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Date:   Wed, 29 Apr 2020 16:38:13 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net, jiri@...nulli.us
Cc:     netdev@...r.kernel.org, kernel-team@...com,
        jacob.e.keller@...el.com, Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net-next v2] 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.

The message carrying id gets sent immediately, but the
allocation is only valid if the entire operation succeeded.
This makes life easier, as sending the notification itself
may fail.

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

v2:
 - don't wrap the line containing extack;
 - add a few sentences to the docs.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
---
 .../networking/devlink/devlink-region.rst     | 10 ++-
 net/core/devlink.c                            | 83 ++++++++++++++++---
 .../drivers/net/netdevsim/devlink.sh          | 13 +++
 3 files changed, 91 insertions(+), 15 deletions(-)

diff --git a/Documentation/networking/devlink/devlink-region.rst b/Documentation/networking/devlink/devlink-region.rst
index 04e04d1ff627..b163d09a3d0d 100644
--- a/Documentation/networking/devlink/devlink-region.rst
+++ b/Documentation/networking/devlink/devlink-region.rst
@@ -23,7 +23,12 @@ 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.
+in its ``devlink_region_ops`` structure. If snapshot id is not set in
+the ``DEVLINK_CMD_REGION_NEW`` request kernel will allocate one and send
+the snapshot information to user space. Note that receiving the snapshot
+information does not guarantee that the snapshot creation completed
+successfully, user space must check the status of the operation before
+proceeding.
 
 example usage
 -------------
@@ -45,7 +50,8 @@ example usage
     $ 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
+    $ devlink region new pci/0000:00:05.0/cr-space
+    pci/0000:00:05.0/cr-space: snapshot 5
 
     # Dump a snapshot:
     $ devlink region dump pci/0000:00:05.0/fw-health snapshot 1
diff --git a/net/core/devlink.c b/net/core/devlink.c
index 1ec2e9fd8898..82703be1032e 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -4065,10 +4065,64 @@ static int devlink_nl_cmd_region_del(struct sk_buff *skb,
 	return 0;
 }
 
+static int
+devlink_nl_alloc_snapshot_id(struct devlink *devlink, struct genl_info *info,
+			     struct devlink_region *region, u32 *snapshot_id)
+{
+	struct sk_buff *msg;
+	void *hdr;
+	int err;
+
+	err = __devlink_region_snapshot_id_get(devlink, snapshot_id);
+	if (err) {
+		NL_SET_ERR_MSG_MOD(info->extack, "Failed to allocate a new snapshot id");
+		return err;
+	}
+
+	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
+	if (!msg) {
+		err = -ENOMEM;
+		goto err_msg_alloc;
+	}
+
+	hdr = genlmsg_put(msg, info->snd_portid, info->snd_seq,
+			  &devlink_nl_family, 0, DEVLINK_CMD_REGION_NEW);
+	if (!hdr) {
+		err = -EMSGSIZE;
+		goto err_put_failure;
+	}
+	err = devlink_nl_put_handle(msg, devlink);
+	if (err)
+		goto err_attr_failure;
+	err = nla_put_string(msg, DEVLINK_ATTR_REGION_NAME, region->ops->name);
+	if (err)
+		goto err_attr_failure;
+	err = nla_put_u32(msg, DEVLINK_ATTR_REGION_SNAPSHOT_ID, *snapshot_id);
+	if (err)
+		goto err_attr_failure;
+	genlmsg_end(msg, hdr);
+
+	err = genlmsg_reply(msg, info);
+	if (err)
+		goto err_reply;
+
+	return 0;
+
+err_attr_failure:
+	genlmsg_cancel(msg, hdr);
+err_put_failure:
+	nlmsg_free(msg);
+err_msg_alloc:
+err_reply:
+	__devlink_snapshot_id_decrement(devlink, *snapshot_id);
+	return err;
+}
+
 static int
 devlink_nl_cmd_region_new(struct sk_buff *skb, struct genl_info *info)
 {
 	struct devlink *devlink = info->user_ptr[0];
+	struct nlattr *snapshot_id_attr;
 	struct devlink_region *region;
 	const char *region_name;
 	u32 snapshot_id;
@@ -4080,11 +4134,6 @@ devlink_nl_cmd_region_new(struct sk_buff *skb, struct genl_info *info)
 		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) {
@@ -4102,16 +4151,24 @@ devlink_nl_cmd_region_new(struct sk_buff *skb, struct genl_info *info)
 		return -ENOSPC;
 	}
 
-	snapshot_id = nla_get_u32(info->attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID]);
+	snapshot_id_attr = info->attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID];
+	if (snapshot_id_attr) {
+		snapshot_id = nla_get_u32(snapshot_id_attr);
 
-	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;
-	}
+		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 = __devlink_snapshot_id_insert(devlink, snapshot_id);
+		if (err)
+			return err;
+	} else {
+		err = devlink_nl_alloc_snapshot_id(devlink, info,
+						   region, &snapshot_id);
+		if (err)
+			return err;
+	}
 
 	err = region->ops->snapshot(devlink, info->extack, &data);
 	if (err)
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"
 }
 
-- 
2.25.4

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