netdev - Re: [PATCH net-next v3 08/11] devlink: track snapshot id usage count using an xarray

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Message-ID: <20200326211653.GE11304@nanopsycho.orion>
Date:   Thu, 26 Mar 2020 22:16:53 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jacob Keller <jacob.e.keller@...el.com>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next v3 08/11] devlink: track snapshot id usage count
 using an xarray

Thu, Mar 26, 2020 at 07:37:15PM CET, jacob.e.keller@...el.com wrote:
>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@...el.com>

Reviewed-by: Jiri Pirko <jiri@...lanox.com>