ibv_alloc_null_mr(3)    Libibverbs Programmer's Manual    ibv_alloc_null_mr(3)

NAME
       ibv_alloc_null_mr - allocate a null memory region (MR)

SYNOPSIS
              #include <infiniband/verbs.h>

              struct ibv_mr *ibv_alloc_null_mr(struct ibv_pd *pd);

DESCRIPTION
       ibv_alloc_null_mr() allocates a null memory region (MR) that is
       associated with the protection domain pd.

       A null MR discards all data written to it, and always returns 0 on
       read.  It has the maximum length and only the lkey is valid, the MR is
       not exposed as an rkey.

       A device should implement the null MR in a way that bypasses PCI
       transfers, internally discarding or sourcing 0 data.  This provides a
       way to avoid PCI bus transfers by using a scatter/gather list in
       commands if applications do not intend to access the data, or need data
       to be 0 filled.

       Specifically upon ibv_post_send() the device skips PCI read cycles and
       upon ibv_post_recv() the device skips PCI write cycles which finally
       improves performance.

       ibv_dereg_mr() deregisters the MR.  The use of ibv_rereg_mr() or
       ibv_bind_mw() with this MR is invalid.

RETURN VALUE
       ibv_alloc_null_mr() returns a pointer to the allocated MR, or NULL if
       the request fails.

SEE ALSO
       ibv_reg_mr(3), ibv_dereg_mr(3),

AUTHOR
       Yonatan Cohen <yonatanc@mellanox.com>

libibverbs                         2018-6-1               ibv_alloc_null_mr(3)