devlink: track snapshot id usage count using an xarray
Each snapshot created for a devlink region must have an id. These ids are supposed to be unique per "event" that caused the snapshot to be created. Drivers call devlink_region_snapshot_id_get to obtain a new id to use for a new event trigger. The id values are tracked per devlink, so that the same id number can be used if a triggering event creates multiple snapshots on different regions. There is no mechanism for snapshot ids to ever be reused. Introduce an xarray to store the count of how many snapshots are using a given id, replacing the snapshot_id field previously used for picking the next id. The devlink_region_snapshot_id_get() function will use xa_alloc to insert an initial value of 1 value at an available slot between 0 and U32_MAX. The new __devlink_snapshot_id_increment() and __devlink_snapshot_id_decrement() functions will be used to track how many snapshots currently use an id. Drivers must now call devlink_snapshot_id_put() in order to release their reference of the snapshot id after adding region snapshots. By tracking the total number of snapshots using a given id, it is possible for the decrement() function to erase the id from the xarray when it is not in use. With this method, a snapshot id can become reused again once all snapshots that referred to it have been deleted via DEVLINK_CMD_REGION_DEL, and the driver has finished adding snapshots. This work also paves the way to introduce a mechanism for userspace to request a snapshot. 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>
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