.TH "fi_direct" "7" "2017\-04\-13" "Libfabric Programmer\[aq]s Manual" "\@VERSION\@"
.SH NAME
.PP
Direct fabric provider access
.SH SYNOPSIS
.IP
.nf
\f[C]
\-DFABRIC_DIRECT

#define\ FABRIC_DIRECT
\f[]
.fi
.PP
Fabric direct provides a mechanism for applications to compile against a
specific fabric providers without going through the libfabric framework
or function vector tables.
This allows for extreme optimization via function inlining at the cost
of supporting multiple providers or different versions of the same
provider.
.SH DESCRIPTION
.PP
The use of fabric direct is intended only for applications that require
the absolute minimum software latency, and are willing to re\-compile
for specific fabric hardware.
Providers that support fabric direct implement their own versions of the
static inline calls which are define in the libfabric header files,
define selected enum values, and provide defines for compile\-time
optimizations.
Applications can then code against the standard libfabric calls, but
link directly against the provider calls by defining FABRIC_DIRECT as
part of their build.
.PP
In general, the use of fabric direct does not require application source
code changes, and, instead, is limited to the build process.
.PP
Providers supporting fabric direct must install \[aq]direct\[aq]
versions of all libfabric header files.
For convenience, the libfabric sources contain sample header files that
may be modified by a provider.
The \[aq]direct\[aq] header file names have \[aq]fi_direct\[aq] as their
prefix: fi_direct.h, fi_direct_endpoint.h, etc.
.PP
Direct providers are prohibited from overriding or modifying existing
data structures.
However, provider specific extensions are still available.
In addition to provider direct function calls to provider code, a fabric
direct provider may define zero of more of the following capability
definitions.
Applications can check for these capabilities in order to optimize code
paths at compile time, versus relying on run\-time checks.
.SH CAPABILITY DEFINITIONS
.PP
In order that application code may be optimized during compile time,
direct providers must provide definitions for various capabilities and
modes, if those capabilities are supported.
The following #define values may be used by an application to test for
provider support of supported features.
.PP
\f[I]FI_DIRECT_CONTEXT\f[] : The provider sets FI_CONTEXT or FI_CONTEXT2
for fi_info:mode.
See fi_getinfo for additional details.
When FI_DIRECT_CONTEXT is defined, applications should use struct
fi_context in their definitions, even if FI_CONTEXT2 is set.
.PP
\f[I]FI_DIRECT_LOCAL_MR\f[] : The provider sets FI_LOCAL_MR for
fi_info:mode.
See fi_getinfo for additional details.
.SH SEE ALSO
.PP
\f[C]fi_getinfo\f[](3), \f[C]fi_endpoint\f[](3), \f[C]fi_domain\f[](3)
.SH AUTHORS
OpenFabrics.