Changing the Source of Topology Discovery

## Enumerations

enum | hwloc_topology_components_flag_e { HWLOC_TOPOLOGY_COMPONENTS_FLAG_BLACKLIST }

## Functions

int | hwloc_topology_set_pid (hwloc_topology_t restrict topology, hwloc_pid_t pid)
int | hwloc_topology_set_synthetic (hwloc_topology_t restrict topology, const char *restrict description)
int | hwloc_topology_set_xml (hwloc_topology_t restrict topology, const char *restrict xmlpath)
int | hwloc_topology_set_xmlbuffer (hwloc_topology_t restrict topology, const char *restrict buffer, int size)
int | hwloc_topology_set_components (hwloc_topology_t restrict topology, unsigned long flags, const char *restrict name)

## Detailed Description

These functions must be called between hwloc_topology_init() and hwloc_topology_load(). Otherwise, they will return -1 with errno set to `EBUSY`.

If none of the functions below is called, the default is to detect all the objects of the machine that the caller is allowed to access.

This default behavior may also be modified through environment variables if the application did not modify it already. Setting HWLOC_XMLFILE in the environment enforces the discovery from a XML file as if hwloc_topology_set_xml() had been called. Setting HWLOC_SYNTHETIC enforces a synthetic topology as if hwloc_topology_set_synthetic() had been called.

Finally, HWLOC_THISSYSTEM enforces the return value of hwloc_topology_is_thissystem().

## Enumeration Type Documentation

## hwloc_topology_components_flag_e

enum hwloc_topology_components_flag_e

Flags to be passed to hwloc_topology_set_components()

Enumerator
HWLOC_TOPOLOGY_COMPONENTS_FLAG_BLACKLIST | Blacklist the target component from being used.

## Function Documentation

## hwloc_topology_set_components()

int hwloc_topology_set_components | ( | hwloc_topology_t restrict | topology,
|  | unsigned long | flags,
|  | const char *restrict | name
| ) |  |

Prevent a discovery component from being used for a topology.

`name` is the name of the discovery component that should not be used when loading topology `topology`. The name is a string such as "cuda".

For components with multiple phases, it may also be suffixed with the name of a phase, for instance "linux:io".

`flags` should be HWLOC_TOPOLOGY_COMPONENTS_FLAG_BLACKLIST.

This may be used to avoid expensive parts of the discovery process. For instance, CUDA-specific discovery may be expensive and unneeded while generic I/O discovery could still be useful.

Returns
  0 on success.
  -1 on error, for instance if flags are invalid.

## hwloc_topology_set_pid()

int hwloc_topology_set_pid | ( | hwloc_topology_t restrict | topology,
|  | hwloc_pid_t | pid
| ) |  |

Change which process the topology is viewed from.

On some systems, processes may have different views of the machine, for instance the set of allowed CPUs. By default, hwloc exposes the view from the current process. Calling hwloc_topology_set_pid() permits to make it expose the topology of the machine from the point of view of another process.

Note
  `hwloc_pid_t` is `pid_t` on Unix platforms, and `HANDLE` on native Windows platforms.
  -1 is returned and errno is set to `ENOSYS` on platforms that do not support this feature.
  The PID will not actually be used until hwloc_topology_load(). If the corresponding process exits in the meantime, hwloc will ignore the PID. If another process reuses the PID, the view of that process will be used.

Returns
  0 on success, -1 on error.

## hwloc_topology_set_synthetic()

int hwloc_topology_set_synthetic | ( | hwloc_topology_t restrict | topology,
|  | const char *restrict | description
| ) |  |

Enable synthetic topology.

Gather topology information from the given `description`, a space-separated string of <type:number> describing the object type and arity at each level. All types may be omitted (space-separated string of numbers) so that hwloc chooses all types according to usual topologies. See also the Synthetic topologies.

Setting the environment variable HWLOC_SYNTHETIC may also result in this behavior.

If `description` was properly parsed and describes a valid topology configuration, this function returns 0. Otherwise -1 is returned and errno is set to `EINVAL`.

Note that this function does not actually load topology information; it just tells hwloc where to load it from. You'll still need to invoke hwloc_topology_load() to actually load the topology information.

Returns
  0 on success.
  -1 with errno set to `EINVAL` if the description was invalid.

Note
  For convenience, this backend provides empty binding hooks which just return success.
  On success, the synthetic component replaces the previously enabled component (if any), but the topology is not actually modified until hwloc_topology_load().

## hwloc_topology_set_xml()

int hwloc_topology_set_xml | ( | hwloc_topology_t restrict | topology,
|  | const char *restrict | xmlpath
| ) |  |

Enable XML-file based topology.

Gather topology information from the XML file given at `xmlpath`. Setting the environment variable HWLOC_XMLFILE may also result in this behavior. This file may have been generated earlier with hwloc_topology_export_xml() in hwloc/export.h, or lstopo file.xml.

Note that this function does not actually load topology information; it just tells hwloc where to load it from. You'll still need to invoke hwloc_topology_load() to actually load the topology information.

Returns
  0 on success.
  -1 with errno set to `EINVAL` on failure to read the XML file.

Note
  See also hwloc_topology_set_userdata_import_callback() for importing application-specific object userdata.
  For convenience, this backend provides empty binding hooks which just return success. To have hwloc still actually call OS-specific hooks, the HWLOC_TOPOLOGY_FLAG_IS_THISSYSTEM has to be set to assert that the loaded file is really the underlying system.
  On success, the XML component replaces the previously enabled component (if any), but the topology is not actually modified until hwloc_topology_load().
  If an invalid XML input file is given, the error may be reported either here or later by hwloc_topology_load() depending on the XML library used by hwloc.

## hwloc_topology_set_xmlbuffer()

int hwloc_topology_set_xmlbuffer | ( | hwloc_topology_t restrict | topology,
|  | const char *restrict | buffer,
|  | int | size
| ) |  |

Enable XML based topology using a memory buffer (instead of a file, as with hwloc_topology_set_xml()).

Gather topology information from the XML memory buffer given at `buffer` and of length `size` (including an ending `\0`). This buffer may have been filled earlier with hwloc_topology_export_xmlbuffer() in hwloc/export.h.

Note that this function does not actually load topology information; it just tells hwloc where to load it from. You'll still need to invoke hwloc_topology_load() to actually load the topology information.

Returns
  0 on success.
  -1 with errno set to `EINVAL` on failure to read the XML buffer.

Note
  See also hwloc_topology_set_userdata_import_callback() for importing application-specific object userdata.
  For convenience, this backend provides empty binding hooks which just return success. To have hwloc still actually call OS-specific hooks, the HWLOC_TOPOLOGY_FLAG_IS_THISSYSTEM has to be set to assert that the loaded file is really the underlying system.
  On success, the XML component replaces the previously enabled component (if any), but the topology is not actually modified until hwloc_topology_load().
  If an invalid XML input file is given, the error may be reported either here or later by hwloc_topology_load() depending on the XML library used by hwloc.