devlink: let kernel allocate region snapshot id

Currently users have to choose a free snapshot id before
calling DEVLINK_CMD_REGION_NEW. This is potentially racy
and inconvenient.

Make the DEVLINK_ATTR_REGION_SNAPSHOT_ID optional and try
to allocate id automatically. Send a message back to the
caller with the snapshot info.

Example use:
$ devlink region new netdevsim/netdevsim1/dummy
netdevsim/netdevsim1/dummy: snapshot 1

$ id=$(devlink -j region new netdevsim/netdevsim1/dummy | \
       jq '.[][][][]')
$ devlink region dump netdevsim/netdevsim1/dummy snapshot $id
[...]
$ devlink region del netdevsim/netdevsim1/dummy snapshot $id

v4:
 - inline the notification code
v3:
 - send the notification only once snapshot creation completed.
v2:
 - don't wrap the line containing extack;
 - add a few sentences to the docs.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/tools/testing/selftests/drivers/net/netdevsim/devlink.sh b/tools/testing/selftests/drivers/net/netdevsim/devlink.sh
index 9f9741444549..ad539eccddcb 100755
--- a/tools/testing/selftests/drivers/net/netdevsim/devlink.sh
+++ b/tools/testing/selftests/drivers/net/netdevsim/devlink.sh
@@ -151,6 +151,19 @@ regions_test()
 
 	check_region_snapshot_count dummy post-second-delete 2
 
+	sid=$(devlink -j region new $DL_HANDLE/dummy | jq '.[][][][]')
+	check_err $? "Failed to create a new snapshot with id allocated by the kernel"
+
+	check_region_snapshot_count dummy post-first-request 3
+
+	devlink region dump $DL_HANDLE/dummy snapshot $sid >> /dev/null
+	check_err $? "Failed to dump a snapshot with id allocated by the kernel"
+
+	devlink region del $DL_HANDLE/dummy snapshot $sid
+	check_err $? "Failed to delete snapshot with id allocated by the kernel"
+
+	check_region_snapshot_count dummy post-first-request 2
+
 	log_test "regions test"
 }