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 associ-
ated 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 trans-
fers, 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)
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