6 +285,12 @@ static int detach_mcast(struct ibv_qp *qp, const union ibv_gid *gid,
 	return EOPNOTSUPP;
 }
 
+static int dm_export_dmabuf_fd(struct ibv_dm *dm)
+{
+	errno = EOPNOTSUPP;
+	return -1;
+}
+
 static void free_context(struct ibv_context *ctx)
 {
 	return;
@@ -569,6 +575,7 @@ const struct verbs_context_ops verbs_dummy_ops = {
 	destroy_srq,
 	destroy_wq,
 	detach_mcast,
+	dm_export_dmabuf_fd,
 	free_context,
 	free_dm,
 	get_srq_num,
@@ -698,6 +705,7 @@ void verbs_set_ops(struct verbs_context *vctx,
 	SET_PRIV_OP(ctx, destroy_srq);
 	SET_OP(vctx, destroy_wq);
 	SET_PRIV_OP(ctx, detach_mcast);
+	SET_OP(vctx, dm_export_dmabuf_fd);
 	SET_PRIV_OP_IC(ctx, free_context);
 	SET_OP(vctx, free_dm);
 	SET_OP(vctx, get_srq_num);

libibverbs/libibverbs.map.in

@@ -173,6 +173,7 @@ IBVERBS_1.15 {
 
 IBVERBS_1.16 {
 	global:
+		ibv_dm_export_dmabuf_fd;
 		ibv_query_port_speed;
 } IBVERBS_1.15;
 

libibverbs/man/CMakeLists.txt

@@ -28,6 +28,7 @@ rdma_man_pages(
   ibv_create_wq.3
   ibv_devices.1
   ibv_devinfo.1
+  ibv_dm_export_dmabuf_fd.3.md
   ibv_event_type_str.3.md
   ibv_fork_init.3.md
   ibv_get_async_event.3

libibverbs/man/ibv_dm_export_dmabuf_fd.3.md

@@ -0,0 +1,49 @@
+---
+date: 2025-12-7
+footer: libibverbs
+header: "Libibverbs Programmer's Manual"
+layout: page
+license: 'Licensed under the OpenIB.org BSD license (FreeBSD Variant) - See COPYING.md'
+section: 3
+title: ibv_dm_export_dmabuf_fd
+---
+
+# NAME
+
+ibv_dm_export_dmabuf_fd - export dmabuf fd for a given ibv_dm.
+
+# SYNOPSIS
+
+```c
+#include <infiniband/verbs.h>
+
+int ibv_dm_export_dmabuf_fd(struct ibv_dm *dm);
+```
+
+# DESCRIPTION
+
+**ibv_dm_export_dmabuf_fd()** exports a dmabuf fd that is associated with the given
+*dm*.
+
+The returned fd can be later used for DMA and RDMA operations associated with it.
+
+Once the usage has been ended close() should be called while supplying the fd.
+
+This call will release resources that were earlier allocated using the **ibv_dm_export_dmabuf_fd()** API.
+
+# ARGUMENTS
+
+*dm*
+:	An ibv_dm pointer to export the dmabuf fd for its memory.
+
+# RETURN VALUE
+
+**ibv_dm_export_dmabuf_fd()** returns an fd number >= 0 upon success, or -1 if the request fails and errno set to the error.
+
+# SEE ALSO
+
+**ibv_reg_mr_ex**(3)
+
+# AUTHOR
+
+Yishai Hadas <yishaih@nvidia.com>

libibverbs/verbs.c

@@ -412,6 +412,11 @@ int ibv_dealloc_dmah(struct ibv_dmah *dmah)
 	return get_ops(dmah->context)->dealloc_dmah(dmah);
 }
 
+int ibv_dm_export_dmabuf_fd(struct ibv_dm *dm)
+{
+	return get_ops(dm->context)->dm_export_dmabuf_fd(dm);
+}
+
 struct ibv_mr *ibv_reg_dmabuf_mr(struct ibv_pd *pd, uint64_t offset,
 				 size_t length, uint64_t iova, int fd,
 				 int access)

libibverbs/verbs.h

@@ -2183,6 +2183,7 @@ struct ibv_values_ex {
 
 struct verbs_context {
 	/*  "grows up" - new fields go here */
+	int (*dm_export_dmabuf_fd)(struct ibv_dm *dm);
 	struct ibv_mr *(*reg_mr_ex)(struct ibv_pd *pd,
 				    struct ibv_mr_init_attr *mr_init_attr);
 	int (*dealloc_dmah)(struct ibv_dmah *dmah);
@@ -2837,6 +2838,8 @@ int ibv_free_dm(struct ibv_dm *dm)
 	return vctx->free_dm(dm);
 }
 
+int ibv_dm_export_dmabuf_fd(struct ibv_dm *dm);
+
 /**
  * ibv_memcpy_to/from_dm - copy to/from device allocated memory
  * @dm - The DM to copy to/from