devlink: implement DEVLINK_CMD_REGION_NEW

Implement support for the DEVLINK_CMD_REGION_NEW command for creating
snapshots. This new command parallels the existing
DEVLINK_CMD_REGION_DEL.

In order for DEVLINK_CMD_REGION_NEW to work for a region, the new
".snapshot" operation must be implemented in the region's ops structure.

The desired snapshot id must be provided. This helps avoid confusion on
the purpose of DEVLINK_CMD_REGION_NEW, and keeps the API simpler.

The requested id will be inserted into the xarray tracking the number of
snapshots using each id. If this id is already used by another snapshot
on any region, an error will be returned.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/devlink/devlink-region.rst

@@ -20,6 +20,11 @@ address regions that are otherwise inaccessible to the user.
 Regions may also be used to provide an additional way to debug complex error
 states, but see also :doc:`devlink-health`
 
+Regions may optionally support capturing a snapshot on demand via the
+``DEVLINK_CMD_REGION_NEW`` netlink message. A driver wishing to allow
+requested snapshots must implement the ``.snapshot`` callback for the region
+in its ``devlink_region_ops`` structure.
+
 example usage
 -------------
 
@@ -40,6 +45,9 @@ example usage
     # Delete a snapshot using:
     $ devlink region del pci/0000:00:05.0/cr-space snapshot 1
 
+    # Request an immediate snapshot, if supported by the region
+    $ devlink region new pci/0000:00:05.0/cr-space snapshot 5
+
     # Dump a snapshot:
     $ devlink region dump pci/0000:00:05.0/fw-health snapshot 1
     0000000000000000 0014 95dc 0014 9514 0035 1670 0034 db30