NAME

       ibv_alloc_dm, ibv_free_dm, ibv_memcpy_to/from_dm - allocate or free a device memory buffer
       (DMs) and perform memory copy to or from it

SYNOPSIS

       #include <infiniband/verbs.h>

       struct ibv_dm *ibv_alloc_dm(struct ibv_context *context,
                                   struct ibv_alloc_dm_attr *attr);

       int ibv_free_dm(struct ibv_dm *dm);

DESCRIPTION

       ibv_alloc_dm() allocates a device memory buffer for the RDMA device context context.   The
       argument   attr   is   a   pointer   to   an   ibv_alloc_dm_attr  struct,  as  defined  in
       <infiniband/verbs.h>.

       ibv_free_dm() free the device memory buffer dm.

       struct ibv_alloc_dm_attr {
               size_t length;           /* Length of desired device memory buffer */
               uint32_t log_align_req;       /* Log base 2 of address alignment requirement */
               uint32_t comp_mask;      /* Compatibility mask that defines which of the following variables are valid */
       };

       Address alignment may be required in cases where RDMA atomic operations will be performed using the device memory.

       In such cases, the user may specify the device memory start address alignment using the log_align_req parameter

       in the allocation attributes struct.

Accessing an allocated device memory

       In order to perform a write/read memory access to an allocated device memory, a user could use the ibv_memcpy_to_dm
       and ibv_memcpy_from_dm calls respectively.

       int ibv_memcpy_to_dm(struct ibv_dm *dm, uint64_t dm_offset,
                            void *host_addr, size_t length);

       int ibv_memcpy_from_dm(void *host_addr, struct ibv_dm *dm,
                          uint64_t dm_offset, size_t length);

       dm_offest
       is the byte offset from the beginning of the allocated device memory buffer to access.

       host_addr
       is the host memory buffer address to access.

       length
       is the copy length in bytes.

Device memory registration

       User may register the allocated device memory as a memory region and use the lkey/rkey inside sge when posting receive
       or sending work request. This type of MR is defined as zero based and therefore any reference to it (specifically in sge)
       is done with a byte offset from the beginning of the region.

       This type of registration is done using ibv_reg_dm_mr.

       struct ibv_mr* ibv_reg_dm_mr(struct ibv_pd *pd, struct ibv_dm *dm, uint64_t dm_offset,
                         size_t length, uint32_t access);

       pd
       the associated pd for this registration.

       dm
       the associated dm for this registartion.

       dm_offest
       is the byte offset from the beginning of the allocated device memory buffer to register.

       length
       the memory length to register.

       access
       mr access flags (Use enum ibv_access_flags). For this type of registration, user must set the IBV_ACCESS_ZERO_BASED
       flag.

RETURN VALUE

       ibv_alloc_dm() returns a pointer to an ibv_dm struct or NULL if the  request  fails.   The
       output dm contains the handle which could be used by user to import this device memory.

       ibv_free_dm()  returns 0 on success, or the value of errno on failure (which indicates the
       failure reason).

       ibv_reg_dm_mr() returns a pointer to an ibv_mr struct on success or NULL if request fails.

       ibv_memcpy_to_dm()/ibv_memcpy_from_dm() returns 0 on success or the failure  reason  value
       on failure.

NOTES

       ibv_alloc_dm()  may  fail if device has no more free device memory left, where the maximum
       amount of allocated memory is provided by the max_dm_size attribute in  ibv_device_attr_ex
       struct.  ibv_free_dm() may fail if any other resources (such as an MR) is still associated
       with the DM being freed.

SEE ALSO

       ibv_query_device_ex(3),

AUTHORS

       Ariel Levkovich <lariel@mellanox.com>