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

include/net/devlink.h

@@ -501,10 +501,16 @@ struct devlink_info_req;
  * struct devlink_region_ops - Region operations
  * @name: region name
  * @destructor: callback used to free snapshot memory when deleting
+ * @snapshot: callback to request an immediate snapshot. On success,
+ *            the data variable must be updated to point to the snapshot data.
+ *            The function will be called while the devlink instance lock is
+ *            held.
  */
 struct devlink_region_ops {
 	const char *name;
 	void (*destructor)(const void *data);
+	int (*snapshot)(struct devlink *devlink, struct netlink_ext_ack *extack,
+			u8 **data);
 };
 
 struct devlink_fmsg;

net/core/devlink.c

@@ -3845,6 +3845,33 @@ static void __devlink_snapshot_id_decrement(struct devlink *devlink, u32 id)
 	}
 }
 
+/**
+ *	__devlink_snapshot_id_insert - Insert a specific snapshot ID
+ *	@devlink: devlink instance
+ *	@id: the snapshot id
+ *
+ *	Mark the given snapshot id as used by inserting a zero value into the
+ *	snapshot xarray.
+ *
+ *	This must be called while holding the devlink instance lock. Unlike
+ *	devlink_snapshot_id_get, the initial reference count is zero, not one.
+ *	It is expected that the id will immediately be used before
+ *	releasing the devlink instance lock.
+ *
+ *	Returns zero on success, or an error code if the snapshot id could not
+ *	be inserted.
+ */
+static int __devlink_snapshot_id_insert(struct devlink *devlink, u32 id)
+{
+	lockdep_assert_held(&devlink->lock);
+
+	if (WARN_ON(xa_load(&devlink->snapshot_ids, id)))
+		return -EEXIST;
+
+	return xa_err(xa_store(&devlink->snapshot_ids, id, xa_mk_value(0),
+			       GFP_KERNEL));
+}
+
 /**
  *	__devlink_region_snapshot_id_get - get snapshot ID
  *	@devlink: devlink instance
@@ -4038,6 +4065,71 @@ static int devlink_nl_cmd_region_del(struct sk_buff *skb,
 	return 0;
 }
 
+static int
+devlink_nl_cmd_region_new(struct sk_buff *skb, struct genl_info *info)
+{
+	struct devlink *devlink = info->user_ptr[0];
+	struct devlink_region *region;
+	const char *region_name;
+	u32 snapshot_id;
+	u8 *data;
+	int err;
+
+	if (!info->attrs[DEVLINK_ATTR_REGION_NAME]) {
+		NL_SET_ERR_MSG_MOD(info->extack, "No region name provided");
+		return -EINVAL;
+	}
+
+	if (!info->attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID]) {
+		NL_SET_ERR_MSG_MOD(info->extack, "No snapshot id provided");
+		return -EINVAL;
+	}
+
+	region_name = nla_data(info->attrs[DEVLINK_ATTR_REGION_NAME]);
+	region = devlink_region_get_by_name(devlink, region_name);
+	if (!region) {
+		NL_SET_ERR_MSG_MOD(info->extack, "The requested region does not exist");
+		return -EINVAL;
+	}
+
+	if (!region->ops->snapshot) {
+		NL_SET_ERR_MSG_MOD(info->extack, "The requested region does not support taking an immediate snapshot");
+		return -EOPNOTSUPP;
+	}
+
+	if (region->cur_snapshots == region->max_snapshots) {
+		NL_SET_ERR_MSG_MOD(info->extack, "The region has reached the maximum number of stored snapshots");
+		return -ENOSPC;
+	}
+
+	snapshot_id = nla_get_u32(info->attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID]);
+
+	if (devlink_region_snapshot_get_by_id(region, snapshot_id)) {
+		NL_SET_ERR_MSG_MOD(info->extack, "The requested snapshot id is already in use");
+		return -EEXIST;
+	}
+
+	err = __devlink_snapshot_id_insert(devlink, snapshot_id);
+	if (err)
+		return err;
+
+	err = region->ops->snapshot(devlink, info->extack, &data);
+	if (err)
+		goto err_snapshot_capture;
+
+	err = __devlink_region_snapshot_create(region, data, snapshot_id);
+	if (err)
+		goto err_snapshot_create;
+
+	return 0;
+
+err_snapshot_create:
+	region->ops->destructor(data);
+err_snapshot_capture:
+	__devlink_snapshot_id_decrement(devlink, snapshot_id);
+	return err;
+}
+
 static int devlink_nl_cmd_region_read_chunk_fill(struct sk_buff *msg,
 						 struct devlink *devlink,
 						 u8 *chunk, u32 chunk_size,
@@ -6446,6 +6538,13 @@ static const struct genl_ops devlink_nl_ops[] = {
 		.flags = GENL_ADMIN_PERM,
 		.internal_flags = DEVLINK_NL_FLAG_NEED_DEVLINK,
 	},
+	{
+		.cmd = DEVLINK_CMD_REGION_NEW,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit = devlink_nl_cmd_region_new,
+		.flags = GENL_ADMIN_PERM,
+		.internal_flags = DEVLINK_NL_FLAG_NEED_DEVLINK,
+	},
 	{
 		.cmd = DEVLINK_CMD_REGION_DEL,
 		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,