Re: [PATCH 08/10] devlink: implement DEVLINK_CMD_REGION_NEW

[Jiri Pirko <jiri@resnulli.us>]

Tue, Mar 24, 2020 at 11:34:43PM CET, jacob.e.keller@intel.com wrote:
>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>
>---
> .../networking/devlink/devlink-region.rst     |   8 ++
> include/net/devlink.h                         |   6 +
> net/core/devlink.c                            | 103 ++++++++++++++++++
> 3 files changed, 117 insertions(+)
>
>diff --git a/Documentation/networking/devlink/devlink-region.rst b/Documentation/networking/devlink/devlink-region.rst
>index 8b46e8591fe0..9d2d4c95a5c4 100644
>--- a/Documentation/networking/devlink/devlink-region.rst
>+++ b/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
>diff --git a/include/net/devlink.h b/include/net/devlink.h
>index 30306e62fe73..ae894e073050 100644
>--- a/include/net/devlink.h
>+++ b/include/net/devlink.h
>@@ -502,10 +502,16 @@ 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;
>diff --git a/net/core/devlink.c b/net/core/devlink.c
>index b3698228a6ed..16129ec27913 100644
>--- a/net/core/devlink.c
>+++ b/net/core/devlink.c
>@@ -3849,6 +3849,35 @@ 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.
>+ *
>+ *	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)
>+{
>+	int err;
>+
>+	lockdep_assert_held(&devlink->lock);
>+
>+	/* Check to make sure it's empty first */
>+	if (xa_load(&devlink->snapshot_ids, id))

How this can happen? The entry was just allocated. WARN_ON.


>+		return -EBUSY;
>+
>+	err = xa_err(xa_store(&devlink->snapshot_ids, id, xa_mk_value(0),
>+			      GFP_KERNEL));

Just return and avoid err variable.


>+	if (err)
>+		return err;
>+
>+	return 0;
>+}
>+
> /**
>  *	__devlink_region_snapshot_id_get - get snapshot ID
>  *	@devlink: devlink instance
>@@ -4048,6 +4077,73 @@ 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 -ENOMEM;

Maybe ENOBUFS or ENOSPC? ENOMEM seems odd as it is related to memory
allocation fails which this is not.


>+	}
>+
>+	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) {
>+		NL_SET_ERR_MSG_MOD(info->extack, "The requested snapshot id is already in used");

Different message would be appropriate.


>+		return err;
>+	}
>+
>+	err = region->ops->snapshot(devlink, info->extack, &data);
>+	if (err)
>+		goto err_decrement_snapshot_count;
>+
>+	err = __devlink_region_snapshot_create(region, data, snapshot_id);
>+	if (err)
>+		goto err_free_snapshot_data;
>+
>+	return 0;
>+
>+err_decrement_snapshot_count:
>+	__devlink_snapshot_id_decrement(devlink, snapshot_id);
>+err_free_snapshot_data:

In devlink the error labers are named according to actions that failed.
Please align.


>+	region->ops->destructor(data);
>+	return err;
>+}
>+
> static int devlink_nl_cmd_region_read_chunk_fill(struct sk_buff *msg,
> 						 struct devlink *devlink,
> 						 u8 *chunk, u32 chunk_size,
>@@ -6455,6 +6551,13 @@ 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,
>-- 
>2.24.1
>