devlink: Add Documentation/networking/devlink-health.txt

The health mechanism is targeted for Real Time Alerting, in order to know when

something bad had happened to a PCI device

- Provide alert debug information

- Self healing

- If problem needs vendor support, provide a way to gather all needed debugging

  information.

The main idea is to unify and centralize driver health reports in the

generic devlink instance and allow the user to set different

attributes of the health reporting and recovery procedures.

The devlink health reporter:

Device driver creates a "health reporter" per each error/health type.

Error/Health type can be a known/generic (eg pci error, fw error, rx/tx error)

or unknown (driver specific).

For each registered health reporter a driver can issue error/health reports

asynchronously. All health reports handling is done by devlink.

Device driver can provide specific callbacks for each "health reporter", e.g.

 - Recovery procedures

 - Diagnostics and object dump procedures

 - OOB initial parameters

Different parts of the driver can register different types of health reporters

with different handlers.

Once an error is reported, devlink health will do the following actions:

  * A log is being send to the kernel trace events buffer

  * Health status and statistics are being updated for the reporter instance

  * Object dump is being taken and saved at the reporter instance (as long as

    there is no other dump which is already stored)

  * Auto recovery attempt is being done. Depends on:

    - Auto-recovery configuration

    - Grace period vs. time passed since last recover

The user interface:

User can access/change each reporter's parameters and driver specific callbacks

via devlink, e.g per error type (per health reporter)

 - Configure reporter's generic parameters (like: disable/enable auto recovery)

 - Invoke recovery procedure

 - Run diagnostics

 - Object dump

The devlink health interface (via netlink):

DEVLINK_CMD_HEALTH_REPORTER_GET

  Retrieves status and configuration info per DEV and reporter.

DEVLINK_CMD_HEALTH_REPORTER_SET

  Allows reporter-related configuration setting.

DEVLINK_CMD_HEALTH_REPORTER_RECOVER

  Triggers a reporter's recovery procedure.

DEVLINK_CMD_HEALTH_REPORTER_DIAGNOSE

  Retrieves diagnostics data from a reporter on a device.

DEVLINK_CMD_HEALTH_REPORTER_DUMP_GET

  Retrieves the last stored dump. Devlink health

  saves a single dump. If an dump is not already stored by the devlink

  for this reporter, devlink generates a new dump.

  dump output is defined by the reporter.

DEVLINK_CMD_HEALTH_REPORTER_DUMP_CLEAR

  Clears the last saved dump file for the specified reporter.

                                               netlink

                                      +--------------------------+

                                      |                          |

                                      |            +             |

                                      |            |             |

                                      +--------------------------+

                                                   |request for ops

                                                   |(diagnose,

 mlx5_core                             devlink     |recover,

                                                   |dump)

+--------+                            +--------------------------+

|        |                            |    reporter|             |

|        |                            |  +---------v----------+  |

|        |   ops execution            |  |                    |  |

|     <----------------------------------+                    |  |

|        |                            |  |                    |  |

|        |                            |  + ^------------------+  |

|        |                            |    | request for ops     |

|        |                            |    | (recover, dump)     |

|        |                            |    |                     |

|        |                            |  +-+------------------+  |

|        |     health report          |  | health handler     |  |

|        +------------------------------->                    |  |

|        |                            |  +--------------------+  |

|        |     health reporter create |                          |

|        +---------------------------->                          |

+--------+                            +--------------------------+